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：

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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：

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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：

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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：

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/*

* 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：

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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：

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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：

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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：

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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：

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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：

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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：

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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：

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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：

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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：

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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。

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