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 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;
}

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 {
	......

	@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);
		}

		......
	}

	......
}

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'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();
			}
		}
	}


	......
}

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 paths
		pkg.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 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;
	}

	......
}

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。