关于 PackageManagerService

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我是靠谱客的博主曾经龙猫，这篇文章主要介绍关于 PackageManagerService，现在分享给大家，希望可以做个参考。

文章目录

- - 了解 PackageManagerService
  - 了解 pm/Settings.java
  - 服务初始化过程
  - 处理 permission 文件
  - 扫描应用目录的过程
  - 当发出 Intent 时，如果系统中应用有多个相应，会弹出一个对话框让你选择？
  - 解析 APK

Android 中的应用简单可以分为两大类：系统应用和普通应用。

系统应用：系统应用是指 /system/app 或者 /system/priv-app 目录下的应用。priv-app 是4.4以后出现的，用来存放一些系统底层应用，比如 Setting、SystemUI 等。/system/app存放系统级别的应用，如 Phone、Contacts等。Android中所谓的系统应用就是这两个目录下的应用。private 应用指的是 priv-ap 目录下的。

普通应用：普通应用指的是用户安装的应用，位于 /data/app 下。普通应用还可以安装在 sd卡系统应用不可以。

通常情况下系统应用是不能删除的，但是可以升级。升级方法是安装一个包名相同但是具有更高版本好的应用在 /data/app 下，对于这种升级，Android会在 data/system/packages.xml 文件中标签记录被覆盖系统应用的升级。

了解 PackageManagerService

在应用中，如果使用 PMS 服务，是通过 Context 获取的

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    @Override
    public PackageManager getPackageManager() {
        if (mPackageManager != null) {
            return mPackageManager;
        }

        IPackageManager pm = ActivityThread.getPackageManager();
        if (pm != null) {
            // Doesn't matter if we make more than one instance.
            return (mPackageManager = new ApplicationPackageManager(this, pm));
        }

        return null;
    }

上面代码可以看出，实际上方法返回的是 ApplicationPackageManager 对象，创建对象的时候使用了 IPackageManager 作为参数。IPackageManager 对象就是 PackageManagerService 的引用对象，因此 ApplicationPackageManager 对象就是 PackageManagerService 的代理对象。ApplicationPackageManager继承自 PackageManager，PackageManager内部定义了可操作 PackageManagerService 的接口。

了解 pm/Settings.java

Setting 类的构造方法

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Settings(File dataDir, PermissionSettings permission, Object lock) {
        mLock = lock;
        mPermissions = permission;
        mRuntimePermissionsPersistence = new RuntimePermissionPersistence(mLock);
		// 创建目录 data/system 
        mSystemDir = new File(dataDir, "system");
        mSystemDir.mkdirs();
        FileUtils.setPermissions(mSystemDir.toString(),
                FileUtils.S_IRWXU|FileUtils.S_IRWXG
                |FileUtils.S_IROTH|FileUtils.S_IXOTH,
                -1, -1);
        // 创建File 记录的是 packages.xml 中所有安装应用的信息。包括 基本信息 签名 和 权限
        mSettingsFilename = new File(mSystemDir, "packages.xml");
        // packages.xml 的备份文件 当写 packages.xml 时会先备份，写成功再删除备份。
        mBackupSettingsFilename = new File(mSystemDir, "packages-backup.xml");
        // 保存普通应用的数据目录和 uid 等信息
        mPackageListFilename = new File(mSystemDir, "packages.list");
        FileUtils.setPermissions(mPackageListFilename, 0640, SYSTEM_UID, PACKAGE_INFO_GID);

final File kernelDir = new File("/config/sdcardfs");
        mKernelMappingFilename = kernelDir.exists() ? kernelDir : null;

// Deprecated: Needed for migration
        // 记录系统中被强制停止运行的应用信息。系统在强制停止运行某个应用时会把应用信息记录到这里
        mStoppedPackagesFilename = new File(mSystemDir, "packages-stopped.xml");
        // packages-stopped.xml 的备份 当写 packages-stopped.xml 时会先备份，写成功再删除备份
        mBackupStoppedPackagesFilename = new File(mSystemDir, "packages-stopped-backup.xml");
    }

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    Settings(File dataDir, PermissionSettings permission, Object lock) {
        mLock = lock;
        mPermissions = permission;
        mRuntimePermissionsPersistence = new RuntimePermissionPersistence(mLock);
		// 创建目录 data/system 
        mSystemDir = new File(dataDir, "system");
        mSystemDir.mkdirs();
        FileUtils.setPermissions(mSystemDir.toString(),
                FileUtils.S_IRWXU|FileUtils.S_IRWXG
                |FileUtils.S_IROTH|FileUtils.S_IXOTH,
                -1, -1);
        // 创建File 记录的是 packages.xml 中所有安装应用的信息。包括 基本信息 签名 和 权限
        mSettingsFilename = new File(mSystemDir, "packages.xml");
        // packages.xml 的备份文件 当写 packages.xml 时会先备份，写成功再删除备份。
        mBackupSettingsFilename = new File(mSystemDir, "packages-backup.xml");
        // 保存普通应用的数据目录和 uid 等信息
        mPackageListFilename = new File(mSystemDir, "packages.list");
        FileUtils.setPermissions(mPackageListFilename, 0640, SYSTEM_UID, PACKAGE_INFO_GID);

        final File kernelDir = new File("/config/sdcardfs");
        mKernelMappingFilename = kernelDir.exists() ? kernelDir : null;

        // Deprecated: Needed for migration
        // 记录系统中被强制停止运行的应用信息。系统在强制停止运行某个应用时会把应用信息记录到这里
        mStoppedPackagesFilename = new File(mSystemDir, "packages-stopped.xml");
        // packages-stopped.xml 的备份 当写 packages-stopped.xml 时会先备份，写成功再删除备份
        mBackupStoppedPackagesFilename = new File(mSystemDir, "packages-stopped-backup.xml");
    }

服务初始化过程

PackageManagerService 也是在 SystemServer 中初始化的，在其 run 方法中的 startBootstrapServices() 方法中有下面代码：

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        mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
                mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
        mFirstBoot = mPackageManagerService.isFirstBoot();
        mPackageManager = mSystemContext.getPackageManager();

PackageManagerService 的 main() 方法如下：

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    public static PackageManagerService main(Context context, Installer installer,
            boolean factoryTest, boolean onlyCore) {
        // Self-check for initial settings.
        PackageManagerServiceCompilerMapping.checkProperties();
		// 创建 PackageManagerService 对象
        PackageManagerService m = new PackageManagerService(context, installer,
                factoryTest, onlyCore);
        m.enableSystemUserPackages();
        // 在 ServiceManager 中注册 PackageManagerService
        ServiceManager.addService("package", m);
        // 注册 binder 服务 接收底层
        final PackageManagerNative pmn = m.new PackageManagerNative();
        ServiceManager.addService("package_native", pmn);
        return m;
    }

PackageManagerService 的构造方法

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public PackageManagerService(Context context, Installer installer,
            boolean factoryTest, boolean onlyCore) {
        LockGuard.installLock(mPackages, LockGuard.INDEX_PACKAGES);
        Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "create package manager");
        // 第一个阶段开始
        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_START,
                SystemClock.uptimeMillis());
        // 判断 sdk 版本
        if (mSdkVersion <= 0) {
            Slog.w(TAG, "**** ro.build.version.sdk not set!");
        }

mContext = context;
        // 设置运行模式 工厂模式是一种测试模式
        mFactoryTest = factoryTest;
        // onlyCore 如果为 true 只处理系统应用。一般为 false
        mOnlyCore = onlyCore;
        // 对象存储屏幕的显示信息
        mMetrics = new DisplayMetrics();
        // installer 是用来安装应用的 保存到全局变量中
        mInstaller = installer;

// Create sub-components that provide services / data. Order here is important.
        synchronized (mInstallLock) {
        synchronized (mPackages) {
            // Expose private service for system components to use.
            LocalServices.addService(
                    PackageManagerInternal.class, new PackageManagerInternalImpl());
            // 创建用户管理服务，Android支持多用户管理；通常第一个注册用户为管理员
            sUserManager = new UserManagerService(context, this,
                    new UserDataPreparer(mInstaller, mInstallLock, mContext, mOnlyCore), mPackages);
            // 初始化权限服务
            mPermissionManager = PermissionManagerService.create(context,
                    new DefaultPermissionGrantedCallback() {
                        @Override
                        public void onDefaultRuntimePermissionsGranted(int userId) {
                            synchronized(mPackages) {
                                mSettings.onDefaultRuntimePermissionsGrantedLPr(userId);
                            }
                        }
                    }, mPackages /*externalLock*/);
            mDefaultPermissionPolicy = mPermissionManager.getDefaultPermissionGrantPolicy();
            // 初始化 Settings 用来存储设置信息
            mSettings = new Settings(mPermissionManager.getPermissionSettings(), mPackages);
        }
        }

// 添加  SharedUserSetting对象到 Setting中，SharedUserId 相同的包可以运行在同一个进程中，或者相互读取资源
        // 我记得夸进程的 Android 两个app 写 sp文件 的时候，如果设置了同一个 SharedUserId 的话，是两个进程同事可以读到sp存储的内容的
        // 下面是添加了7种系统的uid
        mSettings.addSharedUserLPw("android.uid.system", Process.SYSTEM_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.phone", RADIO_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.log", LOG_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.nfc", NFC_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.bluetooth", BLUETOOTH_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.shell", SHELL_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.se", SE_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);

// 系统中读取 debug.separate_processes 属性。属性可以强制使应用程序组件运行在他自己的进程 一般调试用的
        String separateProcesses = SystemProperties.get("debug.separate_processes");
        if (separateProcesses != null && separateProcesses.length() > 0) {
            if ("*".equals(separateProcesses)) {
                mDefParseFlags = PackageParser.PARSE_IGNORE_PROCESSES;
                mSeparateProcesses = null;
                Slog.w(TAG, "Running with debug.separate_processes: * (ALL)");
            } else {
                mDefParseFlags = 0;
                mSeparateProcesses = separateProcesses.split(",");
                Slog.w(TAG, "Running with debug.separate_processes: "
                        + separateProcesses);
            }
        } else {
            mDefParseFlags = 0;
            mSeparateProcesses = null;
        }

mPackageDexOptimizer = new PackageDexOptimizer(installer, mInstallLock, context,
                "*dexopt*");
        DexManager.Listener dexManagerListener = DexLogger.getListener(this,
                installer, mInstallLock);
        // DexManager 会记录监听关于 dex 文件的加载通知等
        mDexManager = new DexManager(mContext, this, mPackageDexOptimizer, installer, mInstallLock,
                dexManagerListener);
        // ArtManagerService Art 服务，这是Binder对象，可以使得编译时使用 ART编译
        mArtManagerService = new ArtManagerService(mContext, this, installer, mInstallLock);
        mMoveCallbacks = new MoveCallbacks(FgThread.get().getLooper());

mOnPermissionChangeListeners = new OnPermissionChangeListeners(
                FgThread.get().getLooper());

getDefaultDisplayMetrics(context, mMetrics);

Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "get system config");
        // 获取系统配置
        SystemConfig systemConfig = SystemConfig.getInstance();
        mAvailableFeatures = systemConfig.getAvailableFeatures();
        Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

mProtectedPackages = new ProtectedPackages(mContext);

synchronized (mInstallLock) {
        // writer
        synchronized (mPackages) {
            // 创建用来处理消息的线程，并加入到 WatchDog 监控中。
            mHandlerThread = new ServiceThread(TAG,
                    Process.THREAD_PRIORITY_BACKGROUND, true /*allowIo*/);
            mHandlerThread.start();
            mHandler = new PackageHandler(mHandlerThread.getLooper());
            mProcessLoggingHandler = new ProcessLoggingHandler();
            // 添加线程监控
            Watchdog.getInstance().addThread(mHandler, WATCHDOG_TIMEOUT);
            mInstantAppRegistry = new InstantAppRegistry(this);
            // 得到系统中的共享库列表
            ArrayMap<String, String> libConfig = systemConfig.getSharedLibraries();
            final int builtInLibCount = libConfig.size();
            for (int i = 0; i < builtInLibCount; i++) {
                String name = libConfig.keyAt(i);
                String path = libConfig.valueAt(i);
                addSharedLibraryLPw(path, null, name, SharedLibraryInfo.VERSION_UNDEFINED,
                        SharedLibraryInfo.TYPE_BUILTIN, PLATFORM_PACKAGE_NAME, 0);
            }
            // 打开 SELinux 的 Policy 文件
            // 加载mac_permissions.xml文件，其中包含所有用于 标签的应用。
            // 加载的mac_permissions.xml文件分别是/system和/vendor分区上的plat_mac_permissions.xml和vendor_mac_permissions.xml。
            SELinuxMMAC.readInstallPolicy();

Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "loadFallbacks");
            FallbackCategoryProvider.loadFallbacks();
            Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "read user settings");
            // 解析 package.xml 中的内容 解析后插入到 mSettings 的 mPackages 变量中
            mFirstBoot = !mSettings.readLPw(sUserManager.getUsers(false));
            Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

// Clean up orphaned packages for which the code path doesn't exist
            // and they are an update to a system app - caused by bug/32321269
            final int packageSettingCount = mSettings.mPackages.size();
            for (int i = packageSettingCount - 1; i >= 0; i--) {
                PackageSetting ps = mSettings.mPackages.valueAt(i);
                if (!isExternal(ps) && (ps.codePath == null || !ps.codePath.exists())
                        && mSettings.getDisabledSystemPkgLPr(ps.name) != null) {
                    mSettings.mPackages.removeAt(i);
                    mSettings.enableSystemPackageLPw(ps.name);
                }
            }

if (mFirstBoot) {
                requestCopyPreoptedFiles();
            }
            // 设置模块代替 framework-res.apk 中缺省的 ResolverActivity 
            String customResolverActivity = Resources.getSystem().getString(
                    R.string.config_customResolverActivity);
            if (TextUtils.isEmpty(customResolverActivity)) {
                customResolverActivity = null;
            } else {
                mCustomResolverComponentName = ComponentName.unflattenFromString(
                        customResolverActivity);
            }
            // 记录开始扫描的时间
            long startTime = SystemClock.uptimeMillis();

EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_SYSTEM_SCAN_START,
                    startTime);

final String bootClassPath = System.getenv("BOOTCLASSPATH");
            final String systemServerClassPath = System.getenv("SYSTEMSERVERCLASSPATH");

if (bootClassPath == null) {
                Slog.w(TAG, "No BOOTCLASSPATH found!");
            }

if (systemServerClassPath == null) {
                Slog.w(TAG, "No SYSTEMSERVERCLASSPATH found!");
            }

File frameworkDir = new File(Environment.getRootDirectory(), "framework");

final VersionInfo ver = mSettings.getInternalVersion();
            mIsUpgrade = !Build.FINGERPRINT.equals(ver.fingerprint);
            if (mIsUpgrade) {
                logCriticalInfo(Log.INFO,
                        "Upgrading from " + ver.fingerprint + " to " + Build.FINGERPRINT);
            }

// when upgrading from pre-M, promote system app permissions from install to runtime
            // 从pre-M升级时，将系统应用程序权限从安装提升到运行时
            mPromoteSystemApps =
                    mIsUpgrade && ver.sdkVersion <= Build.VERSION_CODES.LOLLIPOP_MR1;

// When upgrading from pre-N, we need to handle package extraction like first boot,
            // as there is no profiling data available.
            mIsPreNUpgrade = mIsUpgrade && ver.sdkVersion < Build.VERSION_CODES.N;

mIsPreNMR1Upgrade = mIsUpgrade && ver.sdkVersion < Build.VERSION_CODES.N_MR1;

// save off the names of pre-existing system packages prior to scanning; we don't
            // want to automatically grant runtime permissions for new system apps
            if (mPromoteSystemApps) {
                Iterator<PackageSetting> pkgSettingIter = mSettings.mPackages.values().iterator();
                while (pkgSettingIter.hasNext()) {
                    PackageSetting ps = pkgSettingIter.next();
                    if (isSystemApp(ps)) {
                        mExistingSystemPackages.add(ps.name);
                    }
                }
            }
            // 》〉》〉》〉》〉》〉》〉下面扫描了很多文件夹》〉》〉》〉》〉》〉》〉》
            // 第二阶段 扫描系统文件 比如扫描 framework文件夹 用户的应用 或者 内置的系统应用等
            mCacheDir = preparePackageParserCache(mIsUpgrade);

// Set flag to monitor and not change apk file paths when
            // scanning install directories.
            // 设置扫描模式
            int scanFlags = SCAN_BOOTING | SCAN_INITIAL;

if (mIsUpgrade || mFirstBoot) {
                scanFlags = scanFlags | SCAN_FIRST_BOOT_OR_UPGRADE;
            }

// Collect vendor/product overlay packages. (Do this before scanning any apps.)
            // For security and version matching reason, only consider
            // overlay packages if they reside in the right directory.
            // 扫描 VENDOR_OVERLAY_DIR 这个文件夹下的信息
            scanDirTracedLI(new File(VENDOR_OVERLAY_DIR),
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR,
                    0);
            scanDirTracedLI(new File(PRODUCT_OVERLAY_DIR),
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRODUCT,
                    0);

mParallelPackageParserCallback.findStaticOverlayPackages();

// Find base frameworks (resource packages without code).
            // 扫描并收集 system/framework 信息
            scanDirTracedLI(frameworkDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_NO_DEX
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRIVILEGED,
                    0);

// Collect privileged system packages.
            // 扫描并收集 /system/prov-app 下的信息
            final File privilegedAppDir = new File(Environment.getRootDirectory(), "priv-app");
            scanDirTracedLI(privilegedAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRIVILEGED,
                    0);

// Collect ordinary system packages.
            // 扫描并收集 /system/app 下的信息
            final File systemAppDir = new File(Environment.getRootDirectory(), "app");
            scanDirTracedLI(systemAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM,
                    0);

// Collect privileged vendor packages.
            File privilegedVendorAppDir = new File(Environment.getVendorDirectory(), "priv-app");
            try {
                privilegedVendorAppDir = privilegedVendorAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(privilegedVendorAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR
                    | SCAN_AS_PRIVILEGED,
                    0);

// Collect ordinary vendor packages.
            File vendorAppDir = new File(Environment.getVendorDirectory(), "app");
            try {
                vendorAppDir = vendorAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(vendorAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR,
                    0);

// Collect privileged odm packages. /odm is another vendor partition
            // other than /vendor.
            File privilegedOdmAppDir = new File(Environment.getOdmDirectory(),
                        "priv-app");
            try {
                privilegedOdmAppDir = privilegedOdmAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(privilegedOdmAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR
                    | SCAN_AS_PRIVILEGED,
                    0);

// Collect ordinary odm packages. /odm is another vendor partition
            // other than /vendor.
            File odmAppDir = new File(Environment.getOdmDirectory(), "app");
            try {
                odmAppDir = odmAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(odmAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR,
                    0);

// Collect all OEM packages.
            final File oemAppDir = new File(Environment.getOemDirectory(), "app");
            scanDirTracedLI(oemAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_OEM,
                    0);

// Collected privileged product packages.
            File privilegedProductAppDir = new File(Environment.getProductDirectory(), "priv-app");
            try {
                privilegedProductAppDir = privilegedProductAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(privilegedProductAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRODUCT
                    | SCAN_AS_PRIVILEGED,
                    0);

// Collect ordinary product packages.
            File productAppDir = new File(Environment.getProductDirectory(), "app");
            try {
                productAppDir = productAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(productAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRODUCT,
                    0);

// Prune any system packages that no longer exist.
            // 这个列表记录可能有升级包的系统应用
            final List<String> possiblyDeletedUpdatedSystemApps = new ArrayList<>();
            // Stub packages must either be replaced with full versions in the /data
            // partition or be disabled.
            final List<String> stubSystemApps = new ArrayList<>();
            // 第三阶段 扫描 data/app 或者 data/app-priv 下的文件
            if (!mOnlyCore) {
                // 扫描并判断一些 app是否在对应的设置中存在，不存在则不能成为系统 app

// do this first before mucking with mPackages for the "expecting better" case
                final Iterator<PackageParser.Package> pkgIterator = mPackages.values().iterator();
                
                while (pkgIterator.hasNext()) {
                    final PackageParser.Package pkg = pkgIterator.next();
                    if (pkg.isStub) {
                        stubSystemApps.add(pkg.packageName);
                    }
                }

final Iterator<PackageSetting> psit = mSettings.mPackages.values().iterator();
                // 循环处理 mPackages 里面的应用
                while (psit.hasNext()) {
                    PackageSetting ps = psit.next();

/*
                     * If this is not a system app, it can't be a
                     * disable system app.
                     */
                    // 过滤掉普通应用
                    if ((ps.pkgFlags & ApplicationInfo.FLAG_SYSTEM) == 0) {
                        continue;
                    }

/*
                     * If the package is scanned, it's not erased.
                     */
                    final PackageParser.Package scannedPkg = mPackages.get(ps.name);
                    if (scannedPkg != null) {
                        /*
                         * If the system app is both scanned and in the
                         * disabled packages list, then it must have been
                         * added via OTA. Remove it from the currently
                         * scanned package so the previously user-installed
                         * application can be scanned.
                         */
                        if (mSettings.isDisabledSystemPackageLPr(ps.name)) {
                            logCriticalInfo(Log.WARN,
                                    "Expecting better updated system app for " + ps.name
                                    + "; removing system app.  Last known"
                                    + " codePath=" + ps.codePathString
                                    + ", versionCode=" + ps.versionCode
                                    + "; scanned versionCode=" + scannedPkg.getLongVersionCode());
                            // 从扫描列表 mPackages 中移除
                            removePackageLI(scannedPkg, true);
                            // 插入到 mExpectingBetter 列表 后面会进行处理
                            mExpectingBetter.put(ps.name, ps.codePath);
                        }

continue;
                    }
                    // 代表应用不再 mPackages 中，代表系统中不存在 如果这个应用也不在 <update-package> 标示中。则说明是残留应用。应该删除
                    if (!mSettings.isDisabledSystemPackageLPr(ps.name)) {
                        psit.remove();
                        logCriticalInfo(Log.WARN, "System package " + ps.name
                                + " no longer exists; it's data will be wiped");
                        // Actual deletion of code and data will be handled by later
                        // reconciliation step
                    } else {
                        // we still have a disabled system package, but, it still might have
                        // been removed. check the code path still exists and check there's
                        // still a package. the latter can happen if an OTA keeps the same
                        // code path, but, changes the package name.
                        // 这个应用不再 mPackages 中 但是在 <update-package> 标示中 加入到 possiblyDeletedUpdatedSystemApps 中
                        final PackageSetting disabledPs =
                                mSettings.getDisabledSystemPkgLPr(ps.name);
                        if (disabledPs.codePath == null || !disabledPs.codePath.exists()
                                || disabledPs.pkg == null) {
                            possiblyDeletedUpdatedSystemApps.add(ps.name);
                        }
                    }
                }
            }

//delete tmp files 删除临时文件
            deleteTempPackageFiles();

final int cachedSystemApps = PackageParser.sCachedPackageReadCount.get();

// Remove any shared userIDs that have no associated packages
            mSettings.pruneSharedUsersLPw();
            final long systemScanTime = SystemClock.uptimeMillis() - startTime;
            final int systemPackagesCount = mPackages.size();
            Slog.i(TAG, "Finished scanning system apps. Time: " + systemScanTime
                    + " ms, packageCount: " + systemPackagesCount
                    + " , timePerPackage: "
                    + (systemPackagesCount == 0 ? 0 : systemScanTime / systemPackagesCount)
                    + " , cached: " + cachedSystemApps);
            // 》〉》〉》〉》〉 到这里已经结束扫描系统app

if (mIsUpgrade && systemPackagesCount > 0) {
                MetricsLogger.histogram(null, "ota_package_manager_system_app_avg_scan_time",
                        ((int) systemScanTime) / systemPackagesCount);
            }
            // 开始处理非系统应用
            if (!mOnlyCore) {
                EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_DATA_SCAN_START,
                        SystemClock.uptimeMillis());
                // 扫描 data/app 收集目录中文件信息
                scanDirTracedLI(sAppInstallDir, 0, scanFlags | SCAN_REQUIRE_KNOWN, 0);
                // 扫描 data/priv-app 收集文件信息
                scanDirTracedLI(sDrmAppPrivateInstallDir, mDefParseFlags
                        | PackageParser.PARSE_FORWARD_LOCK,
                        scanFlags | SCAN_REQUIRE_KNOWN, 0);

// Remove disable package settings for updated system apps that were
                // removed via an OTA. If the update is no longer present, remove the
                // app completely. Otherwise, revoke their system privileges.
                // 放在possiblyDeletedUpdatedSystemApps 总的应用是 package.xml 文件被标记为带升级的系统文件
                // 但是文件却不存在。所以检查下 用户目录下是否有升级文件，看是否存在，再进行处理
                for (String deletedAppName : possiblyDeletedUpdatedSystemApps) {
                    PackageParser.Package deletedPkg = mPackages.get(deletedAppName);
                    mSettings.removeDisabledSystemPackageLPw(deletedAppName);
                    final String msg;
                    if (deletedPkg == null) {
                        // should have found an update, but, we didn't; remove everything
                        msg = "Updated system package " + deletedAppName
                                + " no longer exists; removing its data";
                        // Actual deletion of code and data will be handled by later
                        // reconciliation step
                    } else {
                        // found an update; revoke system privileges
                        msg = "Updated system package + " + deletedAppName
                                + " no longer exists; revoking system privileges";

// Don't do anything if a stub is removed from the system image. If
                        // we were to remove the uncompressed version from the /data partition,
                        // this is where it'd be done.

final PackageSetting deletedPs = mSettings.mPackages.get(deletedAppName);
                        deletedPkg.applicationInfo.flags &= ~ApplicationInfo.FLAG_SYSTEM;
                        deletedPs.pkgFlags &= ~ApplicationInfo.FLAG_SYSTEM;
                    }
                    logCriticalInfo(Log.WARN, msg);
                }

/*
                 * Make sure all system apps that we expected to appear on
                 * the userdata partition actually showed up. If they never
                 * appeared, crawl back and revive the system version.
                 */
                // mExpectingBetter 里面的应用是带系统升级的应用，前面把它从 mPackages 中移除放到了 mExpectingBetter 中
                // 最后对他们进行扫描处理
                for (int i = 0; i < mExpectingBetter.size(); i++) {
                    final String packageName = mExpectingBetter.keyAt(i);
                    if (!mPackages.containsKey(packageName)) {
                        final File scanFile = mExpectingBetter.valueAt(i);

logCriticalInfo(Log.WARN, "Expected better " + packageName
                                + " but never showed up; reverting to system");

final @ParseFlags int reparseFlags;
                        final @ScanFlags int rescanFlags;
                        // 确保应用位于下面这些文件夹内
                        if (FileUtils.contains(privilegedAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_PRIVILEGED;
                        } else if (FileUtils.contains(systemAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM;
                        } else if (FileUtils.contains(privilegedVendorAppDir, scanFile)
                                || FileUtils.contains(privilegedOdmAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_VENDOR
                                    | SCAN_AS_PRIVILEGED;
                        } else if (FileUtils.contains(vendorAppDir, scanFile)
                                || FileUtils.contains(odmAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_VENDOR;
                        } else if (FileUtils.contains(oemAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_OEM;
                        } else if (FileUtils.contains(privilegedProductAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_PRODUCT
                                    | SCAN_AS_PRIVILEGED;
                        } else if (FileUtils.contains(productAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_PRODUCT;
                        } else {
                            Slog.e(TAG, "Ignoring unexpected fallback path " + scanFile);
                            // 如果文件不在上面扫描的那些文件夹 则不做处理
                            continue;
                        }

mSettings.enableSystemPackageLPw(packageName);

try {
                            // 扫描并处理应用
                            scanPackageTracedLI(scanFile, reparseFlags, rescanFlags, 0, null);
                        } catch (PackageManagerException e) {
                            Slog.e(TAG, "Failed to parse original system package: "
                                    + e.getMessage());
                        }
                    }
                }

// Uncompress and install any stubbed system applications.
                // This must be done last to ensure all stubs are replaced or disabled.
                decompressSystemApplications(stubSystemApps, scanFlags);

final int cachedNonSystemApps = PackageParser.sCachedPackageReadCount.get()
                                - cachedSystemApps;

final long dataScanTime = SystemClock.uptimeMillis() - systemScanTime - startTime;
                final int dataPackagesCount = mPackages.size() - systemPackagesCount;
                Slog.i(TAG, "Finished scanning non-system apps. Time: " + dataScanTime
                        + " ms, packageCount: " + dataPackagesCount
                        + " , timePerPackage: "
                        + (dataPackagesCount == 0 ? 0 : dataScanTime / dataPackagesCount)
                        + " , cached: " + cachedNonSystemApps);
                if (mIsUpgrade && dataPackagesCount > 0) {
                    MetricsLogger.histogram(null, "ota_package_manager_data_app_avg_scan_time",
                            ((int) dataScanTime) / dataPackagesCount);
                }
            }
            mExpectingBetter.clear();

// Resolve the storage manager.
            mStorageManagerPackage = getStorageManagerPackageName();

// Resolve protected action filters. Only the setup wizard is allowed to
            // have a high priority filter for these actions.
            mSetupWizardPackage = getSetupWizardPackageName();
            if (mProtectedFilters.size() > 0) {
                if (DEBUG_FILTERS && mSetupWizardPackage == null) {
                    Slog.i(TAG, "No setup wizard;"
                        + " All protected intents capped to priority 0");
                }
                for (ActivityIntentInfo filter : mProtectedFilters) {
                    if (filter.activity.info.packageName.equals(mSetupWizardPackage)) {
                        if (DEBUG_FILTERS) {
                            Slog.i(TAG, "Found setup wizard;"
                                + " allow priority " + filter.getPriority() + ";"
                                + " package: " + filter.activity.info.packageName
                                + " activity: " + filter.activity.className
                                + " priority: " + filter.getPriority());
                        }
                        // skip setup wizard; allow it to keep the high priority filter
                        continue;
                    }
                    if (DEBUG_FILTERS) {
                        Slog.i(TAG, "Protected action; cap priority to 0;"
                                + " package: " + filter.activity.info.packageName
                                + " activity: " + filter.activity.className
                                + " origPrio: " + filter.getPriority());
                    }
                    filter.setPriority(0);
                }
            }

mSystemTextClassifierPackage = getSystemTextClassifierPackageName();

mDeferProtectedFilters = false;
            mProtectedFilters.clear();

// Now that we know all of the shared libraries, update all clients to have
            // the correct library paths.
            // 更新共享的动态库路径
            updateAllSharedLibrariesLPw(null);

for (SharedUserSetting setting : mSettings.getAllSharedUsersLPw()) {
                // NOTE: We ignore potential failures here during a system scan (like
                // the rest of the commands above) because there's precious little we
                // can do about it. A settings error is reported, though.
                final List<String> changedAbiCodePath =
                        adjustCpuAbisForSharedUserLPw(setting.packages, null /*scannedPackage*/);
                if (changedAbiCodePath != null && changedAbiCodePath.size() > 0) {
                    for (int i = changedAbiCodePath.size() - 1; i >= 0; --i) {
                        final String codePathString = changedAbiCodePath.get(i);
                        try {
                            mInstaller.rmdex(codePathString,
                                    getDexCodeInstructionSet(getPreferredInstructionSet()));
                        } catch (InstallerException ignored) {
                        }
                    }
                }
                // Adjust seInfo to ensure apps which share a sharedUserId are placed in the same
                // SELinux domain.
                setting.fixSeInfoLocked();
            }

// Now that we know all the packages we are keeping,
            // read and update their last usage times.
            mPackageUsage.read(mPackages);
            mCompilerStats.read();

EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_SCAN_END,
                    SystemClock.uptimeMillis());
            Slog.i(TAG, "Time to scan packages: "
                    + ((SystemClock.uptimeMillis()-startTime)/1000f)
                    + " seconds");

// If the platform SDK has changed since the last time we booted,
            // we need to re-grant app permission to catch any new ones that
            // appear.  This is really a hack, and means that apps can in some
            // cases get permissions that the user didn't initially explicitly
            // allow...  it would be nice to have some better way to handle
            // this situation.
            // 如果平台的 SDK 版本和上次启动的 SDK 版本改变了，可能权限也改变了，需要重新赋予应用权限
            final boolean sdkUpdated = (ver.sdkVersion != mSdkVersion);
            if (sdkUpdated) {
                Slog.i(TAG, "Platform changed from " + ver.sdkVersion + " to "
                        + mSdkVersion + "; regranting permissions for internal storage");
            }
            mPermissionManager.updateAllPermissions(
                    StorageManager.UUID_PRIVATE_INTERNAL, sdkUpdated, mPackages.values(),
                    mPermissionCallback);
            ver.sdkVersion = mSdkVersion;

// If this is the first boot or an update from pre-M, and it is a normal
            // boot, then we need to initialize the default preferred apps across
            // all defined users.
            // 如果这是第一次引导或pre-M的更新，这是正常的启动，然后我们需要初始化用户定义的应用程序
            if (!onlyCore && (mPromoteSystemApps || mFirstBoot)) {
                for (UserInfo user : sUserManager.getUsers(true)) {
                    mSettings.applyDefaultPreferredAppsLPw(this, user.id);
                    applyFactoryDefaultBrowserLPw(user.id);
                    primeDomainVerificationsLPw(user.id);
                }
            }

// Prepare storage for system user really early during boot,
            // since core system apps like SettingsProvider and SystemUI
            // can't wait for user to start
            final int storageFlags;
            if (StorageManager.isFileEncryptedNativeOrEmulated()) {
                storageFlags = StorageManager.FLAG_STORAGE_DE;
            } else {
                storageFlags = StorageManager.FLAG_STORAGE_DE | StorageManager.FLAG_STORAGE_CE;
            }
            List<String> deferPackages = reconcileAppsDataLI(StorageManager.UUID_PRIVATE_INTERNAL,
                    UserHandle.USER_SYSTEM, storageFlags, true /* migrateAppData */,
                    true /* onlyCoreApps */);
            mPrepareAppDataFuture = SystemServerInitThreadPool.get().submit(() -> {
                TimingsTraceLog traceLog = new TimingsTraceLog("SystemServerTimingAsync",
                        Trace.TRACE_TAG_PACKAGE_MANAGER);
                traceLog.traceBegin("AppDataFixup");
                try {
                    mInstaller.fixupAppData(StorageManager.UUID_PRIVATE_INTERNAL,
                            StorageManager.FLAG_STORAGE_DE | StorageManager.FLAG_STORAGE_CE);
                } catch (InstallerException e) {
                    Slog.w(TAG, "Trouble fixing GIDs", e);
                }
                traceLog.traceEnd();

traceLog.traceBegin("AppDataPrepare");
                if (deferPackages == null || deferPackages.isEmpty()) {
                    return;
                }
                int count = 0;
                for (String pkgName : deferPackages) {
                    PackageParser.Package pkg = null;
                    synchronized (mPackages) {
                        PackageSetting ps = mSettings.getPackageLPr(pkgName);
                        if (ps != null && ps.getInstalled(UserHandle.USER_SYSTEM)) {
                            pkg = ps.pkg;
                        }
                    }
                    if (pkg != null) {
                        synchronized (mInstallLock) {
                            prepareAppDataAndMigrateLIF(pkg, UserHandle.USER_SYSTEM, storageFlags,
                                    true /* maybeMigrateAppData */);
                        }
                        count++;
                    }
                }
                traceLog.traceEnd();
                Slog.i(TAG, "Deferred reconcileAppsData finished " + count + " packages");
            }, "prepareAppData");

// If this is first boot after an OTA, and a normal boot, then
            // we need to clear code cache directories.
            // Note that we do *not* clear the application profiles. These remain valid
            // across OTAs and are used to drive profile verification (post OTA) and
            // profile compilation (without waiting to collect a fresh set of profiles).
            if (mIsUpgrade && !onlyCore) {
                Slog.i(TAG, "Build fingerprint changed; clearing code caches");
                for (int i = 0; i < mSettings.mPackages.size(); i++) {
                    final PackageSetting ps = mSettings.mPackages.valueAt(i);
                    if (Objects.equals(StorageManager.UUID_PRIVATE_INTERNAL, ps.volumeUuid)) {
                        // No apps are running this early, so no need to freeze
                        clearAppDataLIF(ps.pkg, UserHandle.USER_ALL,
                                StorageManager.FLAG_STORAGE_DE | StorageManager.FLAG_STORAGE_CE
                                        | Installer.FLAG_CLEAR_CODE_CACHE_ONLY);
                    }
                }
                ver.fingerprint = Build.FINGERPRINT;
            }

checkDefaultBrowser();

// clear only after permissions and other defaults have been updated
            mExistingSystemPackages.clear();
            mPromoteSystemApps = false;

// All the changes are done during package scanning.
            ver.databaseVersion = Settings.CURRENT_DATABASE_VERSION;

// can downgrade to reader
            Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "write settings");
            mSettings.writeLPr();
            Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
            EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_READY,
                    SystemClock.uptimeMillis());

if (!mOnlyCore) {
                mRequiredVerifierPackage = getRequiredButNotReallyRequiredVerifierLPr();
                mRequiredInstallerPackage = getRequiredInstallerLPr();
                mRequiredUninstallerPackage = getRequiredUninstallerLPr();
                mIntentFilterVerifierComponent = getIntentFilterVerifierComponentNameLPr();
                if (mIntentFilterVerifierComponent != null) {
                    mIntentFilterVerifier = new IntentVerifierProxy(mContext,
                            mIntentFilterVerifierComponent);
                } else {
                    mIntentFilterVerifier = null;
                }
                mServicesSystemSharedLibraryPackageName = getRequiredSharedLibraryLPr(
                        PackageManager.SYSTEM_SHARED_LIBRARY_SERVICES,
                        SharedLibraryInfo.VERSION_UNDEFINED);
                mSharedSystemSharedLibraryPackageName = getRequiredSharedLibraryLPr(
                        PackageManager.SYSTEM_SHARED_LIBRARY_SHARED,
                        SharedLibraryInfo.VERSION_UNDEFINED);
            } else {
                mRequiredVerifierPackage = null;
                mRequiredInstallerPackage = null;
                mRequiredUninstallerPackage = null;
                mIntentFilterVerifierComponent = null;
                mIntentFilterVerifier = null;
                mServicesSystemSharedLibraryPackageName = null;
                mSharedSystemSharedLibraryPackageName = null;
            }
            // 创建 PackageInstallerService 管理安装会话的服务
            mInstallerService = new PackageInstallerService(context, this);
            final Pair<ComponentName, String> instantAppResolverComponent =
                    getInstantAppResolverLPr();
            if (instantAppResolverComponent != null) {
                if (DEBUG_INSTANT) {
                    Slog.d(TAG, "Set ephemeral resolver: " + instantAppResolverComponent);
                }
                mInstantAppResolverConnection = new InstantAppResolverConnection(
                        mContext, instantAppResolverComponent.first,
                        instantAppResolverComponent.second);
                mInstantAppResolverSettingsComponent =
                        getInstantAppResolverSettingsLPr(instantAppResolverComponent.first);
            } else {
                mInstantAppResolverConnection = null;
                mInstantAppResolverSettingsComponent = null;
            }
            updateInstantAppInstallerLocked(null);

// Read and update the usage of dex files.
            // Do this at the end of PM init so that all the packages have their
            // data directory reconciled.
            // At this point we know the code paths of the packages, so we can validate
            // the disk file and build the internal cache.
            // The usage file is expected to be small so loading and verifying it
            // should take a fairly small time compare to the other activities (e.g. package
            // scanning).
            final Map<Integer, List<PackageInfo>> userPackages = new HashMap<>();
            final int[] currentUserIds = UserManagerService.getInstance().getUserIds();
            for (int userId : currentUserIds) {
                userPackages.put(userId, getInstalledPackages(/*flags*/ 0, userId).getList());
            }
            mDexManager.load(userPackages);
            if (mIsUpgrade) {
                MetricsLogger.histogram(null, "ota_package_manager_init_time",
                        (int) (SystemClock.uptimeMillis() - startTime));
            }
        } // synchronized (mPackages)
        } // synchronized (mInstallLock)

// Now after opening every single application zip, make sure they
        // are all flushed.  Not really needed, but keeps things nice and
        // tidy.
        Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "GC");
        // 启动内存垃圾回收
        Runtime.getRuntime().gc();
        Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

// The initial scanning above does many calls into installd while
        // holding the mPackages lock, but we're mostly interested in yelling
        // once we have a booted system.
        mInstaller.setWarnIfHeld(mPackages);

Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
    }

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   public PackageManagerService(Context context, Installer installer,
            boolean factoryTest, boolean onlyCore) {
        LockGuard.installLock(mPackages, LockGuard.INDEX_PACKAGES);
        Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "create package manager");
        // 第一个阶段开始
        EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_START,
                SystemClock.uptimeMillis());
        // 判断 sdk 版本
        if (mSdkVersion <= 0) {
            Slog.w(TAG, "**** ro.build.version.sdk not set!");
        }

        mContext = context;
        // 设置运行模式 工厂模式是一种测试模式
        mFactoryTest = factoryTest;
        // onlyCore 如果为 true 只处理系统应用。一般为 false
        mOnlyCore = onlyCore;
        // 对象存储屏幕的显示信息
        mMetrics = new DisplayMetrics();
        // installer 是用来安装应用的 保存到全局变量中
        mInstaller = installer;

        // Create sub-components that provide services / data. Order here is important.
        synchronized (mInstallLock) {
        synchronized (mPackages) {
            // Expose private service for system components to use.
            LocalServices.addService(
                    PackageManagerInternal.class, new PackageManagerInternalImpl());
            // 创建用户管理服务，Android支持多用户管理；通常第一个注册用户为管理员
            sUserManager = new UserManagerService(context, this,
                    new UserDataPreparer(mInstaller, mInstallLock, mContext, mOnlyCore), mPackages);
            // 初始化权限服务
            mPermissionManager = PermissionManagerService.create(context,
                    new DefaultPermissionGrantedCallback() {
                        @Override
                        public void onDefaultRuntimePermissionsGranted(int userId) {
                            synchronized(mPackages) {
                                mSettings.onDefaultRuntimePermissionsGrantedLPr(userId);
                            }
                        }
                    }, mPackages /*externalLock*/);
            mDefaultPermissionPolicy = mPermissionManager.getDefaultPermissionGrantPolicy();
            // 初始化 Settings 用来存储设置信息
            mSettings = new Settings(mPermissionManager.getPermissionSettings(), mPackages);
        }
        }

        // 添加  SharedUserSetting对象到 Setting中，SharedUserId 相同的包可以运行在同一个进程中，或者相互读取资源
        // 我记得夸进程的 Android 两个app 写 sp文件 的时候，如果设置了同一个 SharedUserId 的话，是两个进程同事可以读到sp存储的内容的
        // 下面是添加了7种系统的uid
        mSettings.addSharedUserLPw("android.uid.system", Process.SYSTEM_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.phone", RADIO_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.log", LOG_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.nfc", NFC_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.bluetooth", BLUETOOTH_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.shell", SHELL_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);
        mSettings.addSharedUserLPw("android.uid.se", SE_UID,
                ApplicationInfo.FLAG_SYSTEM, ApplicationInfo.PRIVATE_FLAG_PRIVILEGED);

        // 系统中读取 debug.separate_processes 属性。属性可以强制使应用程序组件运行在他自己的进程 一般调试用的
        String separateProcesses = SystemProperties.get("debug.separate_processes");
        if (separateProcesses != null && separateProcesses.length() > 0) {
            if ("*".equals(separateProcesses)) {
                mDefParseFlags = PackageParser.PARSE_IGNORE_PROCESSES;
                mSeparateProcesses = null;
                Slog.w(TAG, "Running with debug.separate_processes: * (ALL)");
            } else {
                mDefParseFlags = 0;
                mSeparateProcesses = separateProcesses.split(",");
                Slog.w(TAG, "Running with debug.separate_processes: "
                        + separateProcesses);
            }
        } else {
            mDefParseFlags = 0;
            mSeparateProcesses = null;
        }

        mPackageDexOptimizer = new PackageDexOptimizer(installer, mInstallLock, context,
                "*dexopt*");
        DexManager.Listener dexManagerListener = DexLogger.getListener(this,
                installer, mInstallLock);
        // DexManager 会记录监听关于 dex 文件的加载通知等
        mDexManager = new DexManager(mContext, this, mPackageDexOptimizer, installer, mInstallLock,
                dexManagerListener);
        // ArtManagerService Art 服务，这是Binder对象，可以使得编译时使用 ART编译
        mArtManagerService = new ArtManagerService(mContext, this, installer, mInstallLock);
        mMoveCallbacks = new MoveCallbacks(FgThread.get().getLooper());

        mOnPermissionChangeListeners = new OnPermissionChangeListeners(
                FgThread.get().getLooper());

        getDefaultDisplayMetrics(context, mMetrics);

        Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "get system config");
        // 获取系统配置
        SystemConfig systemConfig = SystemConfig.getInstance();
        mAvailableFeatures = systemConfig.getAvailableFeatures();
        Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

        mProtectedPackages = new ProtectedPackages(mContext);

        synchronized (mInstallLock) {
        // writer
        synchronized (mPackages) {
            // 创建用来处理消息的线程，并加入到 WatchDog 监控中。
            mHandlerThread = new ServiceThread(TAG,
                    Process.THREAD_PRIORITY_BACKGROUND, true /*allowIo*/);
            mHandlerThread.start();
            mHandler = new PackageHandler(mHandlerThread.getLooper());
            mProcessLoggingHandler = new ProcessLoggingHandler();
            // 添加线程监控
            Watchdog.getInstance().addThread(mHandler, WATCHDOG_TIMEOUT);
            mInstantAppRegistry = new InstantAppRegistry(this);
            // 得到系统中的共享库列表
            ArrayMap<String, String> libConfig = systemConfig.getSharedLibraries();
            final int builtInLibCount = libConfig.size();
            for (int i = 0; i < builtInLibCount; i++) {
                String name = libConfig.keyAt(i);
                String path = libConfig.valueAt(i);
                addSharedLibraryLPw(path, null, name, SharedLibraryInfo.VERSION_UNDEFINED,
                        SharedLibraryInfo.TYPE_BUILTIN, PLATFORM_PACKAGE_NAME, 0);
            }
            // 打开 SELinux 的 Policy 文件
            // 加载mac_permissions.xml文件，其中包含所有用于 标签的应用。
            // 加载的mac_permissions.xml文件分别是/system和/vendor分区上的plat_mac_permissions.xml和vendor_mac_permissions.xml。
            SELinuxMMAC.readInstallPolicy();

            Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "loadFallbacks");
            FallbackCategoryProvider.loadFallbacks();
            Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

            Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "read user settings");
            // 解析 package.xml 中的内容 解析后插入到 mSettings 的 mPackages 变量中
            mFirstBoot = !mSettings.readLPw(sUserManager.getUsers(false));
            Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

            // Clean up orphaned packages for which the code path doesn't exist
            // and they are an update to a system app - caused by bug/32321269
            final int packageSettingCount = mSettings.mPackages.size();
            for (int i = packageSettingCount - 1; i >= 0; i--) {
                PackageSetting ps = mSettings.mPackages.valueAt(i);
                if (!isExternal(ps) && (ps.codePath == null || !ps.codePath.exists())
                        && mSettings.getDisabledSystemPkgLPr(ps.name) != null) {
                    mSettings.mPackages.removeAt(i);
                    mSettings.enableSystemPackageLPw(ps.name);
                }
            }

            if (mFirstBoot) {
                requestCopyPreoptedFiles();
            }
            // 设置模块代替 framework-res.apk 中缺省的 ResolverActivity 
            String customResolverActivity = Resources.getSystem().getString(
                    R.string.config_customResolverActivity);
            if (TextUtils.isEmpty(customResolverActivity)) {
                customResolverActivity = null;
            } else {
                mCustomResolverComponentName = ComponentName.unflattenFromString(
                        customResolverActivity);
            }
            // 记录开始扫描的时间
            long startTime = SystemClock.uptimeMillis();

            EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_SYSTEM_SCAN_START,
                    startTime);

            final String bootClassPath = System.getenv("BOOTCLASSPATH");
            final String systemServerClassPath = System.getenv("SYSTEMSERVERCLASSPATH");

            if (bootClassPath == null) {
                Slog.w(TAG, "No BOOTCLASSPATH found!");
            }

            if (systemServerClassPath == null) {
                Slog.w(TAG, "No SYSTEMSERVERCLASSPATH found!");
            }

            File frameworkDir = new File(Environment.getRootDirectory(), "framework");

            final VersionInfo ver = mSettings.getInternalVersion();
            mIsUpgrade = !Build.FINGERPRINT.equals(ver.fingerprint);
            if (mIsUpgrade) {
                logCriticalInfo(Log.INFO,
                        "Upgrading from " + ver.fingerprint + " to " + Build.FINGERPRINT);
            }

            // when upgrading from pre-M, promote system app permissions from install to runtime
            // 从pre-M升级时，将系统应用程序权限从安装提升到运行时
            mPromoteSystemApps =
                    mIsUpgrade && ver.sdkVersion <= Build.VERSION_CODES.LOLLIPOP_MR1;

            // When upgrading from pre-N, we need to handle package extraction like first boot,
            // as there is no profiling data available.
            mIsPreNUpgrade = mIsUpgrade && ver.sdkVersion < Build.VERSION_CODES.N;

            mIsPreNMR1Upgrade = mIsUpgrade && ver.sdkVersion < Build.VERSION_CODES.N_MR1;

            // save off the names of pre-existing system packages prior to scanning; we don't
            // want to automatically grant runtime permissions for new system apps
            if (mPromoteSystemApps) {
                Iterator<PackageSetting> pkgSettingIter = mSettings.mPackages.values().iterator();
                while (pkgSettingIter.hasNext()) {
                    PackageSetting ps = pkgSettingIter.next();
                    if (isSystemApp(ps)) {
                        mExistingSystemPackages.add(ps.name);
                    }
                }
            }
            // 》〉》〉》〉》〉》〉》〉下面扫描了很多文件夹》〉》〉》〉》〉》〉》〉》
            // 第二阶段 扫描系统文件 比如扫描 framework文件夹 用户的应用 或者 内置的系统应用等
            mCacheDir = preparePackageParserCache(mIsUpgrade);

            // Set flag to monitor and not change apk file paths when
            // scanning install directories.
            // 设置扫描模式
            int scanFlags = SCAN_BOOTING | SCAN_INITIAL;

            if (mIsUpgrade || mFirstBoot) {
                scanFlags = scanFlags | SCAN_FIRST_BOOT_OR_UPGRADE;
            }

            // Collect vendor/product overlay packages. (Do this before scanning any apps.)
            // For security and version matching reason, only consider
            // overlay packages if they reside in the right directory.
            // 扫描 VENDOR_OVERLAY_DIR 这个文件夹下的信息
            scanDirTracedLI(new File(VENDOR_OVERLAY_DIR),
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR,
                    0);
            scanDirTracedLI(new File(PRODUCT_OVERLAY_DIR),
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRODUCT,
                    0);

            mParallelPackageParserCallback.findStaticOverlayPackages();

            // Find base frameworks (resource packages without code).
            // 扫描并收集 system/framework 信息
            scanDirTracedLI(frameworkDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_NO_DEX
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRIVILEGED,
                    0);

            // Collect privileged system packages.
            // 扫描并收集 /system/prov-app 下的信息
            final File privilegedAppDir = new File(Environment.getRootDirectory(), "priv-app");
            scanDirTracedLI(privilegedAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRIVILEGED,
                    0);

            // Collect ordinary system packages.
            // 扫描并收集 /system/app 下的信息
            final File systemAppDir = new File(Environment.getRootDirectory(), "app");
            scanDirTracedLI(systemAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM,
                    0);

            // Collect privileged vendor packages.
            File privilegedVendorAppDir = new File(Environment.getVendorDirectory(), "priv-app");
            try {
                privilegedVendorAppDir = privilegedVendorAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(privilegedVendorAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR
                    | SCAN_AS_PRIVILEGED,
                    0);

            // Collect ordinary vendor packages.
            File vendorAppDir = new File(Environment.getVendorDirectory(), "app");
            try {
                vendorAppDir = vendorAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(vendorAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR,
                    0);

            // Collect privileged odm packages. /odm is another vendor partition
            // other than /vendor.
            File privilegedOdmAppDir = new File(Environment.getOdmDirectory(),
                        "priv-app");
            try {
                privilegedOdmAppDir = privilegedOdmAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(privilegedOdmAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR
                    | SCAN_AS_PRIVILEGED,
                    0);

            // Collect ordinary odm packages. /odm is another vendor partition
            // other than /vendor.
            File odmAppDir = new File(Environment.getOdmDirectory(), "app");
            try {
                odmAppDir = odmAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(odmAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_VENDOR,
                    0);

            // Collect all OEM packages.
            final File oemAppDir = new File(Environment.getOemDirectory(), "app");
            scanDirTracedLI(oemAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_OEM,
                    0);

            // Collected privileged product packages.
            File privilegedProductAppDir = new File(Environment.getProductDirectory(), "priv-app");
            try {
                privilegedProductAppDir = privilegedProductAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(privilegedProductAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRODUCT
                    | SCAN_AS_PRIVILEGED,
                    0);

            // Collect ordinary product packages.
            File productAppDir = new File(Environment.getProductDirectory(), "app");
            try {
                productAppDir = productAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirTracedLI(productAppDir,
                    mDefParseFlags
                    | PackageParser.PARSE_IS_SYSTEM_DIR,
                    scanFlags
                    | SCAN_AS_SYSTEM
                    | SCAN_AS_PRODUCT,
                    0);

            // Prune any system packages that no longer exist.
            // 这个列表记录可能有升级包的系统应用
            final List<String> possiblyDeletedUpdatedSystemApps = new ArrayList<>();
            // Stub packages must either be replaced with full versions in the /data
            // partition or be disabled.
            final List<String> stubSystemApps = new ArrayList<>();
            // 第三阶段 扫描 data/app 或者 data/app-priv 下的文件
            if (!mOnlyCore) {
                // 扫描并判断一些 app是否在对应的设置中存在，不存在则不能成为系统 app 

                // do this first before mucking with mPackages for the "expecting better" case
                final Iterator<PackageParser.Package> pkgIterator = mPackages.values().iterator();
                
                while (pkgIterator.hasNext()) {
                    final PackageParser.Package pkg = pkgIterator.next();
                    if (pkg.isStub) {
                        stubSystemApps.add(pkg.packageName);
                    }
                }

                final Iterator<PackageSetting> psit = mSettings.mPackages.values().iterator();
                // 循环处理 mPackages 里面的应用
                while (psit.hasNext()) {
                    PackageSetting ps = psit.next();

                    /*
                     * If this is not a system app, it can't be a
                     * disable system app.
                     */
                    // 过滤掉普通应用
                    if ((ps.pkgFlags & ApplicationInfo.FLAG_SYSTEM) == 0) {
                        continue;
                    }

                    /*
                     * If the package is scanned, it's not erased.
                     */
                    final PackageParser.Package scannedPkg = mPackages.get(ps.name);
                    if (scannedPkg != null) {
                        /*
                         * If the system app is both scanned and in the
                         * disabled packages list, then it must have been
                         * added via OTA. Remove it from the currently
                         * scanned package so the previously user-installed
                         * application can be scanned.
                         */
                        if (mSettings.isDisabledSystemPackageLPr(ps.name)) {
                            logCriticalInfo(Log.WARN,
                                    "Expecting better updated system app for " + ps.name
                                    + "; removing system app.  Last known"
                                    + " codePath=" + ps.codePathString
                                    + ", versionCode=" + ps.versionCode
                                    + "; scanned versionCode=" + scannedPkg.getLongVersionCode());
                            // 从扫描列表 mPackages 中移除
                            removePackageLI(scannedPkg, true);
                            // 插入到 mExpectingBetter 列表 后面会进行处理
                            mExpectingBetter.put(ps.name, ps.codePath);
                        }

                        continue;
                    }
                    // 代表应用不再 mPackages 中，代表系统中不存在 如果这个应用也不在 <update-package> 标示中。则说明是残留应用。应该删除
                    if (!mSettings.isDisabledSystemPackageLPr(ps.name)) {
                        psit.remove();
                        logCriticalInfo(Log.WARN, "System package " + ps.name
                                + " no longer exists; it's data will be wiped");
                        // Actual deletion of code and data will be handled by later
                        // reconciliation step
                    } else {
                        // we still have a disabled system package, but, it still might have
                        // been removed. check the code path still exists and check there's
                        // still a package. the latter can happen if an OTA keeps the same
                        // code path, but, changes the package name.
                        // 这个应用不再 mPackages 中 但是在 <update-package> 标示中 加入到 possiblyDeletedUpdatedSystemApps 中
                        final PackageSetting disabledPs =
                                mSettings.getDisabledSystemPkgLPr(ps.name);
                        if (disabledPs.codePath == null || !disabledPs.codePath.exists()
                                || disabledPs.pkg == null) {
                            possiblyDeletedUpdatedSystemApps.add(ps.name);
                        }
                    }
                }
            }

            //delete tmp files 删除临时文件
            deleteTempPackageFiles();

            final int cachedSystemApps = PackageParser.sCachedPackageReadCount.get();

            // Remove any shared userIDs that have no associated packages
            mSettings.pruneSharedUsersLPw();
            final long systemScanTime = SystemClock.uptimeMillis() - startTime;
            final int systemPackagesCount = mPackages.size();
            Slog.i(TAG, "Finished scanning system apps. Time: " + systemScanTime
                    + " ms, packageCount: " + systemPackagesCount
                    + " , timePerPackage: "
                    + (systemPackagesCount == 0 ? 0 : systemScanTime / systemPackagesCount)
                    + " , cached: " + cachedSystemApps);
            // 》〉》〉》〉》〉 到这里已经结束扫描系统app

            if (mIsUpgrade && systemPackagesCount > 0) {
                MetricsLogger.histogram(null, "ota_package_manager_system_app_avg_scan_time",
                        ((int) systemScanTime) / systemPackagesCount);
            }
            // 开始处理非系统应用
            if (!mOnlyCore) {
                EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_DATA_SCAN_START,
                        SystemClock.uptimeMillis());
                // 扫描 data/app 收集目录中文件信息
                scanDirTracedLI(sAppInstallDir, 0, scanFlags | SCAN_REQUIRE_KNOWN, 0);
                // 扫描 data/priv-app 收集文件信息
                scanDirTracedLI(sDrmAppPrivateInstallDir, mDefParseFlags
                        | PackageParser.PARSE_FORWARD_LOCK,
                        scanFlags | SCAN_REQUIRE_KNOWN, 0);

                // Remove disable package settings for updated system apps that were
                // removed via an OTA. If the update is no longer present, remove the
                // app completely. Otherwise, revoke their system privileges.
                // 放在possiblyDeletedUpdatedSystemApps 总的应用是 package.xml 文件被标记为带升级的系统文件
                // 但是文件却不存在。所以检查下 用户目录下是否有升级文件，看是否存在，再进行处理
                for (String deletedAppName : possiblyDeletedUpdatedSystemApps) {
                    PackageParser.Package deletedPkg = mPackages.get(deletedAppName);
                    mSettings.removeDisabledSystemPackageLPw(deletedAppName);
                    final String msg;
                    if (deletedPkg == null) {
                        // should have found an update, but, we didn't; remove everything
                        msg = "Updated system package " + deletedAppName
                                + " no longer exists; removing its data";
                        // Actual deletion of code and data will be handled by later
                        // reconciliation step
                    } else {
                        // found an update; revoke system privileges
                        msg = "Updated system package + " + deletedAppName
                                + " no longer exists; revoking system privileges";

                        // Don't do anything if a stub is removed from the system image. If
                        // we were to remove the uncompressed version from the /data partition,
                        // this is where it'd be done.

                        final PackageSetting deletedPs = mSettings.mPackages.get(deletedAppName);
                        deletedPkg.applicationInfo.flags &= ~ApplicationInfo.FLAG_SYSTEM;
                        deletedPs.pkgFlags &= ~ApplicationInfo.FLAG_SYSTEM;
                    }
                    logCriticalInfo(Log.WARN, msg);
                }

                /*
                 * Make sure all system apps that we expected to appear on
                 * the userdata partition actually showed up. If they never
                 * appeared, crawl back and revive the system version.
                 */
                // mExpectingBetter 里面的应用是带系统升级的应用，前面把它从 mPackages 中移除放到了 mExpectingBetter 中
                // 最后对他们进行扫描处理
                for (int i = 0; i < mExpectingBetter.size(); i++) {
                    final String packageName = mExpectingBetter.keyAt(i);
                    if (!mPackages.containsKey(packageName)) {
                        final File scanFile = mExpectingBetter.valueAt(i);

                        logCriticalInfo(Log.WARN, "Expected better " + packageName
                                + " but never showed up; reverting to system");

                        final @ParseFlags int reparseFlags;
                        final @ScanFlags int rescanFlags;
                        // 确保应用位于下面这些文件夹内
                        if (FileUtils.contains(privilegedAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_PRIVILEGED;
                        } else if (FileUtils.contains(systemAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM;
                        } else if (FileUtils.contains(privilegedVendorAppDir, scanFile)
                                || FileUtils.contains(privilegedOdmAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_VENDOR
                                    | SCAN_AS_PRIVILEGED;
                        } else if (FileUtils.contains(vendorAppDir, scanFile)
                                || FileUtils.contains(odmAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_VENDOR;
                        } else if (FileUtils.contains(oemAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_OEM;
                        } else if (FileUtils.contains(privilegedProductAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_PRODUCT
                                    | SCAN_AS_PRIVILEGED;
                        } else if (FileUtils.contains(productAppDir, scanFile)) {
                            reparseFlags =
                                    mDefParseFlags |
                                    PackageParser.PARSE_IS_SYSTEM_DIR;
                            rescanFlags =
                                    scanFlags
                                    | SCAN_AS_SYSTEM
                                    | SCAN_AS_PRODUCT;
                        } else {
                            Slog.e(TAG, "Ignoring unexpected fallback path " + scanFile);
                            // 如果文件不在上面扫描的那些文件夹 则不做处理
                            continue;
                        }

                        mSettings.enableSystemPackageLPw(packageName);

                        try {
                            // 扫描并处理应用
                            scanPackageTracedLI(scanFile, reparseFlags, rescanFlags, 0, null);
                        } catch (PackageManagerException e) {
                            Slog.e(TAG, "Failed to parse original system package: "
                                    + e.getMessage());
                        }
                    }
                }

                // Uncompress and install any stubbed system applications.
                // This must be done last to ensure all stubs are replaced or disabled.
                decompressSystemApplications(stubSystemApps, scanFlags);

                final int cachedNonSystemApps = PackageParser.sCachedPackageReadCount.get()
                                - cachedSystemApps;

                final long dataScanTime = SystemClock.uptimeMillis() - systemScanTime - startTime;
                final int dataPackagesCount = mPackages.size() - systemPackagesCount;
                Slog.i(TAG, "Finished scanning non-system apps. Time: " + dataScanTime
                        + " ms, packageCount: " + dataPackagesCount
                        + " , timePerPackage: "
                        + (dataPackagesCount == 0 ? 0 : dataScanTime / dataPackagesCount)
                        + " , cached: " + cachedNonSystemApps);
                if (mIsUpgrade && dataPackagesCount > 0) {
                    MetricsLogger.histogram(null, "ota_package_manager_data_app_avg_scan_time",
                            ((int) dataScanTime) / dataPackagesCount);
                }
            }
            mExpectingBetter.clear();

            // Resolve the storage manager.
            mStorageManagerPackage = getStorageManagerPackageName();

            // Resolve protected action filters. Only the setup wizard is allowed to
            // have a high priority filter for these actions.
            mSetupWizardPackage = getSetupWizardPackageName();
            if (mProtectedFilters.size() > 0) {
                if (DEBUG_FILTERS && mSetupWizardPackage == null) {
                    Slog.i(TAG, "No setup wizard;"
                        + " All protected intents capped to priority 0");
                }
                for (ActivityIntentInfo filter : mProtectedFilters) {
                    if (filter.activity.info.packageName.equals(mSetupWizardPackage)) {
                        if (DEBUG_FILTERS) {
                            Slog.i(TAG, "Found setup wizard;"
                                + " allow priority " + filter.getPriority() + ";"
                                + " package: " + filter.activity.info.packageName
                                + " activity: " + filter.activity.className
                                + " priority: " + filter.getPriority());
                        }
                        // skip setup wizard; allow it to keep the high priority filter
                        continue;
                    }
                    if (DEBUG_FILTERS) {
                        Slog.i(TAG, "Protected action; cap priority to 0;"
                                + " package: " + filter.activity.info.packageName
                                + " activity: " + filter.activity.className
                                + " origPrio: " + filter.getPriority());
                    }
                    filter.setPriority(0);
                }
            }

            mSystemTextClassifierPackage = getSystemTextClassifierPackageName();

            mDeferProtectedFilters = false;
            mProtectedFilters.clear();

            // Now that we know all of the shared libraries, update all clients to have
            // the correct library paths.
            // 更新共享的动态库路径
            updateAllSharedLibrariesLPw(null);

            for (SharedUserSetting setting : mSettings.getAllSharedUsersLPw()) {
                // NOTE: We ignore potential failures here during a system scan (like
                // the rest of the commands above) because there's precious little we
                // can do about it. A settings error is reported, though.
                final List<String> changedAbiCodePath =
                        adjustCpuAbisForSharedUserLPw(setting.packages, null /*scannedPackage*/);
                if (changedAbiCodePath != null && changedAbiCodePath.size() > 0) {
                    for (int i = changedAbiCodePath.size() - 1; i >= 0; --i) {
                        final String codePathString = changedAbiCodePath.get(i);
                        try {
                            mInstaller.rmdex(codePathString,
                                    getDexCodeInstructionSet(getPreferredInstructionSet()));
                        } catch (InstallerException ignored) {
                        }
                    }
                }
                // Adjust seInfo to ensure apps which share a sharedUserId are placed in the same
                // SELinux domain.
                setting.fixSeInfoLocked();
            }

            // Now that we know all the packages we are keeping,
            // read and update their last usage times.
            mPackageUsage.read(mPackages);
            mCompilerStats.read();

            EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_SCAN_END,
                    SystemClock.uptimeMillis());
            Slog.i(TAG, "Time to scan packages: "
                    + ((SystemClock.uptimeMillis()-startTime)/1000f)
                    + " seconds");

            // If the platform SDK has changed since the last time we booted,
            // we need to re-grant app permission to catch any new ones that
            // appear.  This is really a hack, and means that apps can in some
            // cases get permissions that the user didn't initially explicitly
            // allow...  it would be nice to have some better way to handle
            // this situation.
            // 如果平台的 SDK 版本和上次启动的 SDK 版本改变了，可能权限也改变了，需要重新赋予应用权限
            final boolean sdkUpdated = (ver.sdkVersion != mSdkVersion);
            if (sdkUpdated) {
                Slog.i(TAG, "Platform changed from " + ver.sdkVersion + " to "
                        + mSdkVersion + "; regranting permissions for internal storage");
            }
            mPermissionManager.updateAllPermissions(
                    StorageManager.UUID_PRIVATE_INTERNAL, sdkUpdated, mPackages.values(),
                    mPermissionCallback);
            ver.sdkVersion = mSdkVersion;

            // If this is the first boot or an update from pre-M, and it is a normal
            // boot, then we need to initialize the default preferred apps across
            // all defined users.
            // 如果这是第一次引导或pre-M的更新，这是正常的启动，然后我们需要初始化用户定义的应用程序
            if (!onlyCore && (mPromoteSystemApps || mFirstBoot)) {
                for (UserInfo user : sUserManager.getUsers(true)) {
                    mSettings.applyDefaultPreferredAppsLPw(this, user.id);
                    applyFactoryDefaultBrowserLPw(user.id);
                    primeDomainVerificationsLPw(user.id);
                }
            }

            // Prepare storage for system user really early during boot,
            // since core system apps like SettingsProvider and SystemUI
            // can't wait for user to start
            final int storageFlags;
            if (StorageManager.isFileEncryptedNativeOrEmulated()) {
                storageFlags = StorageManager.FLAG_STORAGE_DE;
            } else {
                storageFlags = StorageManager.FLAG_STORAGE_DE | StorageManager.FLAG_STORAGE_CE;
            }
            List<String> deferPackages = reconcileAppsDataLI(StorageManager.UUID_PRIVATE_INTERNAL,
                    UserHandle.USER_SYSTEM, storageFlags, true /* migrateAppData */,
                    true /* onlyCoreApps */);
            mPrepareAppDataFuture = SystemServerInitThreadPool.get().submit(() -> {
                TimingsTraceLog traceLog = new TimingsTraceLog("SystemServerTimingAsync",
                        Trace.TRACE_TAG_PACKAGE_MANAGER);
                traceLog.traceBegin("AppDataFixup");
                try {
                    mInstaller.fixupAppData(StorageManager.UUID_PRIVATE_INTERNAL,
                            StorageManager.FLAG_STORAGE_DE | StorageManager.FLAG_STORAGE_CE);
                } catch (InstallerException e) {
                    Slog.w(TAG, "Trouble fixing GIDs", e);
                }
                traceLog.traceEnd();

                traceLog.traceBegin("AppDataPrepare");
                if (deferPackages == null || deferPackages.isEmpty()) {
                    return;
                }
                int count = 0;
                for (String pkgName : deferPackages) {
                    PackageParser.Package pkg = null;
                    synchronized (mPackages) {
                        PackageSetting ps = mSettings.getPackageLPr(pkgName);
                        if (ps != null && ps.getInstalled(UserHandle.USER_SYSTEM)) {
                            pkg = ps.pkg;
                        }
                    }
                    if (pkg != null) {
                        synchronized (mInstallLock) {
                            prepareAppDataAndMigrateLIF(pkg, UserHandle.USER_SYSTEM, storageFlags,
                                    true /* maybeMigrateAppData */);
                        }
                        count++;
                    }
                }
                traceLog.traceEnd();
                Slog.i(TAG, "Deferred reconcileAppsData finished " + count + " packages");
            }, "prepareAppData");

            // If this is first boot after an OTA, and a normal boot, then
            // we need to clear code cache directories.
            // Note that we do *not* clear the application profiles. These remain valid
            // across OTAs and are used to drive profile verification (post OTA) and
            // profile compilation (without waiting to collect a fresh set of profiles).
            if (mIsUpgrade && !onlyCore) {
                Slog.i(TAG, "Build fingerprint changed; clearing code caches");
                for (int i = 0; i < mSettings.mPackages.size(); i++) {
                    final PackageSetting ps = mSettings.mPackages.valueAt(i);
                    if (Objects.equals(StorageManager.UUID_PRIVATE_INTERNAL, ps.volumeUuid)) {
                        // No apps are running this early, so no need to freeze
                        clearAppDataLIF(ps.pkg, UserHandle.USER_ALL,
                                StorageManager.FLAG_STORAGE_DE | StorageManager.FLAG_STORAGE_CE
                                        | Installer.FLAG_CLEAR_CODE_CACHE_ONLY);
                    }
                }
                ver.fingerprint = Build.FINGERPRINT;
            }

            checkDefaultBrowser();

            // clear only after permissions and other defaults have been updated
            mExistingSystemPackages.clear();
            mPromoteSystemApps = false;

            // All the changes are done during package scanning.
            ver.databaseVersion = Settings.CURRENT_DATABASE_VERSION;

            // can downgrade to reader
            Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "write settings");
            mSettings.writeLPr();
            Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
            EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_READY,
                    SystemClock.uptimeMillis());

            if (!mOnlyCore) {
                mRequiredVerifierPackage = getRequiredButNotReallyRequiredVerifierLPr();
                mRequiredInstallerPackage = getRequiredInstallerLPr();
                mRequiredUninstallerPackage = getRequiredUninstallerLPr();
                mIntentFilterVerifierComponent = getIntentFilterVerifierComponentNameLPr();
                if (mIntentFilterVerifierComponent != null) {
                    mIntentFilterVerifier = new IntentVerifierProxy(mContext,
                            mIntentFilterVerifierComponent);
                } else {
                    mIntentFilterVerifier = null;
                }
                mServicesSystemSharedLibraryPackageName = getRequiredSharedLibraryLPr(
                        PackageManager.SYSTEM_SHARED_LIBRARY_SERVICES,
                        SharedLibraryInfo.VERSION_UNDEFINED);
                mSharedSystemSharedLibraryPackageName = getRequiredSharedLibraryLPr(
                        PackageManager.SYSTEM_SHARED_LIBRARY_SHARED,
                        SharedLibraryInfo.VERSION_UNDEFINED);
            } else {
                mRequiredVerifierPackage = null;
                mRequiredInstallerPackage = null;
                mRequiredUninstallerPackage = null;
                mIntentFilterVerifierComponent = null;
                mIntentFilterVerifier = null;
                mServicesSystemSharedLibraryPackageName = null;
                mSharedSystemSharedLibraryPackageName = null;
            }
            // 创建 PackageInstallerService 管理安装会话的服务
            mInstallerService = new PackageInstallerService(context, this);
            final Pair<ComponentName, String> instantAppResolverComponent =
                    getInstantAppResolverLPr();
            if (instantAppResolverComponent != null) {
                if (DEBUG_INSTANT) {
                    Slog.d(TAG, "Set ephemeral resolver: " + instantAppResolverComponent);
                }
                mInstantAppResolverConnection = new InstantAppResolverConnection(
                        mContext, instantAppResolverComponent.first,
                        instantAppResolverComponent.second);
                mInstantAppResolverSettingsComponent =
                        getInstantAppResolverSettingsLPr(instantAppResolverComponent.first);
            } else {
                mInstantAppResolverConnection = null;
                mInstantAppResolverSettingsComponent = null;
            }
            updateInstantAppInstallerLocked(null);

            // Read and update the usage of dex files.
            // Do this at the end of PM init so that all the packages have their
            // data directory reconciled.
            // At this point we know the code paths of the packages, so we can validate
            // the disk file and build the internal cache.
            // The usage file is expected to be small so loading and verifying it
            // should take a fairly small time compare to the other activities (e.g. package
            // scanning).
            final Map<Integer, List<PackageInfo>> userPackages = new HashMap<>();
            final int[] currentUserIds = UserManagerService.getInstance().getUserIds();
            for (int userId : currentUserIds) {
                userPackages.put(userId, getInstalledPackages(/*flags*/ 0, userId).getList());
            }
            mDexManager.load(userPackages);
            if (mIsUpgrade) {
                MetricsLogger.histogram(null, "ota_package_manager_init_time",
                        (int) (SystemClock.uptimeMillis() - startTime));
            }
        } // synchronized (mPackages)
        } // synchronized (mInstallLock)

        // Now after opening every single application zip, make sure they
        // are all flushed.  Not really needed, but keeps things nice and
        // tidy.
        Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "GC");
        // 启动内存垃圾回收
        Runtime.getRuntime().gc();
        Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);

        // The initial scanning above does many calls into installd while
        // holding the mPackages lock, but we're mostly interested in yelling
        // once we have a booted system.
        mInstaller.setWarnIfHeld(mPackages);

        Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
    }

构造方法主要处理功能有：先读取 packages.xml 中上次扫描的结果，保存在 mSettings 的成员变量中，然后扫描几个目录下的应用，然后把结果保存在 PackagesServiceManager 的成员变量 mPackages 中，通过对比上次检查的结果来判断是否有升级覆盖的系统应用。如果有从 mPackages 中移除，这样 mPackages 和 mSettings 中记录一样了再写回 packages.xml 中。

处理 permission 文件

在 PackageManagerService 中的构造方法中，调用了下面代码

复制代码

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SystemConfig systemConfig = SystemConfig.getInstance();

SystemConfig 的构造方法如下，就是读取各种位置下的文件

复制代码

SystemConfig() {
        // Read configuration from system
        readPermissions(Environment.buildPath(
                Environment.getRootDirectory(), "etc", "sysconfig"), ALLOW_ALL);

// Read configuration from the old permissions dir
        readPermissions(Environment.buildPath(
                Environment.getRootDirectory(), "etc", "permissions"), ALLOW_ALL);

// Vendors are only allowed to customze libs, features and privapp permissions
        int vendorPermissionFlag = ALLOW_LIBS | ALLOW_FEATURES | ALLOW_PRIVAPP_PERMISSIONS;
        if (Build.VERSION.FIRST_SDK_INT <= Build.VERSION_CODES.O_MR1) {
            // For backward compatibility
            vendorPermissionFlag |= (ALLOW_PERMISSIONS | ALLOW_APP_CONFIGS);
        }
        readPermissions(Environment.buildPath(
                Environment.getVendorDirectory(), "etc", "sysconfig"), vendorPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getVendorDirectory(), "etc", "permissions"), vendorPermissionFlag);

// Allow ODM to customize system configs as much as Vendor, because /odm is another
        // vendor partition other than /vendor.
        int odmPermissionFlag = vendorPermissionFlag;
        readPermissions(Environment.buildPath(
                Environment.getOdmDirectory(), "etc", "sysconfig"), odmPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getOdmDirectory(), "etc", "permissions"), odmPermissionFlag);

// Allow OEM to customize features and OEM permissions
        int oemPermissionFlag = ALLOW_FEATURES | ALLOW_OEM_PERMISSIONS;
        readPermissions(Environment.buildPath(
                Environment.getOemDirectory(), "etc", "sysconfig"), oemPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getOemDirectory(), "etc", "permissions"), oemPermissionFlag);

// Allow Product to customize system configs around libs, features, permissions and apps
        int productPermissionFlag = ALLOW_LIBS | ALLOW_FEATURES | ALLOW_PERMISSIONS |
                ALLOW_APP_CONFIGS | ALLOW_PRIVAPP_PERMISSIONS;
        readPermissions(Environment.buildPath(
                Environment.getProductDirectory(), "etc", "sysconfig"), productPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getProductDirectory(), "etc", "permissions"), productPermissionFlag);
    }

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   SystemConfig() {
        // Read configuration from system
        readPermissions(Environment.buildPath(
                Environment.getRootDirectory(), "etc", "sysconfig"), ALLOW_ALL);

        // Read configuration from the old permissions dir
        readPermissions(Environment.buildPath(
                Environment.getRootDirectory(), "etc", "permissions"), ALLOW_ALL);

        // Vendors are only allowed to customze libs, features and privapp permissions
        int vendorPermissionFlag = ALLOW_LIBS | ALLOW_FEATURES | ALLOW_PRIVAPP_PERMISSIONS;
        if (Build.VERSION.FIRST_SDK_INT <= Build.VERSION_CODES.O_MR1) {
            // For backward compatibility
            vendorPermissionFlag |= (ALLOW_PERMISSIONS | ALLOW_APP_CONFIGS);
        }
        readPermissions(Environment.buildPath(
                Environment.getVendorDirectory(), "etc", "sysconfig"), vendorPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getVendorDirectory(), "etc", "permissions"), vendorPermissionFlag);

        // Allow ODM to customize system configs as much as Vendor, because /odm is another
        // vendor partition other than /vendor.
        int odmPermissionFlag = vendorPermissionFlag;
        readPermissions(Environment.buildPath(
                Environment.getOdmDirectory(), "etc", "sysconfig"), odmPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getOdmDirectory(), "etc", "permissions"), odmPermissionFlag);

        // Allow OEM to customize features and OEM permissions
        int oemPermissionFlag = ALLOW_FEATURES | ALLOW_OEM_PERMISSIONS;
        readPermissions(Environment.buildPath(
                Environment.getOemDirectory(), "etc", "sysconfig"), oemPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getOemDirectory(), "etc", "permissions"), oemPermissionFlag);

        // Allow Product to customize system configs around libs, features, permissions and apps
        int productPermissionFlag = ALLOW_LIBS | ALLOW_FEATURES | ALLOW_PERMISSIONS |
                ALLOW_APP_CONFIGS | ALLOW_PRIVAPP_PERMISSIONS;
        readPermissions(Environment.buildPath(
                Environment.getProductDirectory(), "etc", "sysconfig"), productPermissionFlag);
        readPermissions(Environment.buildPath(
                Environment.getProductDirectory(), "etc", "permissions"), productPermissionFlag);
    }

Permission 是通过 readPermissions() 方法完成的

复制代码

void readPermissions(File libraryDir, int permissionFlag) {
        // Read permissions from given directory.
        // 如果文件夹不存在 或者 不是文件夹 返回
        if (!libraryDir.exists() || !libraryDir.isDirectory()) {
            if (permissionFlag == ALLOW_ALL) {
                Slog.w(TAG, "No directory " + libraryDir + ", skipping");
            }
            return;
        }
        // 如果文件夹不可读 返回
        if (!libraryDir.canRead()) {
            Slog.w(TAG, "Directory " + libraryDir + " cannot be read");
            return;
        }

// Iterate over the files in the directory and scan .xml files
        File platformFile = null;
        for (File f : libraryDir.listFiles()) {
            // We'll read platform.xml last
            // 先不处理 platform.xml 文件 最后处理
            if (f.getPath().endsWith("etc/permissions/platform.xml")) {
                platformFile = f;
                continue;
            }
            // 不是 xml 文件不处理
            if (!f.getPath().endsWith(".xml")) {
                Slog.i(TAG, "Non-xml file " + f + " in " + libraryDir + " directory, ignoring");
                continue;
            }
            // 文件不可读不处理
            if (!f.canRead()) {
                Slog.w(TAG, "Permissions library file " + f + " cannot be read");
                continue;
            }
            // 解析 xml 文件
            readPermissionsFromXml(f, permissionFlag);
        }

// Read platform permissions last so it will take precedence
        // 单独处理 platformFile 文件
        if (platformFile != null) {
            readPermissionsFromXml(platformFile, permissionFlag);
        }
    }

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     void readPermissions(File libraryDir, int permissionFlag) {
        // Read permissions from given directory.
        // 如果文件夹不存在 或者 不是文件夹 返回
        if (!libraryDir.exists() || !libraryDir.isDirectory()) {
            if (permissionFlag == ALLOW_ALL) {
                Slog.w(TAG, "No directory " + libraryDir + ", skipping");
            }
            return;
        }
        // 如果文件夹不可读 返回
        if (!libraryDir.canRead()) {
            Slog.w(TAG, "Directory " + libraryDir + " cannot be read");
            return;
        }

        // Iterate over the files in the directory and scan .xml files
        File platformFile = null;
        for (File f : libraryDir.listFiles()) {
            // We'll read platform.xml last
            // 先不处理 platform.xml 文件 最后处理
            if (f.getPath().endsWith("etc/permissions/platform.xml")) {
                platformFile = f;
                continue;
            }
            // 不是 xml 文件不处理
            if (!f.getPath().endsWith(".xml")) {
                Slog.i(TAG, "Non-xml file " + f + " in " + libraryDir + " directory, ignoring");
                continue;
            }
            // 文件不可读不处理
            if (!f.canRead()) {
                Slog.w(TAG, "Permissions library file " + f + " cannot be read");
                continue;
            }
            // 解析 xml 文件
            readPermissionsFromXml(f, permissionFlag);
        }

        // Read platform permissions last so it will take precedence
        // 单独处理 platformFile 文件
        if (platformFile != null) {
            readPermissionsFromXml(platformFile, permissionFlag);
        }
    }

readPermissions 就是通过读取指定目录下的 xml 文件，然后通过调用 readPermissionsFromXml 解析文件。目录下存放的是 permission 相关的文件。其中 platform.xml 的文件内容和其他文件不同，比如 android.hardware.audio.low.latency.xml 文件如下

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<?xml version="1.0" encoding="utf-8"?>
<permissions>
    <feature name="android.hardware.audio.low_latency" />
</permissions>

文件只是定义了一个 feature 标签。除了 platform.xml 其他文件也一样，下面是 platform.xml 文件

复制代码

<permission name="android.permission.MANAGE_VOICE_KEYPHRASES">
        <group gid="audio" ></group>
    </permission>

<assign-permission name="android.permission.ACCESS_LOWPAN_STATE" uid="lowpan" ></assign-permission>
    <assign-permission name="android.permission.MANAGE_LOWPAN_INTERFACES" uid="lowpan" ></assign-permission>
	// ...
	// ...
    <library name="android.test.base"
            file="/system/framework/android.test.base.jar" ></library>
    <library name="android.test.mock"
            file="/system/framework/android.test.mock.jar" ></library>
    <library name="android.test.runner"
            file="/system/framework/android.test.runner.jar" ></library>
    <library name="javax.obex"
            file="/system/framework/javax.obex.jar" ></library>
    <library name="org.apache.http.legacy"
            file="/system/framework/org.apache.http.legacy.boot.jar" ></library>
    
    <allow-in-power-save-except-idle package="com.android.providers.calendar" ></allow-in-power-save-except-idle>
    <allow-in-power-save-except-idle package="com.android.providers.contacts" ></allow-in-power-save-except-idle>

<system-user-whitelisted-app package="com.android.settings" ></system-user-whitelisted-app>

<system-user-blacklisted-app package="com.android.wallpaper.livepicker" ></system-user-blacklisted-app>
</permissions>

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<permissions>
    <permission name="android.permission.BLUETOOTH_ADMIN" >
        <group gid="net_bt_admin" />
    </permission>

    <permission name="android.permission.LOOP_RADIO" >
        <group gid="loop_radio" />
    </permission>

    <!-- Hotword training apps sometimes need a GID to talk with low-level
         hardware; give them audio for now until full HAL support is added. -->
    <permission name="android.permission.MANAGE_VOICE_KEYPHRASES">
        <group gid="audio" />
    </permission>

    <permission name="android.permission.ACCESS_BROADCAST_RADIO" >
        <!-- /dev/fm is gid media, not audio -->
        <group gid="media" />
    </permission>

    <permission name="android.permission.USE_RESERVED_DISK">
        <group gid="reserved_disk" />
    </permission>

    <permission name="android.permission.READ_EXTERNAL_STORAGE" />
    <permission name="android.permission.WRITE_EXTERNAL_STORAGE" />
	// ...
	// ...
    <assign-permission name="android.permission.DUMP" uid="incidentd" />
    <assign-permission name="android.permission.PACKAGE_USAGE_STATS" uid="incidentd" />
    <assign-permission name="android.permission.INTERACT_ACROSS_USERS" uid="incidentd" />

    <assign-permission name="android.permission.ACCESS_LOWPAN_STATE" uid="lowpan" />
    <assign-permission name="android.permission.MANAGE_LOWPAN_INTERFACES" uid="lowpan" />
	// ...
	// ...
    <library name="android.test.base"
            file="/system/framework/android.test.base.jar" />
    <library name="android.test.mock"
            file="/system/framework/android.test.mock.jar" />
    <library name="android.test.runner"
            file="/system/framework/android.test.runner.jar" />
    <library name="javax.obex"
            file="/system/framework/javax.obex.jar" />
    <library name="org.apache.http.legacy"
            file="/system/framework/org.apache.http.legacy.boot.jar" />
    <!-- Whitelist system providers -->
    <allow-in-power-save-except-idle package="com.android.providers.calendar" />
    <allow-in-power-save-except-idle package="com.android.providers.contacts" />

    <!-- These are the packages that are white-listed to be able to run as system user -->
    <system-user-whitelisted-app package="com.android.settings" />

    <!-- These are the packages that shouldn't run as system user -->
    <system-user-blacklisted-app package="com.android.wallpaper.livepicker" />
</permissions>

标签 permission ：表示把属性 name 中的字符串表示的权限赋予 group 标签中的属性 gid 中的用户组。
标签 assign-permission ：表示把属性 name 中的权限赋予 uid 中的用户。
标签 library ：表示除了 framework 动态库以外，系统将为应用加载动态库。

readPermissionsFromXml() 方法主要工作就是解析上面那些标签。内部就是解析 xml 而已，解析的结果

标签 permission 中的结果：把属性 name 中的字符串表示的权限和 group 中的 gid 都存到 mSettings中的 mPermissions 中，而所有gid 也被收集起来放到了 PackageManagerService 的 mGlobalGids 中。
标签assign-permission 中的内容放到了 PackageManagerService 的成员变量 mSystemPermission 中
library 动态库放到了 PackageServiceManager 中的 mSharedLibraries 中。
其他 xml 文件中的 feature 定义的字符串放到了 PackageManagerService 的成员变量 mAvailableFeature 中。

Android的很多功能需要 permission 来保护，应用中如果需要某个受保护的功能，需要在他的 AndroidManifest 中显示的声明该字符串。但是有些功能只能特定的用户组使用，platform.xml 就是定义这种限制规则。

扫描应用目录的过程

在 PackageManagerService 的构造方法中，调用了很多次 scanDirTracedLI() 去扫描文件，scanDirTracedLI内部实际上调用了代码 scanDirLI() 扫描文件，代码如下
// scanDirLI 本身并不扫描子目录，且只扫描apk文件。其内部调用了scanPackageChildLI 继续扫描过程

复制代码

private void scanDirLI(File scanDir, int parseFlags, int scanFlags, long currentTime) {
        // 获取所有文件 File
        final File[] files = scanDir.listFiles();
        // 如果是空的直接返回
        if (ArrayUtils.isEmpty(files)) {
            Log.d(TAG, "No files in app dir " + scanDir);
            return;
        }

if (DEBUG_PACKAGE_SCANNING) {
            Log.d(TAG, "Scanning app dir " + scanDir + " scanFlags=" + scanFlags
                    + " flags=0x" + Integer.toHexString(parseFlags));
        }
        try (ParallelPackageParser parallelPackageParser = new ParallelPackageParser(
                mSeparateProcesses, mOnlyCore, mMetrics, mCacheDir,
                mParallelPackageParserCallback)) {
            // Submit files for parsing in parallel
            int fileCount = 0;
            for (File file : files) {
                // 判断是否是应用文件 不处理不是应用的文件
                final boolean isPackage = (isApkFile(file) || file.isDirectory())
                        && !PackageInstallerService.isStageName(file.getName());
                if (!isPackage) {
                    // Ignore entries which are not packages
                    continue;
                }
                // 内部解析创建了 PackageParser 并加入到  BlockingQueue<ParseResult> mQueue 阻塞队列中，等待执行
                parallelPackageParser.submit(file, parseFlags);
                // 记录文件数量
                fileCount++;
            }

// Process results one by one
            for (; fileCount > 0; fileCount--) {
                // 循环 每次拿出上面加入到队列中的头文件
                ParallelPackageParser.ParseResult parseResult = parallelPackageParser.take();
                Throwable throwable = parseResult.throwable;
                int errorCode = PackageManager.INSTALL_SUCCEEDED;

if (throwable == null) {
                    // TODO(toddke): move lower in the scan chain
                    // Static shared libraries have synthetic package names
                    if (parseResult.pkg.applicationInfo.isStaticSharedLibrary()) {
                        renameStaticSharedLibraryPackage(parseResult.pkg);
                    }
                    try {
                        if (errorCode == PackageManager.INSTALL_SUCCEEDED) {
                            // 继续扫描过程 包含了校验签名等操作
                            scanPackageChildLI(parseResult.pkg, parseFlags, scanFlags,
                                    currentTime, null);
                        }
                    } catch (PackageManagerException e) {
                        errorCode = e.error;
                        Slog.w(TAG, "Failed to scan " + parseResult.scanFile + ": " + e.getMessage());
                    }
                } else if (throwable instanceof PackageParser.PackageParserException) {
                    PackageParser.PackageParserException e = (PackageParser.PackageParserException)
                            throwable;
                    errorCode = e.error;
                    Slog.w(TAG, "Failed to parse " + parseResult.scanFile + ": " + e.getMessage());
                } else {
                    throw new IllegalStateException("Unexpected exception occurred while parsing "
                            + parseResult.scanFile, throwable);
                }

// Delete invalid userdata apps
                if ((scanFlags & SCAN_AS_SYSTEM) == 0 &&
                        errorCode != PackageManager.INSTALL_SUCCEEDED) {
                    // 删除安装未成功的文件和数据目录
                    logCriticalInfo(Log.WARN,
                            "Deleting invalid package at " + parseResult.scanFile);
                    removeCodePathLI(parseResult.scanFile);
                }
            }
        }
    }

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    private void scanDirLI(File scanDir, int parseFlags, int scanFlags, long currentTime) {
        // 获取所有文件 File
        final File[] files = scanDir.listFiles();
        // 如果是空的直接返回
        if (ArrayUtils.isEmpty(files)) {
            Log.d(TAG, "No files in app dir " + scanDir);
            return;
        }

        if (DEBUG_PACKAGE_SCANNING) {
            Log.d(TAG, "Scanning app dir " + scanDir + " scanFlags=" + scanFlags
                    + " flags=0x" + Integer.toHexString(parseFlags));
        }
        try (ParallelPackageParser parallelPackageParser = new ParallelPackageParser(
                mSeparateProcesses, mOnlyCore, mMetrics, mCacheDir,
                mParallelPackageParserCallback)) {
            // Submit files for parsing in parallel
            int fileCount = 0;
            for (File file : files) {
                // 判断是否是应用文件 不处理不是应用的文件
                final boolean isPackage = (isApkFile(file) || file.isDirectory())
                        && !PackageInstallerService.isStageName(file.getName());
                if (!isPackage) {
                    // Ignore entries which are not packages
                    continue;
                }
                // 内部解析创建了 PackageParser 并加入到  BlockingQueue<ParseResult> mQueue 阻塞队列中，等待执行
                parallelPackageParser.submit(file, parseFlags);
                // 记录文件数量
                fileCount++;
            }

            // Process results one by one
            for (; fileCount > 0; fileCount--) {
                // 循环 每次拿出上面加入到队列中的头文件
                ParallelPackageParser.ParseResult parseResult = parallelPackageParser.take();
                Throwable throwable = parseResult.throwable;
                int errorCode = PackageManager.INSTALL_SUCCEEDED;

                if (throwable == null) {
                    // TODO(toddke): move lower in the scan chain
                    // Static shared libraries have synthetic package names
                    if (parseResult.pkg.applicationInfo.isStaticSharedLibrary()) {
                        renameStaticSharedLibraryPackage(parseResult.pkg);
                    }
                    try {
                        if (errorCode == PackageManager.INSTALL_SUCCEEDED) {
                            // 继续扫描过程 包含了校验签名等操作
                            scanPackageChildLI(parseResult.pkg, parseFlags, scanFlags,
                                    currentTime, null);
                        }
                    } catch (PackageManagerException e) {
                        errorCode = e.error;
                        Slog.w(TAG, "Failed to scan " + parseResult.scanFile + ": " + e.getMessage());
                    }
                } else if (throwable instanceof PackageParser.PackageParserException) {
                    PackageParser.PackageParserException e = (PackageParser.PackageParserException)
                            throwable;
                    errorCode = e.error;
                    Slog.w(TAG, "Failed to parse " + parseResult.scanFile + ": " + e.getMessage());
                } else {
                    throw new IllegalStateException("Unexpected exception occurred while parsing "
                            + parseResult.scanFile, throwable);
                }

                // Delete invalid userdata apps
                if ((scanFlags & SCAN_AS_SYSTEM) == 0 &&
                        errorCode != PackageManager.INSTALL_SUCCEEDED) {
                    // 删除安装未成功的文件和数据目录
                    logCriticalInfo(Log.WARN,
                            "Deleting invalid package at " + parseResult.scanFile);
                    removeCodePathLI(parseResult.scanFile);
                }
            }
        }
    }

继续扫描过程 scanPackageChildLI

复制代码

private PackageParser.Package scanPackageChildLI(PackageParser.Package pkg,
            final @ParseFlags int parseFlags, @ScanFlags int scanFlags, long currentTime,
            @Nullable UserHandle user)
                    throws PackageManagerException {
        // If the package has children and this is the first dive in the function
        // we scan the package with the SCAN_CHECK_ONLY flag set to see whether all
        // packages (parent and children) would be successfully scanned before the
        // actual scan since scanning mutates internal state and we want to atomically
        // install the package and its children.
        // 判断是否有子目录 设置对应的 flag
        if ((scanFlags & SCAN_CHECK_ONLY) == 0) {
            if (pkg.childPackages != null && pkg.childPackages.size() > 0) {
                scanFlags |= SCAN_CHECK_ONLY;
            }
        } else {
            scanFlags &= ~SCAN_CHECK_ONLY;
        }

// Scan the parent
        // 对位于Rom的软件包进行检查，包括系统，供应商，签名，版本等信息检查，如果新包的版本低或者签名缺失等则会删除data/ 下的包（内部调用了 collectCertificatesLI 校验签名）
        PackageParser.Package scannedPkg = addForInitLI(pkg, parseFlags,
                scanFlags, currentTime, user);

// Scan the children
        final int childCount = (pkg.childPackages != null) ? pkg.childPackages.size() : 0;
        for (int i = 0; i < childCount; i++) {
            PackageParser.Package childPackage = pkg.childPackages.get(i);
            addForInitLI(childPackage, parseFlags, scanFlags,
                    currentTime, user);
        }

if ((scanFlags & SCAN_CHECK_ONLY) != 0) {
            return scanPackageChildLI(pkg, parseFlags, scanFlags, currentTime, user);
        }

return scannedPkg;
    }

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    private PackageParser.Package scanPackageChildLI(PackageParser.Package pkg,
            final @ParseFlags int parseFlags, @ScanFlags int scanFlags, long currentTime,
            @Nullable UserHandle user)
                    throws PackageManagerException {
        // If the package has children and this is the first dive in the function
        // we scan the package with the SCAN_CHECK_ONLY flag set to see whether all
        // packages (parent and children) would be successfully scanned before the
        // actual scan since scanning mutates internal state and we want to atomically
        // install the package and its children.
        // 判断是否有子目录 设置对应的 flag
        if ((scanFlags & SCAN_CHECK_ONLY) == 0) {
            if (pkg.childPackages != null && pkg.childPackages.size() > 0) {
                scanFlags |= SCAN_CHECK_ONLY;
            }
        } else {
            scanFlags &= ~SCAN_CHECK_ONLY;
        }

        // Scan the parent
        // 对位于Rom的软件包进行检查，包括系统，供应商，签名，版本等信息检查，如果新包的版本低或者签名缺失等则会删除data/ 下的包（内部调用了 collectCertificatesLI 校验签名）
        PackageParser.Package scannedPkg = addForInitLI(pkg, parseFlags,
                scanFlags, currentTime, user);

        // Scan the children
        final int childCount = (pkg.childPackages != null) ? pkg.childPackages.size() : 0;
        for (int i = 0; i < childCount; i++) {
            PackageParser.Package childPackage = pkg.childPackages.get(i);
            addForInitLI(childPackage, parseFlags, scanFlags,
                    currentTime, user);
        }


        if ((scanFlags & SCAN_CHECK_ONLY) != 0) {
            return scanPackageChildLI(pkg, parseFlags, scanFlags, currentTime, user);
        }

        return scannedPkg;
    }

当发出 Intent 时，如果系统中应用有多个相应，会弹出一个对话框让你选择？

在上面的代码中调用了 addForInitLI() ，在addForInitLI中调用了 scanPackageNewLI() -> commitScanResultsLocked() -> commitPackageSettings() ;
在 commitPackageSettings 中初始化了一个 ResolverActivity ；这个Activity 就是弹出对话框的页面。

复制代码

// mResolveActivity 为成员变量 
if (pkg.packageName.equals("android")) {
            synchronized (mPackages) {
                if ((scanFlags & SCAN_CHECK_ONLY) == 0) {
                    // Set up information for our fall-back user intent resolution activity.
                    mPlatformPackage = pkg;
                    pkg.mVersionCode = mSdkVersion;
                    pkg.mVersionCodeMajor = 0;
                    mAndroidApplication = pkg.applicationInfo;
                    if (!mResolverReplaced) {
                        mResolveActivity.applicationInfo = mAndroidApplication;
                        mResolveActivity.name = ResolverActivity.class.getName();
                        mResolveActivity.packageName = mAndroidApplication.packageName;
                        mResolveActivity.processName = "system:ui";
                        mResolveActivity.launchMode = ActivityInfo.LAUNCH_MULTIPLE;
                        mResolveActivity.documentLaunchMode = ActivityInfo.DOCUMENT_LAUNCH_NEVER;
                        mResolveActivity.flags = ActivityInfo.FLAG_EXCLUDE_FROM_RECENTS;
                        mResolveActivity.theme = R.style.Theme_Material_Dialog_Alert;
                        mResolveActivity.exported = true;
                        mResolveActivity.enabled = true;
                        mResolveActivity.resizeMode = ActivityInfo.RESIZE_MODE_RESIZEABLE;
                        mResolveActivity.configChanges = ActivityInfo.CONFIG_SCREEN_SIZE
                                | ActivityInfo.CONFIG_SMALLEST_SCREEN_SIZE
                                | ActivityInfo.CONFIG_SCREEN_LAYOUT
                                | ActivityInfo.CONFIG_ORIENTATION
                                | ActivityInfo.CONFIG_KEYBOARD
                                | ActivityInfo.CONFIG_KEYBOARD_HIDDEN;
                        mResolveInfo.activityInfo = mResolveActivity;
                        mResolveInfo.priority = 0;
                        mResolveInfo.preferredOrder = 0;
                        mResolveInfo.match = 0;
                        mResolveComponentName = new ComponentName(
                                mAndroidApplication.packageName, mResolveActivity.name);
                    }
                }
            }
        }

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// mResolveActivity 为成员变量 
if (pkg.packageName.equals("android")) {
            synchronized (mPackages) {
                if ((scanFlags & SCAN_CHECK_ONLY) == 0) {
                    // Set up information for our fall-back user intent resolution activity.
                    mPlatformPackage = pkg;
                    pkg.mVersionCode = mSdkVersion;
                    pkg.mVersionCodeMajor = 0;
                    mAndroidApplication = pkg.applicationInfo;
                    if (!mResolverReplaced) {
                        mResolveActivity.applicationInfo = mAndroidApplication;
                        mResolveActivity.name = ResolverActivity.class.getName();
                        mResolveActivity.packageName = mAndroidApplication.packageName;
                        mResolveActivity.processName = "system:ui";
                        mResolveActivity.launchMode = ActivityInfo.LAUNCH_MULTIPLE;
                        mResolveActivity.documentLaunchMode = ActivityInfo.DOCUMENT_LAUNCH_NEVER;
                        mResolveActivity.flags = ActivityInfo.FLAG_EXCLUDE_FROM_RECENTS;
                        mResolveActivity.theme = R.style.Theme_Material_Dialog_Alert;
                        mResolveActivity.exported = true;
                        mResolveActivity.enabled = true;
                        mResolveActivity.resizeMode = ActivityInfo.RESIZE_MODE_RESIZEABLE;
                        mResolveActivity.configChanges = ActivityInfo.CONFIG_SCREEN_SIZE
                                | ActivityInfo.CONFIG_SMALLEST_SCREEN_SIZE
                                | ActivityInfo.CONFIG_SCREEN_LAYOUT
                                | ActivityInfo.CONFIG_ORIENTATION
                                | ActivityInfo.CONFIG_KEYBOARD
                                | ActivityInfo.CONFIG_KEYBOARD_HIDDEN;
                        mResolveInfo.activityInfo = mResolveActivity;
                        mResolveInfo.priority = 0;
                        mResolveInfo.preferredOrder = 0;
                        mResolveInfo.match = 0;
                        mResolveComponentName = new ComponentName(
                                mAndroidApplication.packageName, mResolveActivity.name);
                    }
                }
            }
        }

解析 APK

在构造器中调用的 scanDirLI() 方法中，通过 ParallelPackageParser 来解析 APK，ParallelPackageParser 内部则是创建了 PackageParser 对象来解析。下面是 PackageParser 解析方法。

复制代码

public Package parsePackage(File packageFile, int flags, boolean useCaches)
            throws PackageParserException {
        // 从 Cached 中获取如果解析过直接返回
        Package parsed = useCaches ? getCachedResult(packageFile, flags) : null;
        if (parsed != null) {
            return parsed;
        }

long parseTime = LOG_PARSE_TIMINGS ? SystemClock.uptimeMillis() : 0;
        if (packageFile.isDirectory()) {
            // 如果是文件夹调用parseClusterPackage 主要为了关联多个apk存储到一个文件夹下的情况
            // 下面有介绍
            parsed = parseClusterPackage(packageFile, flags);
        } else {
            // 如果是文件调用 parseMonolithicPackage
            // 下面有介绍
            parsed = parseMonolithicPackage(packageFile, flags);
        }

long cacheTime = LOG_PARSE_TIMINGS ? SystemClock.uptimeMillis() : 0;
        // 缓存结果
        cacheResult(packageFile, flags, parsed);
        // 打 Log
        if (LOG_PARSE_TIMINGS) {
            parseTime = cacheTime - parseTime;
            cacheTime = SystemClock.uptimeMillis() - cacheTime;
            if (parseTime + cacheTime > LOG_PARSE_TIMINGS_THRESHOLD_MS) {
                Slog.i(TAG, "Parse times for '" + packageFile + "': parse=" + parseTime
                        + "ms, update_cache=" + cacheTime + " ms");
            }
        }
        return parsed;
    }

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    public Package parsePackage(File packageFile, int flags, boolean useCaches)
            throws PackageParserException {
        // 从 Cached 中获取如果解析过直接返回
        Package parsed = useCaches ? getCachedResult(packageFile, flags) : null;
        if (parsed != null) {
            return parsed;
        }

        long parseTime = LOG_PARSE_TIMINGS ? SystemClock.uptimeMillis() : 0;
        if (packageFile.isDirectory()) {
            // 如果是文件夹调用parseClusterPackage 主要为了关联多个apk存储到一个文件夹下的情况
            // 下面有介绍
            parsed = parseClusterPackage(packageFile, flags);
        } else {
            // 如果是文件调用 parseMonolithicPackage
            // 下面有介绍
            parsed = parseMonolithicPackage(packageFile, flags);
        }

        long cacheTime = LOG_PARSE_TIMINGS ? SystemClock.uptimeMillis() : 0;
        // 缓存结果
        cacheResult(packageFile, flags, parsed);
        // 打 Log
        if (LOG_PARSE_TIMINGS) {
            parseTime = cacheTime - parseTime;
            cacheTime = SystemClock.uptimeMillis() - cacheTime;
            if (parseTime + cacheTime > LOG_PARSE_TIMINGS_THRESHOLD_MS) {
                Slog.i(TAG, "Parse times for '" + packageFile + "': parse=" + parseTime
                        + "ms, update_cache=" + cacheTime + " ms");
            }
        }
        return parsed;
    }

接下来看解析文件夹的代码
主要功能就是解析文件夹查找到核心 apk 然后继续解析非核心apk，可以没有非核心apk，然后把解析的信息封装到Package中返回。

复制代码

private Package parseClusterPackage(File packageDir, int flags) throws PackageParserException {
        // 通过解析packageDir下所有的文件，找到 baseApk（核心apk） 如果没有baseAPK则会失败；
        // 返回的PackageLite 存储了APK对应的信息，如版本号、版本名、源码路径等。如果成功一定会有核心apk也就是baseAPk
        final PackageLite lite = parseClusterPackageLite(packageDir, 0);
        // 如果处理核心应用但是不是核心应用则退出
        if (mOnlyCoreApps && !lite.coreApp) {
            throw new PackageParserException(INSTALL_PARSE_FAILED_MANIFEST_MALFORMED,
                    "Not a coreApp: " + packageDir);
        }

// Build the split dependency tree.
        SparseArray<int[]> splitDependencies = null;
        final SplitAssetLoader assetLoader;
        // 判断是需要多个apk组成的的还是单独的apk 获取到 assetLoader  splitNames是解析时存储下来的所有apk名称
        if (lite.isolatedSplits && !ArrayUtils.isEmpty(lite.splitNames)) {
            try {
                splitDependencies = SplitAssetDependencyLoader.createDependenciesFromPackage(lite);
                assetLoader = new SplitAssetDependencyLoader(lite, splitDependencies, flags);
            } catch (SplitAssetDependencyLoader.IllegalDependencyException e) {
                throw new PackageParserException(INSTALL_PARSE_FAILED_BAD_MANIFEST, e.getMessage());
            }
        } else {
            assetLoader = new DefaultSplitAssetLoader(lite, flags);
        }

try {
            // 通过 assetLoader 获取到 AssetManager（资源管理类）
            final AssetManager assets = assetLoader.getBaseAssetManager();
            // 通过解析后的路径解析核心 apk
            final File baseApk = new File(lite.baseCodePath);
            // 解析核心 apk ：如解析 AndroidManifest.xml 和 Resources 信息 存储到 Package 对象中
            final Package pkg = parseBaseApk(baseApk, assets, flags);
            // 解析失败证明 apk文件有问题
            if (pkg == null) {
                throw new PackageParserException(INSTALL_PARSE_FAILED_NOT_APK,
                        "Failed to parse base APK: " + baseApk);
            }
            // 如果是多个apk组成的
            if (!ArrayUtils.isEmpty(lite.splitNames)) {
                // 一共有多少个apk
                final int num = lite.splitNames.length;
                // 给 pkg赋值各种对应的属性
                pkg.splitNames = lite.splitNames;
                pkg.splitCodePaths = lite.splitCodePaths;
                pkg.splitRevisionCodes = lite.splitRevisionCodes;
                pkg.splitFlags = new int[num];
                pkg.splitPrivateFlags = new int[num];
                pkg.applicationInfo.splitNames = pkg.splitNames;
                pkg.applicationInfo.splitDependencies = splitDependencies;
                pkg.applicationInfo.splitClassLoaderNames = new String[num];

for (int i = 0; i < num; i++) {
                    final AssetManager splitAssets = assetLoader.getSplitAssetManager(i);
                    // 分别解析每个非核心 apk 信息存储到 pkg 中
                    parseSplitApk(pkg, i, splitAssets, flags);
                }
            }

pkg.setCodePath(packageDir.getCanonicalPath());
            pkg.setUse32bitAbi(lite.use32bitAbi);
            // 最后返回解析的信息 Package
            return pkg;
        } catch (IOException e) {
            throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
                    "Failed to get path: " + lite.baseCodePath, e);
        } finally {
            IoUtils.closeQuietly(assetLoader);
        }
    }

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    private Package parseClusterPackage(File packageDir, int flags) throws PackageParserException {
        // 通过解析packageDir下所有的文件，找到 baseApk（核心apk） 如果没有baseAPK则会失败；
        // 返回的PackageLite 存储了APK对应的信息，如版本号、版本名、源码路径等。如果成功一定会有核心apk也就是baseAPk
        final PackageLite lite = parseClusterPackageLite(packageDir, 0);
        // 如果处理核心应用但是不是核心应用则退出
        if (mOnlyCoreApps && !lite.coreApp) {
            throw new PackageParserException(INSTALL_PARSE_FAILED_MANIFEST_MALFORMED,
                    "Not a coreApp: " + packageDir);
        }

        // Build the split dependency tree.
        SparseArray<int[]> splitDependencies = null;
        final SplitAssetLoader assetLoader;
        // 判断是需要多个apk组成的的还是单独的apk 获取到 assetLoader  splitNames是解析时存储下来的所有apk名称
        if (lite.isolatedSplits && !ArrayUtils.isEmpty(lite.splitNames)) {
            try {
                splitDependencies = SplitAssetDependencyLoader.createDependenciesFromPackage(lite);
                assetLoader = new SplitAssetDependencyLoader(lite, splitDependencies, flags);
            } catch (SplitAssetDependencyLoader.IllegalDependencyException e) {
                throw new PackageParserException(INSTALL_PARSE_FAILED_BAD_MANIFEST, e.getMessage());
            }
        } else {
            assetLoader = new DefaultSplitAssetLoader(lite, flags);
        }

        try {
            // 通过 assetLoader 获取到 AssetManager（资源管理类）
            final AssetManager assets = assetLoader.getBaseAssetManager();
            // 通过解析后的路径解析核心 apk
            final File baseApk = new File(lite.baseCodePath);
            // 解析核心 apk ：如解析 AndroidManifest.xml 和 Resources 信息 存储到 Package 对象中
            final Package pkg = parseBaseApk(baseApk, assets, flags);
            // 解析失败证明 apk文件有问题
            if (pkg == null) {
                throw new PackageParserException(INSTALL_PARSE_FAILED_NOT_APK,
                        "Failed to parse base APK: " + baseApk);
            }
            // 如果是多个apk组成的
            if (!ArrayUtils.isEmpty(lite.splitNames)) {
                // 一共有多少个apk
                final int num = lite.splitNames.length;
                // 给 pkg赋值各种对应的属性
                pkg.splitNames = lite.splitNames;
                pkg.splitCodePaths = lite.splitCodePaths;
                pkg.splitRevisionCodes = lite.splitRevisionCodes;
                pkg.splitFlags = new int[num];
                pkg.splitPrivateFlags = new int[num];
                pkg.applicationInfo.splitNames = pkg.splitNames;
                pkg.applicationInfo.splitDependencies = splitDependencies;
                pkg.applicationInfo.splitClassLoaderNames = new String[num];

                for (int i = 0; i < num; i++) {
                    final AssetManager splitAssets = assetLoader.getSplitAssetManager(i);
                    // 分别解析每个非核心 apk 信息存储到 pkg 中
                    parseSplitApk(pkg, i, splitAssets, flags);
                }
            }

            pkg.setCodePath(packageDir.getCanonicalPath());
            pkg.setUse32bitAbi(lite.use32bitAbi);
            // 最后返回解析的信息 Package
            return pkg;
        } catch (IOException e) {
            throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
                    "Failed to get path: " + lite.baseCodePath, e);
        } finally {
            IoUtils.closeQuietly(assetLoader);
        }
    }

接下来看另外一个分支，如果不是文件夹走 parseMonolithicPackage() 方法。
这个方法内部比较简单和上面解析文件夹的流程大体相同代码也很少，最后也是返回了 Package 对象。

复制代码

public Package parseMonolithicPackage(File apkFile, int flags) throws PackageParserException {
        // parseMonolithicPackageLite 代码很少 
        // 其内部和上面解析文件夹一样 调用了 parseApkLite() 进行初步解析返回了 PackageLite 对象。
        final PackageLite lite = parseMonolithicPackageLite(apkFile, flags);
        if (mOnlyCoreApps) {
            if (!lite.coreApp) {
                throw new PackageParserException(INSTALL_PARSE_FAILED_MANIFEST_MALFORMED,
                        "Not a coreApp: " + apkFile);
            }
        }
        // 直接创建 DefaultSplitAssetLoader 
        final SplitAssetLoader assetLoader = new DefaultSplitAssetLoader(lite, flags);
        try {
            // 一样调用了 parseBaseApk 解析apk文件 AndroidManifest.xml 等信息返回 Package 对象
            final Package pkg = parseBaseApk(apkFile, assetLoader.getBaseAssetManager(), flags);
            pkg.setCodePath(apkFile.getCanonicalPath());
            pkg.setUse32bitAbi(lite.use32bitAbi);
            // 返回 Package 对象
            return pkg;
        } catch (IOException e) {
            throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
                    "Failed to get path: " + apkFile, e);
        } finally {
            IoUtils.closeQuietly(assetLoader);
        }
    }

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    public Package parseMonolithicPackage(File apkFile, int flags) throws PackageParserException {
        // parseMonolithicPackageLite 代码很少 
        // 其内部和上面解析文件夹一样 调用了 parseApkLite() 进行初步解析返回了 PackageLite 对象。
        final PackageLite lite = parseMonolithicPackageLite(apkFile, flags);
        if (mOnlyCoreApps) {
            if (!lite.coreApp) {
                throw new PackageParserException(INSTALL_PARSE_FAILED_MANIFEST_MALFORMED,
                        "Not a coreApp: " + apkFile);
            }
        }
        // 直接创建 DefaultSplitAssetLoader 
        final SplitAssetLoader assetLoader = new DefaultSplitAssetLoader(lite, flags);
        try {
            // 一样调用了 parseBaseApk 解析apk文件 AndroidManifest.xml 等信息返回 Package 对象
            final Package pkg = parseBaseApk(apkFile, assetLoader.getBaseAssetManager(), flags);
            pkg.setCodePath(apkFile.getCanonicalPath());
            pkg.setUse32bitAbi(lite.use32bitAbi);
            // 返回 Package 对象
            return pkg;
        } catch (IOException e) {
            throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
                    "Failed to get path: " + apkFile, e);
        } finally {
            IoUtils.closeQuietly(assetLoader);
        }
    }

到这里基本上解析apk的流程就差不多了。接下来就是安装应用了

最后

以上就是曾经龙猫最近收集整理的关于关于 PackageManagerService的全部内容，更多相关关于内容请搜索靠谱客的其他文章。

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本文分类：Android
浏览次数：175 次浏览
发布日期：2024-01-15 05:15:47
本文链接：https://www.kaopuke.com/article/k-p-k_13_u_23_ogf3_13__7__18_5.html

关于 PackageManagerService

文章目录

了解 PackageManagerService

了解 pm/Settings.java

服务初始化过程

处理 permission 文件

扫描应用目录的过程

当发出 Intent 时，如果系统中应用有多个相应，会弹出一个对话框让你选择？

解析 APK

最后

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关于 PackageManagerService

文章目录

了解 PackageManagerService

了解 pm/Settings.java

服务初始化过程

处理 permission 文件

扫描应用目录的过程

当发出 Intent 时，如果系统中应用有多个相应，会弹出一个对话框让你选择？

解析 APK

最后

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