Android应用程序安装过程源代码分析

        Android系统在启动的过程中，会启动一个应用程序管理服务PackageManagerService，这个服务负责扫描系统中特定的目录，找到里面的应用程序文件，即以Apk为后缀的文件，然后对这些文件进解析，得到应用程序的相关信息，完成应用程序的安装过程，本文将详细分析这个过程。

        应用程序管理服务PackageManagerService安装应用程序的过程，其实就是解析析应用程序配置文件AndroidManifest.xml的过程，并从里面得到得到应用程序的相关信息，例如得到应用程序的组件Activity、Service、Broadcast Receiver和Content Provider等信息，有了这些信息后，通过ActivityManagerService这个服务，我们就可以在系统中正常地使用这些应用程序了。

        应用程序管理服务PackageManagerService是系统启动的时候由SystemServer组件启动的，启后它就会执行应用程序安装的过程，因此，本文将从SystemServer启动PackageManagerService服务的过程开始分析系统中的应用程序安装的过程。

        应用程序管理服务PackageManagerService从启动到安装应用程序的过程如下图所示：

        下面我们具体分析每一个步骤。

        Step 1. SystemServer.main

        这个函数定义在frameworks/base/services/java/com/android/server/SystemServer.java文件中：

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

        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。

        Step 2. SystemServer.init1

        这个函数是一个JNI方法，实现在 frameworks/base/services/jni/com_android_server_SystemServer.cpp文件中：

namespace android {extern "C" int system_init();static void android_server_SystemServer_init1(JNIEnv* env, jobject clazz){    system_init();}/* * JNI registration. */static JNINativeMethod gMethods[] = {    /* name, signature, funcPtr */    { "init1", "([Ljava/lang/String;)V", (void*) android_server_SystemServer_init1 },};int register_android_server_SystemServer(JNIEnv* env){    return jniRegisterNativeMethods(env, "com/android/server/SystemServer",            gMethods, NELEM(gMethods));}}; // namespace android

        这个函数很简单，只是调用了system_init函数来进一步执行操作。

        Step 3. libsystem_server.system_init

        函数system_init实现在libsystem_server库中，源代码位于frameworks/base/cmds/system_server/library/system_init.cpp文件中：

extern "C" status_t system_init(){LOGI("Entered system_init()");sp<ProcessState> proc(ProcessState::self());sp<IServiceManager> sm = defaultServiceManager();LOGI("ServiceManager: %p\n", sm.get());sp<GrimReaper> 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 SurfaceFlingerSurfaceFlinger::instantiate();}// Start the sensor serviceSensorService::instantiate();// On the simulator, audioflinger et al don't get started the// same way as on the device, and we need to start them hereif (!proc->supportsProcesses()) {// Start the AudioFlingerAudioFlinger::instantiate();// Start the media playback serviceMediaPlayerService::instantiate();// Start the camera serviceCameraService::instantiate();// Start the audio policy serviceAudioPolicyService::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;}

        这个函数首先会初始化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。关于这个AndroidRuntime实例变量runtime的相关资料，可能参考前面一篇文章Android应用程序进程启动过程的源代码分析一文。

        Step 4. AndroidRuntime.callStatic

        这个函数定义在frameworks/base/core/jni/AndroidRuntime.cpp文件中：

/** Call a static Java Programming Language function that takes no arguments and returns void.*/status_t AndroidRuntime::callStatic(const char* className, const char* methodName){JNIEnv* env;jclass clazz;jmethodID methodId;env = getJNIEnv();if (env == NULL)return UNKNOWN_ERROR;clazz = findClass(env, className);if (clazz == NULL) {LOGE("ERROR: could not find class '%s'\n", className);return UNKNOWN_ERROR;}methodId = env->GetStaticMethodID(clazz, methodName, "()V");if (methodId == NULL) {LOGE("ERROR: could not find method %s.%s\n", className, methodName);return UNKNOWN_ERROR;}env->CallStaticVoidMethod(clazz, methodId);return NO_ERROR;}

        这个函数调用由参数className指定的java类的静态成员函数，这个静态成员函数是由参数methodName指定的。上面传进来的参数className的值为"com/android/server/SystemServer"，而参数methodName的值为"init2"，因此，接下来就会调用SystemServer类的init2函数了。

        Step 5. SystemServer.init2

        这个函数定义在frameworks/base/services/java/com/android/server/SystemServer.java文件中：

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();}}

        这个函数创建了一个ServerThread线程，PackageManagerService服务就是这个线程中启动的了。这里调用了ServerThread实例thr的start函数之后，下面就会执行这个实例的run函数了。

        Step 6. ServerThread.run

        这个函数定义在frameworks/base/services/java/com/android/server/SystemServer.java文件中：

class ServerThread extends Thread {......@Overridepublic 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);}......}......}

        这个函数除了启动PackageManagerService服务之外，还启动了其它很多的服务，例如在前面学习Activity和Service的几篇文章中经常看到的ActivityManagerService服务，有兴趣的读者可以自己研究一下。

        Step 7. PackageManagerService.main

        这个函数定义在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：

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;}......}

        这个函数创建了一个PackageManagerService服务实例，然后把这个服务添加到ServiceManager中去，ServiceManager是Android系统Binder进程间通信机制的守护进程，负责管理系统中的Binder对象，具体可以参考浅谈Service Manager成为Android进程间通信（IPC）机制Binder守护进程之路一文。
        在创建这个PackageManagerService服务实例时，会在PackageManagerService类的构造函数中开始执行安装应用程序的过程：

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);......}}}......}

        这里会调用scanDirLI函数来扫描移动设备上的下面这五个目录中的Apk文件：

        /system/framework

        /system/app

        /vendor/app

        /data/app

        /data/app-private

       Step 8. PackageManagerService.scanDirLI
       这个函数定义在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：

class PackageManagerService extends IPackageManager.Stub {......private void scanDirLI(File dir, int flags, int scanMode, long currentTime) {String[] files = dir.list();......int i;for (i=0; i<files.length; i++) {File file = new File(dir, files[i]);if (!isPackageFilename(files[i])) {// Ignore entries which are not apk'scontinue;}PackageParser.Package pkg = scanPackageLI(file,flags|PackageParser.PARSE_MUST_BE_APK, scanMode, currentTime);// Don't mess around with apps in system partition.if (pkg == null && (flags & PackageParser.PARSE_IS_SYSTEM) == 0 &&mLastScanError == PackageManager.INSTALL_FAILED_INVALID_APK) {// Delete the apkSlog.w(TAG, "Cleaning up failed install of " + file);file.delete();}}}......}

         对于目录中的每一个文件，如果是以后Apk作为后缀名，那么就调用scanPackageLI函数来对它进行解析和安装。

         Step 9. PackageManagerService.scanPackageLI

         这个函数定义在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：

class PackageManagerService extends IPackageManager.Stub {......private PackageParser.Package scanPackageLI(File scanFile,int parseFlags, int scanMode, long currentTime) {......String scanPath = scanFile.getPath();parseFlags |= mDefParseFlags;PackageParser pp = new PackageParser(scanPath);......final PackageParser.Package pkg = pp.parsePackage(scanFile,scanPath, mMetrics, parseFlags);......return scanPackageLI(pkg, parseFlags, scanMode | SCAN_UPDATE_SIGNATURE, currentTime);}......}

        这个函数首先会为这个Apk文件创建一个PackageParser实例，接着调用这个实例的parsePackage函数来对这个Apk文件进行解析。这个函数最后还会调用另外一个版本的scanPackageLI函数把来解析后得到的应用程序信息保存在PackageManagerService中。

        Step 10. PackageParser.parsePackage
        这个函数定义在frameworks/base/core/java/android/content/pm/PackageParser.java文件中：

public class PackageParser {......public Package parsePackage(File sourceFile, String destCodePath,DisplayMetrics metrics, int flags) {......mArchiveSourcePath = sourceFile.getPath();......XmlResourceParser parser = null;AssetManager assmgr = null;boolean assetError = true;try {assmgr = new AssetManager();int cookie = assmgr.addAssetPath(mArchiveSourcePath);if(cookie != 0) {parser = assmgr.openXmlResourceParser(cookie, "AndroidManifest.xml");assetError = false;} else {......}} catch (Exception e) {......}......String[] errorText = new String[1];Package pkg = null;Exception errorException = null;try {// XXXX todo: need to figure out correct configuration.Resources res = new Resources(assmgr, metrics, null);pkg = parsePackage(res, parser, flags, errorText);} catch (Exception e) {......}......parser.close();assmgr.close();// Set code and resource pathspkg.mPath = destCodePath;pkg.mScanPath = mArchiveSourcePath;//pkg.applicationInfo.sourceDir = destCodePath;//pkg.applicationInfo.publicSourceDir = destRes;pkg.mSignatures = null;return pkg;}......}

        每一个Apk文件都是一个归档文件，它里面包含了Android应用程序的配置文件AndroidManifest.xml，这里主要就是要对这个配置文件就行解析了，从Apk归档文件中得到这个配置文件后，就调用另一外版本的parsePackage函数对这个应用程序进行解析了：

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;}......}

        这里就是对AndroidManifest.xml文件中的各个标签进行解析了，各个标签的含义可以参考官方文档http://developer.android.com/guide/topics/manifest/manifest-intro.html，这里我们只简单看一下application标签的解析，这是通过调用parseApplication函数来进行的。

        Step 11. PackageParser.parseApplication
        这个函数定义在frameworks/base/core/java/android/content/pm/PackageParser.java文件中：

public class PackageParser {......private boolean parseApplication(Package owner, Resources res,XmlPullParser parser, AttributeSet attrs, int flags, String[] outError)throws XmlPullParserException, IOException {final ApplicationInfo ai = owner.applicationInfo;final String pkgName = owner.applicationInfo.packageName;TypedArray sa = res.obtainAttributes(attrs,com.android.internal.R.styleable.AndroidManifestApplication);......int type;while ((type=parser.next()) != parser.END_DOCUMENT&& (type != parser.END_TAG || parser.getDepth() > innerDepth)) {if (type == parser.END_TAG || type == parser.TEXT) {continue;}String tagName = parser.getName();if (tagName.equals("activity")) {Activity a = parseActivity(owner, res, parser, attrs, flags, outError, false);......owner.activities.add(a);} else if (tagName.equals("receiver")) {Activity a = parseActivity(owner, res, parser, attrs, flags, outError, true);......owner.receivers.add(a);} else if (tagName.equals("service")) {Service s = parseService(owner, res, parser, attrs, flags, outError);......owner.services.add(s);} else if (tagName.equals("provider")) {Provider p = parseProvider(owner, res, parser, attrs, flags, outError);......owner.providers.add(p);} else if (tagName.equals("activity-alias")) {Activity a = parseActivityAlias(owner, res, parser, attrs, flags, outError);......owner.activities.add(a);} else if (parser.getName().equals("meta-data")) {......} else if (tagName.equals("uses-library")) {......} else if (tagName.equals("uses-package")) {......} else {......}}return true;}......}

        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，各个标签的含义可以参考官方文档http://developer.android.com/guide/topics/manifest/manifest-intro.html。

        这里解析完成后，一层层返回到Step 9中，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。

        Step 12. PackageManagerService.scanPackageLI

        这个函数定义在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：

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<String, PackageParser.Package> mPackages =new HashMap<String, PackageParser.Package>();......// 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<ComponentName, PackageParser.Provider> mProvidersByComponent =new HashMap<ComponentName, PackageParser.Provider>();......private PackageParser.Package scanPackageLI(PackageParser.Package pkg,int parseFlags, int scanMode, long currentTime) {......synchronized (mPackages) {......// Add the new setting to mPackagesmPackages.put(pkg.applicationInfo.packageName, pkg);......int N = pkg.providers.size();int i;for (i=0; i<N; i++) {PackageParser.Provider p = pkg.providers.get(i);p.info.processName = fixProcessName(pkg.applicationInfo.processName,p.info.processName, pkg.applicationInfo.uid);mProvidersByComponent.put(new ComponentName(p.info.packageName,p.info.name), p);......}N = pkg.services.size();for (i=0; i<N; i++) {PackageParser.Service s = pkg.services.get(i);s.info.processName = fixProcessName(pkg.applicationInfo.processName,s.info.processName, pkg.applicationInfo.uid);mServices.addService(s);......}N = pkg.receivers.size();r = null;for (i=0; i<N; i++) {PackageParser.Activity a = pkg.receivers.get(i);a.info.processName = fixProcessName(pkg.applicationInfo.processName,a.info.processName, pkg.applicationInfo.uid);mReceivers.addActivity(a, "receiver");......}N = pkg.activities.size();for (i=0; i<N; i++) {PackageParser.Activity a = pkg.activities.get(i);a.info.processName = fixProcessName(pkg.applicationInfo.processName,a.info.processName, pkg.applicationInfo.uid);mActivities.addActivity(a, "activity");......}......}......return pkg;}......}

        这个函数主要就是把前面解析应用程序得到的package、provider、service、receiver和activity等信息保存在PackageManagerService服务中了。

        这样，在Android系统启动的时候安装应用程序的过程就介绍完了，但是，这些应用程序只是相当于在PackageManagerService服务注册好了，如果我们想要在Android桌面上看到这些应用程序，还需要有一个Home应用程序，负责从PackageManagerService服务中把这些安装好的应用程序取出来，并以友好的方式在桌面上展现出来，例如以快捷图标的形式。在Android系统中，负责把系统中已经安装的应用程序在桌面中展现出来的Home应用程序就是Launcher了，在下一篇文章中，我们将介绍Launcher是如何启动的以及它是如何从PackageManagerService服务中把系统中已经安装好的应用程序展现出来的，敬请期待。

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