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目录

Android应用启动之从Launcher拉起APP(一)Android应用启动之从Launcher拉起APP(二)Android应用启动之从Launcher拉起APP(三)Android应用启动之从Launcher拉起APP时序图

上文中写到，写到从AMS->ZygoteServer->ActivityThread。继续承接上文。

ActivityThread启动主线程

进入android.app.activethread类后，开始执行main函数：

public static void main(String[] args) {Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");SamplingProfilerIntegration.start();CloseGuard.setEnabled(false);Environment.initForCurrentUser();EventLogger.setReporter(new EventLoggingReporter());final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());TrustedCertificateStore.setDefaultUserDirectory(configDir);Process.setArgV0("<pre-initialized>");Looper.prepareMainLooper();ActivityThread thread = new ActivityThread();thread.attach(false);if (sMainThreadHandler == null) {sMainThreadHandler = thread.getHandler();}if (false) {Looper.myLooper().setMessageLogging(newLogPrinter(Log.DEBUG, "ActivityThread"));}Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);Looper.loop();throw new RuntimeException("Main thread loop unexpectedly exited");}

函数中会创建消息处理，并执行了ActivityThread的attach函数：

private void attach(boolean system) {sCurrentActivityThread = this;mSystemThread = system;if (!system) {ViewRootImpl.addFirstDrawHandler(new Runnable() {@Overridepublic void run() {ensureJitEnabled();}});android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",UserHandle.myUserId());RuntimeInit.setApplicationObject(mAppThread.asBinder());final IActivityManager mgr = ActivityManager.getService();try {// 执行ActivityManagerServer的attachApplication函数mgr.attachApplication(mAppThread);} catch (RemoteException ex) {throw ex.rethrowFromSystemServer();}……}

ActivityThread通过Binder将ApplicationThread对象传递给ActivityManagerService。
ActivityManagerService的attachApplication函数：

public final void attachApplication(IApplicationThread thread) {synchronized (this) {int callingPid = Binder.getCallingPid();final long origId = Binder.clearCallingIdentity();attachApplicationLocked(thread, callingPid);Binder.restoreCallingIdentity(origId);}

进入到attachApplicationLocked函数：

private final boolean attachApplicationLocked(IApplicationThread thread,int pid) {ProcessRecord app;long startTime = SystemClock.uptimeMillis();if (pid != MY_PID && pid >= 0) {synchronized (mPidsSelfLocked) {app = mPidsSelfLocked.get(pid);}} else {app = null;}if (app == null) {……}// 清除ProcessRecord中的信息，以确保没有不相关进程的信息if (app.thread != null) {handleAppDiedLocked(app, true, true);}if (DEBUG_ALL) Slog.v(TAG, "Binding process pid " + pid + " to record " + app);final String processName = app.processName;try {// 注册AppDeathRecipient，保证意外关闭时候系统能收到信息AppDeathRecipient adr = new AppDeathRecipient(app, pid, thread);thread.asBinder().linkToDeath(adr, 0);app.deathRecipient = adr;} catch (RemoteException e) {……}EventLog.writeEvent(EventLogTags.AM_PROC_BOUND, app.userId, app.pid, app.processName);app.makeActive(thread, mProcessStats);app.curAdj = app.setAdj = app.verifiedAdj = ProcessList.INVALID_ADJ;app.curSchedGroup = app.setSchedGroup = ProcessList.SCHED_GROUP_DEFAULT;app.forcingToImportant = null;updateProcessForegroundLocked(app, false, false);app.hasShownUi = false;app.debugging = false;app.cached = false;app.killedByAm = false;app.killed = false;……// 调用ActivityThread的bindApplication方法checkTime(startTime, "attachApplicationLocked: immediately before bindApplication");mStackSupervisor.mActivityMetricsLogger.notifyBindApplication(app);if (app.instr != null) {thread.bindApplication(processName, appInfo, providers,app.instr.mClass,profilerInfo, app.instr.mArguments,app.instr.mWatcher,app.instr.mUiAutomationConnection, testMode,mBinderTransactionTrackingEnabled, enableTrackAllocation,isRestrictedBackupMode || !normalMode, app.persistent,new Configuration(getGlobalConfiguration()), app.compat,getCommonServicesLocked(app.isolated),mCoreSettingsObserver.getCoreSettingsLocked(),buildSerial);} else {thread.bindApplication(processName, appInfo, providers, null, profilerInfo,null, null, null, testMode,mBinderTransactionTrackingEnabled, enableTrackAllocation,isRestrictedBackupMode || !normalMode, app.persistent,new Configuration(getGlobalConfiguration()), app.compat,getCommonServicesLocked(app.isolated),mCoreSettingsObserver.getCoreSettingsLocked(),buildSerial);}checkTime(startTime, "attachApplicationLocked: immediately after bindApplication");updateLruProcessLocked(app, false, null);checkTime(startTime, "attachApplicationLocked: after updateLruProcessLocked");app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();} catch (Exception e) {……}mPersistentStartingProcesses.remove(app);if (DEBUG_PROCESSES && mProcessesOnHold.contains(app)) Slog.v(TAG_PROCESSES,"Attach application locked removing on hold: " + app);mProcessesOnHold.remove(app);boolean badApp = false;boolean didSomething = false;// 执行ActivityStack中的attachApplicationLocked函数if (normalMode) {try {if (mStackSupervisor.attachApplicationLocked(app)) {didSomething = true;}} catch (Exception e) {Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);badApp = true;}}……return true;}

从上文代码知道，ActivityManagerService有执行了ActivityThread的bindApplication函数：

public final void bindApplication(String processName, ApplicationInfo appInfo,List<ProviderInfo> providers, ComponentName instrumentationName,ProfilerInfo profilerInfo, Bundle instrumentationArgs,IInstrumentationWatcher instrumentationWatcher,IUiAutomationConnection instrumentationUiConnection, int debugMode,boolean enableBinderTracking, boolean trackAllocation,boolean isRestrictedBackupMode, boolean persistent, Configuration config,CompatibilityInfo compatInfo, Map services, Bundle coreSettings,String buildSerial) {if (services != null) {ServiceManager.initServiceCache(services);}setCoreSettings(coreSettings);AppBindData data = new AppBindData();data.processName = processName;data.appInfo = appInfo;data.providers = providers;data.instrumentationName = instrumentationName;data.instrumentationArgs = instrumentationArgs;data.instrumentationWatcher = instrumentationWatcher;data.instrumentationUiAutomationConnection = instrumentationUiConnection;data.debugMode = debugMode;data.enableBinderTracking = enableBinderTracking;data.trackAllocation = trackAllocation;data.restrictedBackupMode = isRestrictedBackupMode;data.persistent = persistent;data.config = config;data.compatInfo = compatInfo;data.initProfilerInfo = profilerInfo;data.buildSerial = buildSerial;sendMessage(H.BIND_APPLICATION, data);}

bindApplicationhan函数中会像消息处理发送BIND_APPLICATION消息：

case BIND_APPLICATION:Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");AppBindData data = (AppBindData)msg.obj;handleBindApplication(data);Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);break;

最后会执行handleBindApplication函数：

private void handleBindApplication(AppBindData data) {// 设置虚拟机信息VMRuntime.registerSensitiveThread();if (data.trackAllocation) {DdmVmInternal.enableRecentAllocations(true);}……Process.setArgV0(data.processName);android.ddm.DdmHandleAppName.setAppName(data.processName,UserHandle.myUserId());//设置进程运行信息……final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);updateLocaleListFromAppContext(appContext,mResourcesManager.getConfiguration().getLocales());……
.final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskWrites();try {Application app = data.info.makeApplication(data.restrictedBackupMode, null);mInitialApplication = app;if (!data.restrictedBackupMode) {if (!ArrayUtils.isEmpty(data.providers)) {installContentProviders(app, data.providers);mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);}}try {mInstrumentation.onCreate(data.instrumentationArgs);}catch (Exception e) {……}try {mInstrumentation.callApplicationOnCreate(app);} catch (Exception e) {……}} finally {StrictMode.setThreadPolicy(savedPolicy);}// 加载字体资源FontsContract.setApplicationContextForResources(appContext);try {final ApplicationInfo info =getPackageManager().getApplicationInfo(data.appInfo.packageName,PackageManager.GET_META_DATA /*flags*/,UserHandle.myUserId());if (info.metaData != null) {final int preloadedFontsResource = info.metaData.getInt(ApplicationInfo.METADATA_PRELOADED_FONTS, 0);if (preloadedFontsResource != 0) {data.info.mResources.preloadFonts(preloadedFontsResource);}}} catch (RemoteException e) {throw e.rethrowFromSystemServer();}}

ActivityManagerServiceh中后续执行了ActivityStackSupervisor类的attachApplicationLocked函数：

boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {final String processName = app.processName;boolean didSomething = false;for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {final ActivityStack stack = stacks.get(stackNdx);if (!isFocusedStack(stack)) {continue;}// 获取Activity的描述ActivityRecord hr = stack.topRunningActivityLocked();if (hr != null) {if (hr.app == null && app.uid == hr.info.applicationInfo.uid&& processName.equals(hr.processName)) {try {// 执行启动Activityif (realStartActivityLocked(hr, app, true, true)) {didSomething = true;}} catch (RemoteException e) {Slog.w(TAG, "Exception in new application when starting activity "+ hr.intent.getComponent().flattenToShortString(), e);throw e;}}}}}if (!didSomething) {// 继续执行显示ActivityensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);}return didSomething;}

到这里，后面就该ActivityThread调度执行Activity生命周期方法，完成Activity的启动。realStartActivityLocked函数：

final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,boolean andResume, boolean checkConfig) throws RemoteException {……app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,System.identityHashCode(r), r.info,// TODO: Have this take the merged configuration instead of separate global and// override configs.mergedConfiguration.getGlobalConfiguration(),mergedConfiguration.getOverrideConfiguration(), r.compat,r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,r.persistentState, results, newIntents, !andResume,mService.isNextTransitionForward(), profilerInfo)……return true;}

最后又执行回去ActivityThread的scheduleLaunchActivity函数：

public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,ActivityInfo info, Configuration curConfig, Configuration overrideConfig,CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,int procState, Bundle state, PersistableBundle persistentState,List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) {updateProcessState(procState, false);ActivityClientRecord r = new ActivityClientRecord();r.token = token;r.ident = ident;r.intent = intent;r.referrer = referrer;r.voiceInteractor = voiceInteractor;r.activityInfo = info;r.compatInfo = compatInfo;r.state = state;r.persistentState = persistentState;r.pendingResults = pendingResults;r.pendingIntents = pendingNewIntents;r.startsNotResumed = notResumed;r.isForward = isForward;r.profilerInfo = profilerInfo;r.overrideConfig = overrideConfig;updatePendingConfiguration(curConfig);sendMessage(H.LAUNCH_ACTIVITY, r);}case LAUNCH_ACTIVITY: {Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");final ActivityClientRecord r = (ActivityClientRecord) msg.obj;r.packageInfo = getPackageInfoNoCheck(r.activityInfo.applicationInfo, r.compatInfo);handleLaunchActivity(r, null, "LAUNCH_ACTIVITY");Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);} break;

接续跟踪，执行到了handleLaunchActivity函数：

private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {……Activity a = performLaunchActivity(r, customIntent);if (a != null) {r.createdConfig = new Configuration(mConfiguration);reportSizeConfigurations(r);Bundle oldState = r.state;handleResumeActivity(r.token, false, r.isForward,!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);if (!r.activity.mFinished && r.startsNotResumed) {performPauseActivityIfNeeded(r, reason);if (r.isPreHoneycomb()) {r.state = oldState;}}} else {……}}

进入performLaunchActivity函数(从函数名字就知道他是用来处理启动Activity的)：

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {ActivityInfo aInfo = r.activityInfo;if (r.packageInfo == null) {r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,Context.CONTEXT_INCLUDE_CODE);}ComponentName component = r.intent.getComponent();if (component == null) {component = r.intent.resolveActivity(mInitialApplication.getPackageManager());r.intent.setComponent(component);}if (r.activityInfo.targetActivity != null) {component = new ComponentName(r.activityInfo.packageName,r.activityInfo.targetActivity);}ContextImpl appContext = createBaseContextForActivity(r);Activity activity = null;try {java.lang.ClassLoader cl = appContext.getClassLoader();// 根据类名字，创建activity对象activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);StrictMode.incrementExpectedActivityCount(activity.getClass());r.intent.setExtrasClassLoader(cl);r.intent.prepareToEnterProcess();if (r.state != null) {r.state.setClassLoader(cl);}} catch (Exception e) {if (!mInstrumentation.onException(activity, e)) {throw new RuntimeException("Unable to instantiate activity " + component+ ": " + e.toString(), e);}}try {Application app = r.packageInfo.makeApplication(false, mInstrumentation);if (localLOGV) Slog.v(TAG, "Performing launch of " + r);if (localLOGV) Slog.v(TAG, r + ": app=" + app+ ", appName=" + app.getPackageName()+ ", pkg=" + r.packageInfo.getPackageName()+ ", comp=" + r.intent.getComponent().toShortString()+ ", dir=" + r.packageInfo.getAppDir());if (activity != null) {CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());Configuration config = new Configuration(mCompatConfiguration);if (r.overrideConfig != null) {config.updateFrom(r.overrideConfig);}if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "+ r.activityInfo.name + " with config " + config);Window window = null;if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {window = r.mPendingRemoveWindow;r.mPendingRemoveWindow = null;r.mPendingRemoveWindowManager = null;}appContext.setOuterContext(activity);// 执行activity的attach函数activity.attach(appContext, this, getInstrumentation(), r.token,r.ident, app, r.intent, r.activityInfo, title, r.parent,r.embeddedID, r.lastNonConfigurationInstances, config,r.referrer, r.voiceInteractor, window, r.configCallback);if (customIntent != null) {activity.mIntent = customIntent;}r.lastNonConfigurationInstances = null;checkAndBlockForNetworkAccess();activity.mStartedActivity = false;int theme = r.activityInfo.getThemeResource();if (theme != 0) {activity.setTheme(theme);}activity.mCalled = false;// 执行activity的OnCreat函数if (r.isPersistable()) {mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);} else {mInstrumentation.callActivityOnCreate(activity, r.state);}if (!activity.mCalled) {throw new SuperNotCalledException("Activity " + r.intent.getComponent().toShortString() +" did not call through to super.onCreate()");}r.activity = activity;r.stopped = true;if (!r.activity.mFinished) {// 执行activity的onStart函数activity.performStart();r.stopped = false;}if (!r.activity.mFinished) {if (r.isPersistable()) {if (r.state != null || r.persistentState != null) {mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,r.persistentState);}} else if (r.state != null) {mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);}}if (!r.activity.mFinished) {activity.mCalled = false;if (r.isPersistable()) {mInstrumentation.callActivityOnPostCreate(activity, r.state,r.persistentState);} else {mInstrumentation.callActivityOnPostCreate(activity, r.state);}if (!activity.mCalled) {throw new SuperNotCalledException("Activity " + r.intent.getComponent().toShortString() +" did not call through to super.onPostCreate()");}}}r.paused = true;mActivities.put(r.token, r);} catch (SuperNotCalledException e) {throw e;} catch (Exception e) {if (!mInstrumentation.onException(activity, e)) {throw new RuntimeException("Unable to start activity " + component+ ": " + e.toString(), e);}}return activity;}

这样就开始Activity的生命周期。

最后看一下handleLaunchActivity中调用的handleResumeActivity函数：

final void handleResumeActivity(IBinder token,boolean clearHide, boolean isForward, boolean reallyResume) {// If we are getting ready to gc after going to the background, well// we are back active so skip it.unscheduleGcIdler();mSomeActivitiesChanged = true;// TODO Push resumeArgs into the activity for considerationActivityClientRecord r = performResumeActivity(token, clearHide);……
}

这样子就app启动完成了。

总结

APP启动大致需要六步骤：
(1)Launcher响应了用户的点击事件，然后通知AMS；
(2)AMS得到Launcher的通知，新建一个Task去准备启动Activity，并且Paused Launcher；
(3)Launcher得到AMS消息，那么就直接挂起，并告诉AMS已经Paused了；
(4)AMS知道了Launcher已经挂起之后，为新的Activity准备启动工作，AMS通过Socket去和Zygote通信，创建进程，然后创建一个线程，新的进程会导入ActivityThread类，这就是每一个应用程序都有一个ActivityThread与之对应的原因；
(5)进程创建好了，通过调用上述的ActivityThread的main方法，这是应用程序的入口，在这里开启消息循环队列，这也是主线程默认绑定Looper的原因；
(6)这时候，App还没有启动完，要永远记住，四大组建的启动都需要AMS去启动，将上述的应用进程信息注册到AMS中，AMS再在堆栈顶部取得要启动的Activity，通过一系列链式调用去完成App启动；

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