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。