前言

由于工作原因需要了解activity启动流程，在网上已经有很多相关文章，不过为了记忆深刻还是自己无脑跑一遍流程，接下来是Android 10 Q Android api 29 的无脑跟流程。

这次流程跟踪是activity冷启动，也就是相当于一个A端APP通过intent启动另外一个B端APP的首次启动流程。

无脑跟开始：

第一阶段：activity.startActivity --》 ActivityTaskManagerService (ATMS)

启动入口：

Activity.java

    public void startActivity(Intent intent) {this.startActivity(intent, null);}

到:

    @Overridepublic void startActivity(Intent intent, @Nullable Bundle options) {if (options != null) {startActivityForResult(intent, -1, options);} else {// Note we want to go through this call for compatibility with// applications that may have overridden the method.startActivityForResult(intent, -1);}}

option == null 所以调用startActivityForResult(intent, -1);

    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode) {startActivityForResult(intent, requestCode, null);}

到：

    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,@Nullable Bundle options) {if (mParent == null) {options = transferSpringboardActivityOptions(options);Instrumentation.ActivityResult ar =mInstrumentation.execStartActivity(this, mMainThread.getApplicationThread(), mToken, this,intent, requestCode, options);if (ar != null) {mMainThread.sendActivityResult(mToken, mEmbeddedID, requestCode, ar.getResultCode(),ar.getResultData());}if (requestCode >= 0) {// If this start is requesting a result, we can avoid making// the activity visible until the result is received.  Setting// this code during onCreate(Bundle savedInstanceState) or onResume() will keep the// activity hidden during this time, to avoid flickering.// This can only be done when a result is requested because// that guarantees we will get information back when the// activity is finished, no matter what happens to it.mStartedActivity = true;}cancelInputsAndStartExitTransition(options);// TODO Consider clearing/flushing other event sources and events for child windows.} else {if (options != null) {mParent.startActivityFromChild(this, intent, requestCode, options);} else {// Note we want to go through this method for compatibility with// existing applications that may have overridden it.mParent.startActivityFromChild(this, intent, requestCode);}}}

这里会调用mInstrumentation.execStartActivity； Instrumentation又是仪表盘类，所有的生命周期的控制都在里面调用例如：onCreate、onStrart等。

Instrumentation.java

    public ActivityResult execStartActivity(Context who, IBinder contextThread, IBinder token, Activity target,Intent intent, int requestCode, Bundle options) {IApplicationThread whoThread = (IApplicationThread) contextThread;Uri referrer = target != null ? target.onProvideReferrer() : null;if (referrer != null) {intent.putExtra(Intent.EXTRA_REFERRER, referrer);}if (mActivityMonitors != null) {synchronized (mSync) {final int N = mActivityMonitors.size();for (int i=0; ifinal ActivityMonitor am = mActivityMonitors.get(i);ActivityResult result = null;if (am.ignoreMatchingSpecificIntents()) {result = am.onStartActivity(intent);}if (result != null) {am.mHits++;return result;} else if (am.match(who, null, intent)) {am.mHits++;if (am.isBlocking()) {return requestCode >= 0 ? am.getResult() : null;}break;}}}}try {intent.migrateExtraStreamToClipData();intent.prepareToLeaveProcess(who);int result = ActivityTaskManager.getService().startActivity(whoThread, who.getBasePackageName(), intent,intent.resolveTypeIfNeeded(who.getContentResolver()),token, target != null ? target.mEmbeddedID : null,requestCode, 0, null, options);checkStartActivityResult(result, intent);} catch (RemoteException e) {throw new RuntimeException("Failure from system", e);}return null;}

在Android 10以后也就是Q版本以后管理activity启动这块的服务从ActivityManagerService变成了ActivityTaskManagerService；ActivityTaskManager.getService()就是获取ActivityTaskManagerService跨进程调用binder代理对象。
我们可以跟踪ActivityTaskManager.getService，

    public static IActivityTaskManager getService() {return IActivityTaskManagerSingleton.get();}

到：

    private static final Singleton IActivityTaskManagerSingleton =new Singleton() {@Overrideprotected IActivityTaskManager create() {final IBinder b = ServiceManager.getService(Context.ACTIVITY_TASK_SERVICE);return IActivityTaskManager.Stub.asInterface(b);}};

这里获取了一个单例对象IActivityTaskManager 就是ActivityTaskManagerService的binder调用端代理（如果不了解binder机制需要先了解binder机制,源码中大量使用binder通讯）。最终获取调用ActivityTaskManagerService的startActivity方法。

第二阶段:ATMS 启动activity流程到是否要执行冷启动，创建APP进程。

ActivityTaskManagerService.java

    public final int startActivity(IApplicationThread caller, String callingPackage,Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,resultWho, requestCode, startFlags, profilerInfo, bOptions,UserHandle.getCallingUserId());}

我们来看看ATMS收到APP的参数是哪些：
caller: A端APP的ApplicationThread
callingPackage: A端APP的activity的包名
intent: A端APP启动B端APP的意图
resolvedType: intent.resolveTypeIfNeeded
resultTo: A端APP在AMS中ActivityRecord
resultWho: 来自于当前Activity.mEmbeddedID
requestCode：请求码

    @Overridepublic int startActivityAsUser(IApplicationThread caller, String callingPackage,Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) {return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,true /*validateIncomingUser*/);}

到：

    @Overridepublic int startActivityAsUser(IApplicationThread caller, String callingPackage,Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) {return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,resultWho, requestCode, startFlags, profilerInfo, bOptions, userId,true /*validateIncomingUser*/);}

到：

    int startActivityAsUser(IApplicationThread caller, String callingPackage,Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId,boolean validateIncomingUser) {enforceNotIsolatedCaller("startActivityAsUser");userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");// TODO: Switch to user app stacks here.return getActivityStartController().obtainStarter(intent, "startActivityAsUser").setCaller(caller).setCallingPackage(callingPackage).setResolvedType(resolvedType).setResultTo(resultTo).setResultWho(resultWho).setRequestCode(requestCode).setStartFlags(startFlags).setProfilerInfo(profilerInfo).setActivityOptions(bOptions).setMayWait(userId).execute();}

getActivityStartController().obtainStarter获取ActivityStarter类，然后调用execute方法：

ActivityStarter.java

    int execute() {try {// TODO(b/64750076): Look into passing request directly to these methods to allow// for transactional diffs and preprocessing.if (mRequest.mayWait) {return startActivityMayWait(mRequest.caller, mRequest.callingUid,mRequest.callingPackage, mRequest.realCallingPid, mRequest.realCallingUid,mRequest.intent, mRequest.resolvedType,mRequest.voiceSession, mRequest.voiceInteractor, mRequest.resultTo,mRequest.resultWho, mRequest.requestCode, mRequest.startFlags,mRequest.profilerInfo, mRequest.waitResult, mRequest.globalConfig,mRequest.activityOptions, mRequest.ignoreTargetSecurity, mRequest.userId,mRequest.inTask, mRequest.reason,mRequest.allowPendingRemoteAnimationRegistryLookup,mRequest.originatingPendingIntent, mRequest.allowBackgroundActivityStart);} else {.............}} finally {onExecutionComplete();}}

到：

    private int startActivityMayWait(IApplicationThread caller, int callingUid,String callingPackage, int requestRealCallingPid, int requestRealCallingUid,Intent intent, String resolvedType, IVoiceInteractionSession voiceSession,IVoiceInteractor voiceInteractor, IBinder resultTo, String resultWho, int requestCode,int startFlags, ProfilerInfo profilerInfo, WaitResult outResult,Configuration globalConfig, SafeActivityOptions options, boolean ignoreTargetSecurity,int userId, TaskRecord inTask, String reason,boolean allowPendingRemoteAnimationRegistryLookup,PendingIntentRecord originatingPendingIntent, boolean allowBackgroundActivityStart) {......................final ActivityRecord[] outRecord = new ActivityRecord[1];int res = startActivity(caller, intent, ephemeralIntent, resolvedType, aInfo, rInfo,voiceSession, voiceInteractor, resultTo, resultWho, requestCode, callingPid,callingUid, callingPackage, realCallingPid, realCallingUid, startFlags, options,ignoreTargetSecurity, componentSpecified, outRecord, inTask, reason,allowPendingRemoteAnimationRegistryLookup, originatingPendingIntent,allowBackgroundActivityStart);Binder.restoreCallingIdentity(origId);......................}

到：

    private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,String callingPackage, int realCallingPid, int realCallingUid, int startFlags,SafeActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,ActivityRecord[] outActivity, TaskRecord inTask, String reason,boolean allowPendingRemoteAnimationRegistryLookup,PendingIntentRecord originatingPendingIntent, boolean allowBackgroundActivityStart) {...........................mLastStartActivityResult = startActivity(caller, intent, ephemeralIntent, resolvedType,aInfo, rInfo, voiceSession, voiceInteractor, resultTo, resultWho, requestCode,callingPid, callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,options, ignoreTargetSecurity, componentSpecified, mLastStartActivityRecord,inTask, allowPendingRemoteAnimationRegistryLookup, originatingPendingIntent,allowBackgroundActivityStart);...............................return getExternalResult(mLastStartActivityResult);}

到：

    private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,String callingPackage, int realCallingPid, int realCallingUid, int startFlags,SafeActivityOptions options,boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity,TaskRecord inTask, boolean allowPendingRemoteAnimationRegistryLookup,PendingIntentRecord originatingPendingIntent, boolean allowBackgroundActivityStart) {.......................................mService.onStartActivitySetDidAppSwitch();mController.doPendingActivityLaunches(false);final int res = startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags,true /* doResume */, checkedOptions, inTask, outActivity, restrictedBgActivity);mSupervisor.getActivityMetricsLogger().notifyActivityLaunched(res, outActivity[0]);return res;}

到：

private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,ActivityRecord[] outActivity, boolean restrictedBgActivity) {int result = START_CANCELED;final ActivityStack startedActivityStack;try {mService.mWindowManager.deferSurfaceLayout();result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor,startFlags, doResume, options, inTask, outActivity, restrictedBgActivity);}..........................
}

到：

    // Note: This method should only be called from {@link startActivity}.private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,ActivityRecord[] outActivity, boolean restrictedBgActivity) {..............................// If the target stack was not previously focusable (previous top running activity// on that stack was not visible) then any prior calls to move the stack to the// will not update the focused stack.  If starting the new activity now allows the// task stack to be focusable, then ensure that we now update the focused stack// accordingly.if (mTargetStack.isFocusable()&& !mRootActivityContainer.isTopDisplayFocusedStack(mTargetStack)) {mTargetStack.moveToFront("startActivityUnchecked");}mRootActivityContainer.resumeFocusedStacksTopActivities(mTargetStack, mStartActivity, mOptions);..............................}

RootActivityContainer.java

 boolean resumeFocusedStacksTopActivities(ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {if (!mStackSupervisor.readyToResume()) {return false;}boolean result = false;if (targetStack != null && (targetStack.isTopStackOnDisplay()|| getTopDisplayFocusedStack() == targetStack)) {result = targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);}......................return result;}

ActivityStack.java

    boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {if (mInResumeTopActivity) {// Don't even start recursing.return false;}boolean result = false;try {// Protect against recursion.mInResumeTopActivity = true;result = resumeTopActivityInnerLocked(prev, options);// When resuming the top activity, it may be necessary to pause the top activity (for// example, returning to the lock screen. We suppress the normal pause logic in// {@link #resumeTopActivityUncheckedLocked}, since the top activity is resumed at the// end. We call the {@link ActivityStackSupervisor#checkReadyForSleepLocked} again here// to ensure any necessary pause logic occurs. In the case where the Activity will be// shown regardless of the lock screen, the call to// {@link ActivityStackSupervisor#checkReadyForSleepLocked} is skipped.final ActivityRecord next = topRunningActivityLocked(true /* focusableOnly */);if (next == null || !next.canTurnScreenOn()) {checkReadyForSleep();}} finally {mInResumeTopActivity = false;}return result;}

到：

    private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {...........................// Whoops, need to restart this activity!if (!next.hasBeenLaunched) {next.hasBeenLaunched = true;} else {if (SHOW_APP_STARTING_PREVIEW) {next.showStartingWindow(null /* prev */, false /* newTask */,false /* taskSwich */);}if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Restarting: " + next);}if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Restarting " + next);mStackSupervisor.startSpecificActivityLocked(next, true, true);............................}

ActivityStackSupervisor.java

    void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {// Is this activity's application already running?final WindowProcessController wpc =mService.getProcessController(r.processName, r.info.applicationInfo.uid);boolean knownToBeDead = false;if (wpc != null && wpc.hasThread()) {try {realStartActivityLocked(r, wpc, andResume, checkConfig);return;} catch (RemoteException e) {Slog.w(TAG, "Exception when starting activity "+ r.intent.getComponent().flattenToShortString(), e);}// If a dead object exception was thrown -- fall through to// restart the application.knownToBeDead = true;}// Suppress transition until the new activity becomes ready, otherwise the keyguard can// appear for a short amount of time before the new process with the new activity had the// ability to set its showWhenLocked flags.if (getKeyguardController().isKeyguardLocked()) {r.notifyUnknownVisibilityLaunched();}try {if (Trace.isTagEnabled(TRACE_TAG_ACTIVITY_MANAGER)) {Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "dispatchingStartProcess:"+ r.processName);}// Post message to start process to avoid possible deadlock of calling into AMS with the// ATMS lock held.final Message msg = PooledLambda.obtainMessage(ActivityManagerInternal::startProcess, mService.mAmInternal, r.processName,r.info.applicationInfo, knownToBeDead, "activity", r.intent.getComponent());mService.mH.sendMessage(msg);} finally {Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);}}

这里是判断冷启动地方，if (wpc != null && wpc.hasThread())条件判断要启动APP是否对应进程已经启动了，如果启动执行realStartActivityLocked(r, wpc, andResume, checkConfig)进入热启动；如果进程没有启动则进入启动进程流程，会给mService.mH发送一个消息，这个消息会通过进程通讯传递给ATMS并且调用startProcessLocked方法：

ActivityManagerService.java

    final ProcessRecord startProcessLocked(String processName,ApplicationInfo info, boolean knownToBeDead, int intentFlags,HostingRecord hostingRecord, boolean allowWhileBooting,boolean isolated, boolean keepIfLarge) {return mProcessList.startProcessLocked(processName, info, knownToBeDead, intentFlags,hostingRecord, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,null /* crashHandler */);}

ProcessList.java

    final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,boolean knownToBeDead, int intentFlags, HostingRecord hostingRecord,boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {...............................checkSlow(startTime, "startProcess: stepping in to startProcess");final boolean success = startProcessLocked(app, hostingRecord, abiOverride);checkSlow(startTime, "startProcess: done starting proc!");return success ? app : null;}

到：

    final boolean startProcessLocked(ProcessRecord app, HostingRecord hostingRecord,String abiOverride) {return startProcessLocked(app, hostingRecord,false /* disableHiddenApiChecks */, false /* mountExtStorageFull */, abiOverride);}

到：

    boolean startProcessLocked(ProcessRecord app, HostingRecord hostingRecord,boolean disableHiddenApiChecks, boolean mountExtStorageFull,String abiOverride) {..............................................final String seInfo = app.info.seInfo+ (TextUtils.isEmpty(app.info.seInfoUser) ? "" : app.info.seInfoUser);// Start the process.  It will either succeed and return a result containing// the PID of the new process, or else throw a RuntimeException.final String entryPoint = "android.app.ActivityThread";return startProcessLocked(hostingRecord, entryPoint, app, uid, gids,runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet, invokeWith,startTime);..............................................}

到：

    boolean startProcessLocked(HostingRecord hostingRecord,String entryPoint,ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,String seInfo, String requiredAbi, String instructionSet, String invokeWith,long startTime) {....................................try {final Process.ProcessStartResult startResult = startProcess(hostingRecord,entryPoint, app,uid, gids, runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet,invokeWith, startTime);handleProcessStartedLocked(app, startResult.pid, startResult.usingWrapper,startSeq, false);} catch (RuntimeException e) {Slog.e(ActivityManagerService.TAG, "Failure starting process "+ app.processName, e);app.pendingStart = false;mService.forceStopPackageLocked(app.info.packageName, UserHandle.getAppId(app.uid),false, false, true, false, false, app.userId, "start failure");}return app.pid > 0;}}

到：

    private Process.ProcessStartResult startProcess(HostingRecord hostingRecord, String entryPoint,ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,String seInfo, String requiredAbi, String instructionSet, String invokeWith,long startTime) {........................................} else {startResult = Process.start(entryPoint,app.processName, uid, uid, gids, runtimeFlags, mountExternal,app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,app.info.dataDir, invokeWith, app.info.packageName,new String[] {PROC_START_SEQ_IDENT + app.startSeq});}checkSlow(startTime, "startProcess: returned from zygote!");return startResult;} finally {Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);}}

Process.java

    public static ProcessStartResult start(@NonNull final String processClass,@Nullable final String niceName,int uid, int gid, @Nullable int[] gids,int runtimeFlags,int mountExternal,int targetSdkVersion,@Nullable String seInfo,@NonNull String abi,@Nullable String instructionSet,@Nullable String appDataDir,@Nullable String invokeWith,@Nullable String packageName,@Nullable String[] zygoteArgs) {return ZYGOTE_PROCESS.start(processClass, niceName, uid, gid, gids,runtimeFlags, mountExternal, targetSdkVersion, seInfo,abi, instructionSet, appDataDir, invokeWith, packageName,/*useUsapPool=*/ true, zygoteArgs);}

ZygoteProcess.java

    public final Process.ProcessStartResult start(@NonNull final String processClass,final String niceName,int uid, int gid, @Nullable int[] gids,int runtimeFlags, int mountExternal,int targetSdkVersion,@Nullable String seInfo,@NonNull String abi,@Nullable String instructionSet,@Nullable String appDataDir,@Nullable String invokeWith,@Nullable String packageName,boolean useUsapPool,@Nullable String[] zygoteArgs) {// TODO (chriswailes): Is there a better place to check this value?if (fetchUsapPoolEnabledPropWithMinInterval()) {informZygotesOfUsapPoolStatus();}try {return startViaZygote(processClass, niceName, uid, gid, gids,runtimeFlags, mountExternal, targetSdkVersion, seInfo,abi, instructionSet, appDataDir, invokeWith, /*startChildZygote=*/ false,packageName, useUsapPool, zygoteArgs);} catch (ZygoteStartFailedEx ex) {Log.e(LOG_TAG,"Starting VM process through Zygote failed");throw new RuntimeException("Starting VM process through Zygote failed", ex);}}

到：

private Process.ProcessStartResult startViaZygote(@NonNull final String processClass,@Nullable final String niceName,final int uid, final int gid,@Nullable final int[] gids,int runtimeFlags, int mountExternal,int targetSdkVersion,@Nullable String seInfo,@NonNull String abi,@Nullable String instructionSet,@Nullable String appDataDir,@Nullable String invokeWith,boolean startChildZygote,@Nullable String packageName,boolean useUsapPool,@Nullable String[] extraArgs)throws ZygoteStartFailedEx {.......................................synchronized(mLock) {// The USAP pool can not be used if the application will not use the systems graphics// driver.  If that driver is requested use the Zygote application start path.return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi),useUsapPool,argsForZygote);}}

到：

    private Process.ProcessStartResult zygoteSendArgsAndGetResult(ZygoteState zygoteState, boolean useUsapPool, @NonNull ArrayList args)throws ZygoteStartFailedEx {...........................return attemptZygoteSendArgsAndGetResult(zygoteState, msgStr);}

到：

private Process.ProcessStartResult attemptZygoteSendArgsAndGetResult(ZygoteState zygoteState, String msgStr) throws ZygoteStartFailedEx {try {final BufferedWriter zygoteWriter = zygoteState.mZygoteOutputWriter;final DataInputStream zygoteInputStream = zygoteState.mZygoteInputStream;zygoteWriter.write(msgStr);zygoteWriter.flush();// Always read the entire result from the input stream to avoid leaving// bytes in the stream for future process starts to accidentally stumble// upon.Process.ProcessStartResult result = new Process.ProcessStartResult();result.pid = zygoteInputStream.readInt();result.usingWrapper = zygoteInputStream.readBoolean();if (result.pid < 0) {throw new ZygoteStartFailedEx("fork() failed");}return result;} catch (IOException ex) {zygoteState.close();Log.e(LOG_TAG, "IO Exception while communicating with Zygote - "+ ex.toString());throw new ZygoteStartFailedEx(ex);}}

到这里命令已经拼接好了，然后通过localsocket与Zygote进程通讯，然后Zygote孵化出APP进程，进程启动后会用jni方式调用ActivityThread的main方法。

第三阶段：APP进程启动初始化activityThread并且将自己绑定到AMS服务中去，接下来就是有AMS来管理APP进程。

ActivityThread.java

    public static void main(String[] args) {..........................ActivityThread thread = new ActivityThread();thread.attach(false, startSeq);..........................}

到：

    private void attach(boolean system, long startSeq) {sCurrentActivityThread = this;mSystemThread = system;if (!system) {android.ddm.DdmHandleAppName.setAppName("",UserHandle.myUserId());RuntimeInit.setApplicationObject(mAppThread.asBinder());final IActivityManager mgr = ActivityManager.getService();try {mgr.attachApplication(mAppThread, startSeq);} catch (RemoteException ex) {throw ex.rethrowFromSystemServer();}..............................}

ActivityManager.getService()是获取AMS的binder代理对象，通过它调用AMS的attachApplication方法。

ActivityManagerService.java

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

到：

    private final boolean attachApplicationLocked(IApplicationThread thread,int pid, int callingUid, long startSeq) {.................................thread.bindApplication(processName, appInfo, providers,instr2.mClass,profilerInfo, instr2.mArguments,instr2.mWatcher,instr2.mUiAutomationConnection, testMode,mBinderTransactionTrackingEnabled, enableTrackAllocation,isRestrictedBackupMode || !normalMode, app.isPersistent(),new Configuration(app.getWindowProcessController().getConfiguration()),app.compat, getCommonServicesLocked(app.isolated),mCoreSettingsObserver.getCoreSettingsLocked(),buildSerial, autofillOptions, contentCaptureOptions);.................................}

这里会调用IApplicationThread的bindApplication实际上就是通过进程通讯调用ApplicationThread的bindApplication方法。ApplicationThread是activityThread的内部类。

ActivityThread.java

        public final void bindApplication(String processName, ApplicationInfo appInfo,List 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, AutofillOptions autofillOptions,ContentCaptureOptions contentCaptureOptions) {.................................................data.buildSerial = buildSerial;data.autofillOptions = autofillOptions;data.contentCaptureOptions = contentCaptureOptions;sendMessage(H.BIND_APPLICATION, data);}

追踪消息类型BIND_APPLICATION定位到：

        public void handleMessage(Message msg) {if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));switch (msg.what) {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;...........................}

到：

    private void handleBindApplication(AppBindData data) {............................try {// If the app is being launched for full backup or restore, bring it up in// a restricted environment with the base application class.app = data.info.makeApplication(data.restrictedBackupMode, null);............................}

到这里application创建成功并且调用onCreate生命周期,详细可以追踪makeApplication方法内部。

第四阶段：进程已经启动application创建完毕后开始AMS接管后面工作。

回到ActivityManagerService的attachApplicationLocked方法

ActivityManagerService.java

    private final boolean attachApplicationLocked(IApplicationThread thread,int pid, int callingUid, long startSeq) {.................................if (normalMode) {try {didSomething = mAtmInternal.attachApplication(app.getWindowProcessController());} catch (Exception e) {Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);badApp = true;}}.................................}

mAtmInternal就是ActivityTaskManagerService

ActivityTaskManagerService.java

        public boolean attachApplication(WindowProcessController wpc) throws RemoteException {synchronized (mGlobalLockWithoutBoost) {return mRootActivityContainer.attachApplication(wpc);}}

RootActivityContainer.java

boolean attachApplication(WindowProcessController app) throws RemoteException {final String processName = app.mName;boolean didSomething = false;for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {final ActivityDisplay display = mActivityDisplays.get(displayNdx);final ActivityStack stack = display.getFocusedStack();if (stack != null) {stack.getAllRunningVisibleActivitiesLocked(mTmpActivityList);final ActivityRecord top = stack.topRunningActivityLocked();final int size = mTmpActivityList.size();for (int i = 0; i < size; i++) {final ActivityRecord activity = mTmpActivityList.get(i);if (activity.app == null && app.mUid == activity.info.applicationInfo.uid&& processName.equals(activity.processName)) {try {if (mStackSupervisor.realStartActivityLocked(activity, app,top == activity /* andResume */, true /* checkConfig */)) {didSomething = true;}} catch (RemoteException e) {Slog.w(TAG, "Exception in new application when starting activity "+ top.intent.getComponent().flattenToShortString(), e);throw e;}}}}}if (!didSomething) {ensureActivitiesVisible(null, 0, false /* preserve_windows */);}return didSomething;}

ActivityStackSupervisor.java

    boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,boolean andResume, boolean checkConfig) throws RemoteException {.................................clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),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, proc.getReportedProcState(),r.icicle, r.persistentState, results, newIntents,dc.isNextTransitionForward(), proc.createProfilerInfoIfNeeded(),r.assistToken));.................................// Schedule transaction.mService.getLifecycleManager().scheduleTransaction(clientTransaction);.................................}

ClientLifecycleManager.java

    void scheduleTransaction(ClientTransaction transaction) throws RemoteException {final IApplicationThread client = transaction.getClient();transaction.schedule();if (!(client instanceof Binder)) {// If client is not an instance of Binder - it's a remote call and at this point it is// safe to recycle the object. All objects used for local calls will be recycled after// the transaction is executed on client in ActivityThread.transaction.recycle();}}

ClientTransaction.java

    public void schedule() throws RemoteException {mClient.scheduleTransaction(this);}

mClient是ApplicationThread代理，然后进程通讯到APP进程进入调用scheduleTransaction代码：

第五阶段：APP进程创建activity初始化调用生命周期onCreate。

ActivityThread.java

        public void scheduleTransaction(ClientTransaction transaction) throws RemoteException {ActivityThread.this.scheduleTransaction(transaction);}

这里会调用ActivityThread父类scheduleTransaction方法：

ClientTransactionHandler.java

    void scheduleTransaction(ClientTransaction transaction) {transaction.preExecute(this);sendMessage(ActivityThread.H.EXECUTE_TRANSACTION, transaction);}

跟踪ActivityThread.H.EXECUTE_TRANSACTION：

ActivityThread.java

                case EXECUTE_TRANSACTION:final ClientTransaction transaction = (ClientTransaction) msg.obj;mTransactionExecutor.execute(transaction);if (isSystem()) {// Client transactions inside system process are recycled on the client side// instead of ClientLifecycleManager to avoid being cleared before this// message is handled.transaction.recycle();}// TODO(lifecycler): Recycle locally scheduled transactions.break;

TransactionExecutor.java

    public void execute(ClientTransaction transaction) {...........................if (DEBUG_RESOLVER) Slog.d(TAG, transactionToString(transaction, mTransactionHandler));executeCallbacks(transaction);executeLifecycleState(transaction);mPendingActions.clear();if (DEBUG_RESOLVER) Slog.d(TAG, tId(transaction) + "End resolving transaction");}

到：

    public void executeCallbacks(ClientTransaction transaction) {.........................item.execute(mTransactionHandler, token, mPendingActions);item.postExecute(mTransactionHandler, token, mPendingActions);.........................}

item是前面ATMS中添加的类clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent)；

LaunchActivityItem.java

    public void execute(ClientTransactionHandler client, IBinder token,PendingTransactionActions pendingActions) {Trace.traceBegin(TRACE_TAG_ACTIVITY_MANAGER, "activityStart");ActivityClientRecord r = new ActivityClientRecord(token, mIntent, mIdent, mInfo,mOverrideConfig, mCompatInfo, mReferrer, mVoiceInteractor, mState, mPersistentState,mPendingResults, mPendingNewIntents, mIsForward,mProfilerInfo, client, mAssistToken);client.handleLaunchActivity(r, pendingActions, null /* customIntent */);Trace.traceEnd(TRACE_TAG_ACTIVITY_MANAGER);}

client就是ActivityThread：

ActivityThread.java

    public Activity handleLaunchActivity(ActivityClientRecord r,PendingTransactionActions pendingActions, Intent customIntent) {............................final Activity a = performLaunchActivity(r, customIntent);............................}

到：

    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {........................//创建上下文ContextImpl appContext = createBaseContextForActivity(r);.........................//反射创建activityactivity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);.........................//绑定applicationactivity.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,r.assistToken);.........................//触发生命周期mInstrumentation.callActivityOnCreate(activity, r.state);}

Instrumentation.java

    public void callActivityOnCreate(Activity activity, Bundle icicle) {prePerformCreate(activity);activity.performCreate(icicle);postPerformCreate(activity);}

Activity.java

    final void performCreate(Bundle icicle) {performCreate(icicle, null);}

到：

    final void performCreate(Bundle icicle, PersistableBundle persistentState) {dispatchActivityPreCreated(icicle);mCanEnterPictureInPicture = true;restoreHasCurrentPermissionRequest(icicle);if (persistentState != null) {onCreate(icicle, persistentState);} else {onCreate(icicle);}writeEventLog(LOG_AM_ON_CREATE_CALLED, "performCreate");mActivityTransitionState.readState(icicle);mVisibleFromClient = !mWindow.getWindowStyle().getBoolean(com.android.internal.R.styleable.Window_windowNoDisplay, false);mFragments.dispatchActivityCreated();mActivityTransitionState.setEnterActivityOptions(this, getActivityOptions());dispatchActivityPostCreated(icicle);}

最终调用我们属性onCreate生命周期