Android應用程序安裝過程源代碼分析 · 老羅的Android之旅（總結）

原文出處——>[Android應用程序安裝過程源代碼分析](http://blog.csdn.net/luoshengyang/article/details/6766010) Android系統在啟動的過程中，會啟動一個應用程序管理服務PackageManagerService，這個服務負責掃描系統中特定的目錄，找到里面的應用程序文件，即以Apk為后綴的文件，然后對這些文件進解析，得到應用程序的相關信息，完成應用程序的安裝過程，本文將詳細分析這個過程。應用程序管理服務PackageManagerService安裝應用程序的過程，其實就是解析析應用程序配置文件AndroidManifest.xml的過程，并從里面得到得到應用程序的相關信息，例如得到應用程序的組件Activity、Service、Broadcast Receiver和Content Provider等信息，有了這些信息后，通過ActivityManagerService這個服務，我們就可以在系統中正常地使用這些應用程序了。應用程序管理服務PackageManagerService是系統啟動的時候由SystemServer組件啟動的，啟后它就會執行應用程序安裝的過程，因此，本文將從SystemServer啟動PackageManagerService服務的過程開始分析系統中的應用程序安裝的過程。應用程序管理服務PackageManagerService從啟動到安裝應用程序的過程如下圖所示： ![](https://box.kancloud.cn/13ff462957a790adb7ab26cc45369cf6_697x768.jpg) 下面我們具體分析每一個步驟。 **Step 1. SystemServer.main** 這個函數定義在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組件是由Zygote進程負責啟動的，啟動的時候就會調用它的main函數，這個函數主要調用了JNI方法init1來做一些系統初始化的工作。 **Step 2. SystemServer.init1** 這個函數是一個JNI方法，實現在 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 ~~~ 這個函數很簡單，只是調用了system_init函數來進一步執行操作。 **Step 3. libsystem_server.system_init** 函數system_init實現在libsystem_server庫中，源代碼位于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 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; } ~~~ 這個函數首先會初始化SurfaceFlinger、SensorService、AudioFlinger、MediaPlayerService、CameraService和AudioPolicyService這幾個服務，然后就通過系統全局唯一的AndroidRuntime實例變量runtime的callStatic來調用SystemServer的init2函數了。關于這個AndroidRuntime實例變量runtime的相關資料，可能參考前面一篇文章Android應用程序進程啟動過程的源代碼分析一文。 **Step 4. AndroidRuntime.callStatic** 這個函數定義在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; } ~~~ 這個函數調用由參數className指定的java類的靜態成員函數，這個靜態成員函數是由參數methodName指定的。上面傳進來的參數className的值為"com/android/server/SystemServer"，而參數methodName的值為"init2"，因此，接下來就會調用SystemServer類的init2函數了。 **Step 5. SystemServer.init2** 這個函數定義在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(); } } ~~~ 這個函數創建了一個ServerThread線程，PackageManagerService服務就是這個線程中啟動的了。這里調用了ServerThread實例thr的start函數之后，下面就會執行這個實例的run函數了。 **Step 6. ServerThread.run** 這個函數定義在frameworks/base/services/java/com/android/server/SystemServer.java文件中： ~~~ 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); } ...... } ...... } ~~~ 這個函數除了啟動PackageManagerService服務之外，還啟動了其它很多的服務，例如在前面學習Activity和Service的幾篇文章中經常看到的ActivityManagerService服務，有興趣的讀者可以自己研究一下。 **Step 7. PackageManagerService.main** 這個函數定義在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; } ...... } ~~~ 這個函數創建了一個PackageManagerService服務實例，然后把這個服務添加到ServiceManager中去，ServiceManager是Android系統Binder進程間通信機制的守護進程，負責管理系統中的Binder對象，具體可以參考淺談Service Manager成為Android進程間通信（IPC）機制Binder守護進程之路一文。在創建這個PackageManagerService服務實例時，會在PackageManagerService類的構造函數中開始執行安裝應用程序的過程： ~~~ 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); ...... } } } ...... } ~~~ 這里會調用scanDirLI函數來掃描移動設備上的下面這五個目錄中的Apk文件： * /system/framework * /system/app * /vendor/app * /data/app * /data/app-private **Step 8. PackageManagerService.scanDirLI** 這個函數定義在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's continue; } 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 apk Slog.w(TAG, "Cleaning up failed install of " + file); file.delete(); } } } ...... } ~~~ 對于目錄中的每一個文件，如果是以后Apk作為后綴名，那么就調用scanPackageLI函數來對它進行解析和安裝。 **Step 9. PackageManagerService.scanPackageLI** 這個函數定義在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); } ...... } ~~~ 這個函數首先會為這個Apk文件創建一個PackageParser實例，接著調用這個實例的parsePackage函數來對這個Apk文件進行解析。這個函數最后還會調用另外一個版本的scanPackageLI函數把來解析后得到的應用程序信息保存在PackageManagerService中。 **Step 10. PackageParser.parsePackage** 這個函數定義在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 paths pkg.mPath = destCodePath; pkg.mScanPath = mArchiveSourcePath; //pkg.applicationInfo.sourceDir = destCodePath; //pkg.applicationInfo.publicSourceDir = destRes; pkg.mSignatures = null; return pkg; } ...... } ~~~ 每一個Apk文件都是一個歸檔文件，它里面包含了Android應用程序的配置文件AndroidManifest.xml，這里主要就是要對這個配置文件就行解析了，從Apk歸檔文件中得到這個配置文件后，就調用另一外版本的parsePackage函數對這個應用程序進行解析了： ~~~ 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; } ...... } ~~~ 這里就是對AndroidManifest.xml文件中的各個標簽進行解析了，各個標簽的含義可以參考官方文檔http://developer.android.com/guide/topics/manifest/manifest-intro.html，這里我們只簡單看一下application標簽的解析，這是通過調用parseApplication函數來進行的。 **Step 11. PackageParser.parseApplication** 這個函數定義在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; } ...... } ~~~ 這里就是對AndroidManifest.xml文件中的application標簽進行解析了，我們常用到的標簽就有activity、service、receiver和provider，各個標簽的含義可以參考官方文檔http://developer.android.com/guide/topics/manifest/manifest-intro.html。這里解析完成后，一層層返回到Step 9中，調用另一個版本的scanPackageLI函數把來解析后得到的應用程序信息保存下來。 **Step 12. PackageManagerService.scanPackageLI** 這個函數定義在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 mPackages mPackages.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; } ...... } ~~~ 這個函數主要就是把前面解析應用程序得到的package、provider、service、receiver和activity等信息保存在PackageManagerService服務中了。這樣，在Android系統啟動的時候安裝應用程序的過程就介紹完了，但是，這些應用程序只是相當于在PackageManagerService服務注冊好了，如果我們想要在Android桌面上看到這些應用程序，還需要有一個Home應用程序，負責從PackageManagerService服務中把這些安裝好的應用程序取出來，并以友好的方式在桌面上展現出來，例如以快捷圖標的形式。在Android系統中，負責把系統中已經安裝的應用程序在桌面中展現出來的Home應用程序就是Launcher了，在下一篇文章中，我們將介紹Launcher是如何啟動的以及它是如何從PackageManagerService服務中把系統中已經安裝好的應用程序展現出來的，敬請期待。