Android 启动时应用的安装解析过程《一》

应用对于Android系统来说至关重要，系统会有几个时机对APP进行解析，一个是APK安装的时候会进行解析，还有一个就是系统在重启之后会进行解析，这里就简单的记录一下重启的时候APK的解析过程。

一、SystemServer

系统在启动之后从内核层启动第一个用户控件Init进程，再通过Init进程启动系统中第一个java 进程zygote，随之zygote fock出SystemServer，SystemServer再开始启动一些列系统服务，其中就包括PackageMangerService，在startBootstrapServices函数中：

public final void startBootstrapServices(TimingsTraceAndSlog timingsTraceAndSlog) {
   
.....
    // 先调用了PackageManagerService的main函数
 	Pair<PackageManagerService, IPackageManager> main = PackageManagerService.main(context, installer, domainVerificationService, z, this.mOnlyCore);
 	// main 函数创建了PackageManagerService 和IPackageManager 的实例
    this.mPackageManagerService = (PackageManagerService) main.first;
    IPackageManager iPackageManager = (IPackageManager) main.second;
    Watchdog.getInstance().resumeWatchingCurrentThread("packagemanagermain");
    // 该方法将在 BaseDexClassLoader 中安装一个报告器，同时还将强制报告系统服务器已加载的任何 dex 文件
    SystemServerDexLoadReporter.configureSystemServerDexReporter(iPackageManager);
    this.mFirstBoot = this.mPackageManagerService.isFirstBoot();
    this.mPackageManager = this.mSystemContext.getPackageManager();

二、PackageManagerService

在SystemServer中是先调用PackageManagerService的main函数来初始化它自己的，来看看它做了什么：

public static Pair<PackageManagerService, IPackageManager> main(Context context,
            Installer installer, @NonNull DomainVerificationService domainVerificationService,
            boolean factoryTest, boolean onlyCore) {
   
		PackageManagerServiceCompilerMapping.checkProperties();
        final TimingsTraceAndSlog t = new TimingsTraceAndSlog(TAG + "Timing",
                Trace.TRACE_TAG_PACKAGE_MANAGER);
        t.traceBegin("create package manager");
        final PackageManagerTracedLock lock = new PackageManagerTracedLock();
        final Object installLock = new Object();
        // 创建自带handler的线程
        HandlerThread backgroundThread = new ServiceThread("PackageManagerBg",
                Process.THREAD_PRIORITY_BACKGROUND, true /*allowIo*/);
        backgroundThread.start();
        Handler backgroundHandler = new Handler(backgroundThread.getLooper());
        // 创建PackageManagerServiceInjector 用来持有管理其他一系列重要的类实例
		PackageManagerServiceInjector injector = new PackageManagerServiceInjector(
                context, lock, installer, installLock, new PackageAbiHelperImpl(),
                backgroundHandler,
                SYSTEM_PARTITIONS,
                // 解析compnent的
                (i, pm) -> new ComponentResolver(i.getUserManagerService(), pm.mUserNeedsBadging),
                // 权限管理服务
                (i, pm) -> PermissionManagerService.create(context,
                        i.getSystemConfig().getAvailableFeatures()),
                // 用户管理服务
                (i, pm) -> new UserManagerService(context, pm,
                        new UserDataPreparer(installer, installLock, context, onlyCore),
                        lock),
               // 系统数据库，用来访问系统数据库的
                (i, pm) -> new Settings(Environment.getDataDirectory(),
                        RuntimePermissionsPersistence.createInstance(),
                        i.getPermissionManagerServiceInternal(),
                        domainVerificationService, backgroundHandler, lock),
                (i, pm) -> AppsFilterImpl.create(i,
                        i.getLocalService(PackageManagerInternal.class)),
                 // compat服务用来管理一些系统特性
                (i, pm) -> (PlatformCompat) ServiceManager.getService("platform_compat"),
                // 系统配置服务，预置的系统的权限、硬件feature还有其他的一些配置在这里面解析
                (i, pm) -> SystemConfig.getInstance(),
                // 在软件包上运行 dexopt 命令的辅助类。
                (i, pm) -> new PackageDexOptimizer(i.getInstaller(), i.getInstallLock(),
                        i.getContext(), "*dexopt*"),
                // dex 行为管理类会保存所有包的dex位置
                (i, pm) -> new DexManager(i.getContext(), i.getPackageDexOptimizer(),
                        i.getInstaller(), i.getInstallLock()),
                (i, pm) -> new ArtManagerService(i.getContext(), i.getInstaller(),
                        i.getInstallLock()),
                (i, pm) -> ApexManager.getInstance(),
                (i, pm) -> new ViewCompiler(i.getInstallLock(), i.getInstaller()),
                (i, pm) -> (IncrementalManager)
                        i.getContext().getSystemService(Context.INCREMENTAL_SERVICE),
                (i, pm) -> new DefaultAppProvider(() -> context.getSystemService(RoleManager.class),
                        () -> LocalServices.getService(UserManagerInternal.class)),
                (i, pm) -> new DisplayMetrics(),
                // 包解析类
                (i, pm