Android应用框架之PackageManagerService _Android应用

冲天香阵透长安，满城尽带黄金甲。这篇文章主要讲述Android应用框架之PackageManagerService相关的知识，希望能为你提供帮助。
系统在启动的时候会启动一个叫做PackageManagerService的服务，顾名思义，这个服务主要管理安装在设备上的应用程序，其中最为重要的工作就是在在系统启动之后，PackageManagerService会扫描特定目录下地以apk为后缀的文件，然后将对应的应用安装到系统中。注意，这里的安装并不是我们平时所说的安装，它指的的是将存放在磁盘之上的静态应用程序文件进行解析，并将相关信息注册到系统中。而具体的解析工作实际就是读取应用的配置文件manifest.xml，并将文件中配置的组件
（Activity,Service,BroadcastRecevier,ContentProvider），权限等信息注册到PackageManagerService中。
本篇博客主要介绍PackageManagerService的启动过程，以及PackageManagerService如何安装各个应用程序。
1.PackageManagerService启动过程
和ActivityManagerService，WindowManagerService一样，PackageManagerService是一个系统级的服务，运行在独立的进程中，而所有的系统级服务都是由SystemServer启动的。所以首先来看看SystemServer的启动过程。
1) SystemServer启动：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。

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

2)SystemServer.system_init经过一系列调用后转到system_init方法，这是一个JNI方法

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; }

在这个方法中，创建了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。init2函数很简单，创建一个线程，而PackageManagerService就是在这个线程中创建的。

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(); } }

3)ServerThread.run

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

在这个线程中创建了PackageManagerService,并同时启动了其main函数。另外在这个线程中还启动了ActivityManagerService等其他Service
2.应用安装
【Android应用框架之PackageManagerService】接下来再来看看PackageManagerService启动之后如何进行应用程序的安装。
1）PackageManagerService.main

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; } ...... }

可以看到，创建完成后，就加载到ServiceManager中。接下来看看PackageManagerService的构造函数：

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

可以看到，在构造函数中，PackageManagerService(PMS)会扫描特定目录下的APK文件，然后进行相关的加载工作，这些目录包括：

/system/framework
/system/app
/vendor/app
/data/app
/data/app-private

在每个路径下，都调用了scanDirLI函数，接下来看看对应的函数做了些什么。
2）PackageParser.parsePackagescanDirLI中又经过多次调用，具体就是扫描对应目录的文件，如果是apk文件，就找到apk文件中的manifest文件，最后再为每一个apk创建一个PackageParser对象，并将manifest文件传递给PackageParser.parsePackage。

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; }...... 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application标签进行解析了，我们常用到的标签就有activity、service、receiver和provider，这里解析完成后，一层层返回，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。

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; }...... }

到这里整个应用的安装过程就介绍完了。其实整个过程还是很明确，清晰的。
接下来再来总结一下整个启动过程：