Android应用框架之PackageManagerService-白红宇

系统在启动的时候会启动一个叫做PackageManagerService的服务，顾名思义，这个服务主要管理安装在设备上的应用程序，其中最为重要的工作就是在在系统启动之后，PackageManagerService会扫描特定目录下地以apk为后缀的文件，然后将对应的应用安装到系统中。注意，这里的安装并不是我们平时所说的安装，它指的的是将存放在磁盘之上的静态应用程序文件进行解析，并将相关信息注册到系统中。而具体的解析工作实际就是读取应用的配置文件manifest.xml，并将文件中配置的组件

（Activity,Service,BroadcastRecevier,ContentProvider），权限等信息注册到PackageManagerService中。

本篇博客主要介绍PackageManagerService的启动过程，以及PackageManagerService如何安装各个应用程序。

1.`PackageManagerService`启动过程

和ActivityManagerService，WindowManagerService一样，PackageManagerService是一个系统级的服务，运行在独立的进程中，而所有的系统级服务都是由SystemServer启动的。所以首先来看看SystemServer的启动过程。

1) `SystemServer`启动：

SystemServer组件是由Zygote进程负责启动的，启动的时候就会调用它的main函数，这个函数主要调用了JNI方法init1来做一些系统初始化的工作。

public class SystemServer{    ......    native public static void init1(String[] args);    ......    public static void main(String[] args) {        ......        init1(args);        ......    }    ......}

2)`SystemServer.system_init`

经过一系列调用后转到system_init方法，这是一个JNI方法

extern "C" status_t system_init(){    LOGI("Entered system_init()");    sp
     
       proc(ProcessState::self());    sp
      
        sm = defaultServiceManager();    LOGI("ServiceManager: %p\n", sm.get());    sp
       
         grim = new GrimReaper();    sm->asBinder()->linkToDeath(grim, grim.get(), 0);    char propBuf[PROPERTY_VALUE_MAX];    property_get("system_init.startsurfaceflinger", propBuf, "1");    if (strcmp(propBuf, "1") == 0) {        // Start the SurfaceFlinger        SurfaceFlinger::instantiate();    }    // Start the sensor service    SensorService::instantiate();    // On the simulator, audioflinger et al don't get started the    // same way as on the device, and we need to start them here    if (!proc->supportsProcesses()) {        // Start the AudioFlinger        AudioFlinger::instantiate();        // Start the media playback service        MediaPlayerService::instantiate();        // Start the camera service        CameraService::instantiate();        // Start the audio policy service        AudioPolicyService::instantiate();    }    // And now start the Android runtime.  We have to do this bit    // of nastiness because the Android runtime initialization requires    // some of the core system services to already be started.    // All other servers should just start the Android runtime at    // the beginning of their processes's main(), before calling    // the init function.    LOGI("System server: starting Android runtime.\n");    AndroidRuntime* runtime = AndroidRuntime::getRuntime();    LOGI("System server: starting Android services.\n");    runtime->callStatic("com/android/server/SystemServer", "init2");    // If running in our own process, just go into the thread    // pool.  Otherwise, call the initialization finished    // func to let this process continue its initilization.    if (proc->supportsProcesses()) {        LOGI("System server: entering thread pool.\n");        ProcessState::self()->startThreadPool();        IPCThreadState::self()->joinThreadPool();        LOGI("System server: exiting thread pool.\n");    }    return NO_ERROR;}

在这个方法中，创建了SurfaceFlinger、SensorService、AudioFlinger、MediaPlayerService、CameraService和AudioPolicyService这几个服务，然后就通过系统全局唯一的AndroidRuntime实例变量runtime的callStatic来调用SystemServer的init2函数了。init2函数很简单，创建一个线程，而PackageManagerService就是在这个线程中创建的。

public class SystemServer{    ......    public static final void init2() {        Slog.i(TAG, "Entered the Android system server!");        Thread thr = new ServerThread();        thr.setName("android.server.ServerThread");        thr.start();    }}

3)ServerThread.run

class ServerThread extends Thread {    ......    @Override    public void run() {        ......        IPackageManager pm = null;        ......        // Critical services...        try {            ......            Slog.i(TAG, "Package Manager");            pm = PackageManagerService.main(context,                        factoryTest != SystemServer.FACTORY_TEST_OFF);            ......        } catch (RuntimeException e) {            Slog.e("System", "Failure starting core service", e);        }        ......    }    ......}

在这个线程中创建了PackageManagerService,并同时启动了其main函数。另外在这个线程中还启动了ActivityManagerService等其他Service

2.应用安装

接下来再来看看PackageManagerService启动之后如何进行应用程序的安装。

1）`PackageManagerService.main`

class PackageManagerService extends IPackageManager.Stub {
         ......    public static final IPackageManager main(Context context, boolean factoryTest) {        PackageManagerService m = new PackageManagerService(context, factoryTest);        ServiceManager.addService("package", m);        return m;    }    ......}

可以看到，创建完成后，就加载到ServiceManager中。接下来看看PackageManagerService的构造函数：

class PackageManagerService extends IPackageManager.Stub {
         ......    public PackageManagerService(Context context, boolean factoryTest) {        ......        synchronized (mInstallLock) {            synchronized (mPackages) {                ......                File dataDir = Environment.getDataDirectory();                mAppDataDir = new File(dataDir, "data");                mSecureAppDataDir = new File(dataDir, "secure/data");                mDrmAppPrivateInstallDir = new File(dataDir, "app-private");                ......                mFrameworkDir = new File(Environment.getRootDirectory(), "framework");                mDalvikCacheDir = new File(dataDir, "dalvik-cache");                ......                // Find base frameworks (resource packages without code).                mFrameworkInstallObserver = new AppDirObserver(                mFrameworkDir.getPath(), OBSERVER_EVENTS, true);                mFrameworkInstallObserver.startWatching();                scanDirLI(mFrameworkDir, PackageParser.PARSE_IS_SYSTEM                    | PackageParser.PARSE_IS_SYSTEM_DIR,                    scanMode | SCAN_NO_DEX, 0);                // Collect all system packages.                mSystemAppDir = new File(Environment.getRootDirectory(), "app");                mSystemInstallObserver = new AppDirObserver(                    mSystemAppDir.getPath(), OBSERVER_EVENTS, true);                mSystemInstallObserver.startWatching();                scanDirLI(mSystemAppDir, PackageParser.PARSE_IS_SYSTEM                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);                // Collect all vendor packages.                mVendorAppDir = new File("/vendor/app");                mVendorInstallObserver = new AppDirObserver(                    mVendorAppDir.getPath(), OBSERVER_EVENTS, true);                mVendorInstallObserver.startWatching();                scanDirLI(mVendorAppDir, PackageParser.PARSE_IS_SYSTEM                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);                mAppInstallObserver = new AppDirObserver(                    mAppInstallDir.getPath(), OBSERVER_EVENTS, false);                mAppInstallObserver.startWatching();                scanDirLI(mAppInstallDir, 0, scanMode, 0);                mDrmAppInstallObserver = new AppDirObserver(                    mDrmAppPrivateInstallDir.getPath(), OBSERVER_EVENTS, false);                mDrmAppInstallObserver.startWatching();                scanDirLI(mDrmAppPrivateInstallDir, PackageParser.PARSE_FORWARD_LOCK,                    scanMode, 0);                ......            }        }    }    ......}

可以看到，在构造函数中，PackageManagerService(PMS)会扫描特定目录下的APK文件，然后进行相关的加载工作，这些目录包括：

/system/framework
/system/app
/vendor/app
/data/app
/data/app-private

在每个路径下，都调用了scanDirLI函数，接下来看看对应的函数做了些什么。

2）`PackageParser.parsePackage`

scanDirLI中又经过多次调用，具体就是扫描对应目录的文件，如果是apk文件，就找到apk文件中的manifest文件，最后再为每一个apk创建一个PackageParser对象，并将manifest文件传递给PackageParser.parsePackage。

public class PackageParser {    ......    private Package parsePackage(            Resources res, XmlResourceParser parser, int flags, String[] outError)            throws XmlPullParserException, IOException {        ......        String pkgName = parsePackageName(parser, attrs, flags, outError);        ......        final Package pkg = new Package(pkgName);        ......        int type;        ......        TypedArray sa = res.obtainAttributes(attrs,            com.android.internal.R.styleable.AndroidManifest);        ......        while ((type=parser.next()) != parser.END_DOCUMENT            && (type != parser.END_TAG || parser.getDepth() > outerDepth)) {                if (type == parser.END_TAG || type == parser.TEXT) {                    continue;                }                String tagName = parser.getName();                if (tagName.equals("application")) {                    ......                    if (!parseApplication(pkg, res, parser, attrs, flags, outError)) {                        return null;                    }                } else if (tagName.equals("permission-group")) {                    ......                } else if (tagName.equals("permission")) {                    ......                } else if (tagName.equals("permission-tree")) {                    ......                } else if (tagName.equals("uses-permission")) {                    ......                } else if (tagName.equals("uses-configuration")) {                    ......                } else if (tagName.equals("uses-feature")) {                    ......                } else if (tagName.equals("uses-sdk")) {                    ......                } else if (tagName.equals("supports-screens")) {                    ......                } else if (tagName.equals("protected-broadcast")) {                    ......                } else if (tagName.equals("instrumentation")) {                    ......                } else if (tagName.equals("original-package")) {                    ......                } else if (tagName.equals("adopt-permissions")) {                    ......                } else if (tagName.equals("uses-gl-texture")) {                    ......                } else if (tagName.equals("compatible-screens")) {                    ......                } else if (tagName.equals("eat-comment")) {                    ......                } else if (RIGID_PARSER) {                    ......                } else {                    ......                }        }        ......        return pkg;    }    ......        private Package parsePackage(            Resources res, XmlResourceParser parser, int flags, String[] outError)            throws XmlPullParserException, IOException {        ......        String pkgName = parsePackageName(parser, attrs, flags, outError);        ......        final Package pkg = new Package(pkgName);        ......        int type;        ......        TypedArray sa = res.obtainAttributes(attrs,            com.android.internal.R.styleable.AndroidManifest);        ......        while ((type=parser.next()) != parser.END_DOCUMENT            && (type != parser.END_TAG || parser.getDepth() > outerDepth)) {                if (type == parser.END_TAG || type == parser.TEXT) {                    continue;                }                String tagName = parser.getName();                if (tagName.equals("application")) {                    ......                    if (!parseApplication(pkg, res, parser, attrs, flags, outError)) {                        return null;                    }                } else if (tagName.equals("permission-group")) {                    ......                } else if (tagName.equals("permission")) {                    ......                } else if (tagName.equals("permission-tree")) {                    ......                } else if (tagName.equals("uses-permission")) {                    ......                } else if (tagName.equals("uses-configuration")) {                    ......                } else if (tagName.equals("uses-feature")) {                    ......                } else if (tagName.equals("uses-sdk")) {                    ......                } else if (tagName.equals("supports-screens")) {                    ......                } else if (tagName.equals("protected-broadcast")) {                    ......                } else if (tagName.equals("instrumentation")) {                    ......                } else if (tagName.equals("original-package")) {                    ......                } else if (tagName.equals("adopt-permissions")) {                    ......                } else if (tagName.equals("uses-gl-texture")) {                    ......                } else if (tagName.equals("compatible-screens")) {                    ......                } else if (tagName.equals("eat-comment")) {                    ......                } else if (RIGID_PARSER) {                    ......                } else {                    ......                }        }        ......        return pkg;    }    ......}

这里就是对AndroidManifest.xml文件中的application标签进行解析了，我们常用到的标签就有activity、service、receiver和provider，这里解析完成后，一层层返回，调用另一个版本的scanPackageLI函数把来解析后得到的应用程序信息保存下来。

class PackageManagerService extends IPackageManager.Stub {    ......    // Keys are String (package name), values are Package.  This also serves    // as the lock for the global state.  Methods that must be called with    // this lock held have the prefix "LP".    final HashMap
     
       mPackages =        new HashMap
      
       ();    ......    // All available activities, for your resolving pleasure.    final ActivityIntentResolver mActivities =    new ActivityIntentResolver();    // All available receivers, for your resolving pleasure.    final ActivityIntentResolver mReceivers =        new ActivityIntentResolver();    // All available services, for your resolving pleasure.    final ServiceIntentResolver mServices = new ServiceIntentResolver();    // Keys are String (provider class name), values are Provider.    final HashMap
       
         mProvidersByComponent =        new HashMap
        
         ();    ......    private PackageParser.Package scanPackageLI(PackageParser.Package pkg,            int parseFlags, int scanMode, long currentTime) {        ......        synchronized (mPackages) {            ......            // Add the new setting to mPackages            mPackages.put(pkg.applicationInfo.packageName, pkg);            ......            int N = pkg.providers.size();            int i;            for (i=0; i

到这里整个应用的安装过程就介绍完了。其实整个过程还是很明确，清晰的。

接下来再来总结一下整个启动过程：

Zygote—>启动SystemServer—>启动ServerThread—>启动PackageManagerService—>扫描特定目录下的apk文件，进行加载—>解析APK的manifest文件，将配置信息加载到PackageManagerService中

1.PackageManagerService启动过程

1) SystemServer启动：

2)SystemServer.system_init