startActivity
Am
void run() throws RemoteException { try { printMessageForState(); mAm.setActivityController(this); mState = STATE_NORMAL; InputStreamReader converter = new InputStreamReader(System.in); BufferedReader in = new BufferedReader(converter); String line; while ((line = in.readLine()) != null) { boolean addNewline = true; if (line.length() <= 0) { addNewline = false; } else if ("q".equals(line) || "quit".equals(line)) { resumeController(RESULT_DEFAULT); break; } else if (mState == STATE_CRASHED) { if ("c".equals(line) || "continue".equals(line)) { resumeController(RESULT_CRASH_DIALOG); } else if ("k".equals(line) || "kill".equals(line)) { resumeController(RESULT_CRASH_KILL); } else { System.out.println("Invalid command: " + line); } } else if (mState == STATE_ANR) { if ("c".equals(line) || "continue".equals(line)) { resumeController(RESULT_ANR_DIALOG); } else if ("k".equals(line) || "kill".equals(line)) { resumeController(RESULT_ANR_KILL); } else if ("w".equals(line) || "wait".equals(line)) { resumeController(RESULT_ANR_WAIT); } else { System.out.println("Invalid command: " + line); } } else if (mState == STATE_EARLY_ANR) { if ("c".equals(line) || "continue".equals(line)) { resumeController(RESULT_EARLY_ANR_CONTINUE); } else if ("k".equals(line) || "kill".equals(line)) { resumeController(RESULT_EARLY_ANR_KILL); } else { System.out.println("Invalid command: " + line); } } else { System.out.println("Invalid command: " + line); } synchronized (this) { if (addNewline) { System.out.println(""); } printMessageForState(); } } } catch (IOException e) { e.printStackTrace(); } finally { mAm.setActivityController(null); } }
private void runStart() throws Exception { Intent intent = makeIntent(UserHandle.USER_CURRENT); if (mUserId == UserHandle.USER_ALL) { System.err.println("Error: Can't start service with user 'all'"); return; } String mimeType = intent.getType(); if (mimeType == null && intent.getData() != null && "content".equals(intent.getData().getScheme())) { mimeType = mAm.getProviderMimeType(intent.getData(), mUserId); } do { if (mStopOption) { String packageName; if (intent.getComponent() != null) { packageName = intent.getComponent().getPackageName(); } else { IPackageManager pm = IPackageManager.Stub.asInterface( ServiceManager.getService("package")); if (pm == null) { System.err.println("Error: Package manager not running; aborting"); return; } List<ResolveInfo> activities = pm.queryIntentActivities(intent, mimeType, 0, mUserId); if (activities == null || activities.size() <= 0) { System.err.println("Error: Intent does not match any activities: " + intent); return; } else if (activities.size() > 1) { System.err.println("Error: Intent matches multiple activities; can't stop: " + intent); return; } packageName = activities.get(0).activityInfo.packageName; } System.out.println("Stopping: " + packageName); mAm.forceStopPackage(packageName, mUserId); Thread.sleep(250); } System.out.println("Starting: " + intent); intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); ParcelFileDescriptor fd = null; ProfilerInfo profilerInfo = null; if (mProfileFile != null) { try { fd = openForSystemServer( new File(mProfileFile), ParcelFileDescriptor.MODE_CREATE | ParcelFileDescriptor.MODE_TRUNCATE | ParcelFileDescriptor.MODE_READ_WRITE); } catch (FileNotFoundException e) { System.err.println("Error: Unable to open file: " + mProfileFile); System.err.println("Consider using a file under /data/local/tmp/"); return; } profilerInfo = new ProfilerInfo(mProfileFile, fd, mSamplingInterval, mAutoStop); } IActivityManager.WaitResult result = null; int res; final long startTime = SystemClock.uptimeMillis(); if (mWaitOption) { result = mAm.startActivityAndWait(null, null, intent, mimeType, null, null, 0, mStartFlags, profilerInfo, null, mUserId); res = result.result; } else { res = mAm.startActivityAsUser(null, null, intent, mimeType, null, null, 0, mStartFlags, profilerInfo, null, mUserId); } final long endTime = SystemClock.uptimeMillis(); PrintStream out = mWaitOption ? System.out : System.err; boolean launched = false; switch (res) { case ActivityManager.START_SUCCESS: launched = true; break; case ActivityManager.START_SWITCHES_CANCELED: launched = true; out.println( "Warning: Activity not started because the " + " current activity is being kept for the user."); break; case ActivityManager.START_DELIVERED_TO_TOP: launched = true; out.println( "Warning: Activity not started, intent has " + "been delivered to currently running " + "top-most instance."); break; case ActivityManager.START_RETURN_INTENT_TO_CALLER: launched = true; out.println( "Warning: Activity not started because intent " + "should be handled by the caller"); break; case ActivityManager.START_TASK_TO_FRONT: launched = true; out.println( "Warning: Activity not started, its current " + "task has been brought to the front"); break; case ActivityManager.START_INTENT_NOT_RESOLVED: out.println( "Error: Activity not started, unable to " + "resolve " + intent.toString()); break; case ActivityManager.START_CLASS_NOT_FOUND: out.println(NO_CLASS_ERROR_CODE); out.println("Error: Activity class " + intent.getComponent().toShortString() + " does not exist."); break; case ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT: out.println( "Error: Activity not started, you requested to " + "both forward and receive its result"); break; case ActivityManager.START_PERMISSION_DENIED: out.println( "Error: Activity not started, you do not " + "have permission to access it."); break; case ActivityManager.START_NOT_VOICE_COMPATIBLE: out.println( "Error: Activity not started, voice control not allowed for: " + intent); break; case ActivityManager.START_NOT_CURRENT_USER_ACTIVITY: out.println( "Error: Not allowed to start background user activity" + " that shouldn't be displayed for all users."); break; default: out.println( "Error: Activity not started, unknown error code " + res); break; } if (mWaitOption && launched) { if (result == null) { result = new IActivityManager.WaitResult(); result.who = intent.getComponent(); } System.out.println("Status: " + (result.timeout ? "timeout" : "ok")); if (result.who != null) { System.out.println("Activity: " + result.who.flattenToShortString()); } if (result.thisTime >= 0) { System.out.println("ThisTime: " + result.thisTime); } if (result.totalTime >= 0) { System.out.println("TotalTime: " + result.totalTime); } System.out.println("WaitTime: " + (endTime-startTime)); System.out.println("Complete"); } mRepeat--; if (mRepeat > 1) { mAm.unhandledBack(); } } while (mRepeat > 1); }
am最终将调用AMS的startActivityAndWait函数来处理这次启动请求。
@Override public final WaitResult startActivityAndWait(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) { enforceNotIsolatedCaller("startActivityAndWait"); userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId, false, ALLOW_FULL_ONLY, "startActivityAndWait", null); WaitResult res = new WaitResult(); // TODO: Switch to user app stacks here. mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent, resolvedType, null, null, resultTo, resultWho, requestCode, startFlags, profilerInfo, res, null, options, false, userId, null, null); return res; }
final void startActivityLocked(ActivityRecord r, boolean newTask, boolean doResume, boolean keepCurTransition, Bundle options) { TaskRecord rTask = r.task; final int taskId = rTask.taskId; // mLaunchTaskBehind tasks get placed at the back of the task stack. if (!r.mLaunchTaskBehind && (taskForIdLocked(taskId) == null || newTask)) { // Last activity in task had been removed or ActivityManagerService is reusing task. // Insert or replace. // Might not even be in. insertTaskAtTop(rTask, r); mWindowManager.moveTaskToTop(taskId); } TaskRecord task = null; if (!newTask) { // If starting in an existing task, find where that is... boolean startIt = true; for (int taskNdx = mTaskHistory.size() - 1; taskNdx >= 0; --taskNdx) { task = mTaskHistory.get(taskNdx); if (task.getTopActivity() == null) { // All activities in task are finishing. continue; } if (task == r.task) { // Here it is! Now, if this is not yet visible to the // user, then just add it without starting; it will // get started when the user navigates back to it. if (!startIt) { if (DEBUG_ADD_REMOVE) Slog.i(TAG, "Adding activity " + r + " to task " + task, new RuntimeException("here").fillInStackTrace()); task.addActivityToTop(r); r.putInHistory(); mWindowManager.addAppToken(task.mActivities.indexOf(r), r.appToken, r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen, (r.info.flags & ActivityInfo.FLAG_SHOW_FOR_ALL_USERS) != 0, r.userId, r.info.configChanges, task.voiceSession != null, r.mLaunchTaskBehind); if (VALIDATE_TOKENS) { validateAppTokensLocked(); } ActivityOptions.abort(options); return; } break; } else if (task.numFullscreen > 0) { startIt = false; } } } // Place a new activity at top of stack, so it is next to interact // with the user. // If we are not placing the new activity frontmost, we do not want // to deliver the onUserLeaving callback to the actual frontmost // activity if (task == r.task && mTaskHistory.indexOf(task) != (mTaskHistory.size() - 1)) { mStackSupervisor.mUserLeaving = false; if (DEBUG_USER_LEAVING) Slog.v(TAG_USER_LEAVING, "startActivity() behind front, mUserLeaving=false"); } task = r.task; // Slot the activity into the history stack and proceed if (DEBUG_ADD_REMOVE) Slog.i(TAG, "Adding activity " + r + " to stack to task " + task, new RuntimeException("here").fillInStackTrace()); task.addActivityToTop(r); task.setFrontOfTask(); r.putInHistory(); if (!isHomeStack() || numActivities() > 0) { // We want to show the starting preview window if we are // switching to a new task, or the next activity's process is // not currently running. boolean showStartingIcon = newTask; ProcessRecord proc = r.app; if (proc == null) { proc = mService.mProcessNames.get(r.processName, r.info.applicationInfo.uid); } if (proc == null || proc.thread == null) { showStartingIcon = true; } if (DEBUG_TRANSITION) Slog.v(TAG_TRANSITION, "Prepare open transition: starting " + r); if ((r.intent.getFlags() & Intent.FLAG_ACTIVITY_NO_ANIMATION) != 0) { mWindowManager.prepareAppTransition(AppTransition.TRANSIT_NONE, keepCurTransition); mNoAnimActivities.add(r); } else { mWindowManager.prepareAppTransition(newTask ? r.mLaunchTaskBehind ? AppTransition.TRANSIT_TASK_OPEN_BEHIND : AppTransition.TRANSIT_TASK_OPEN : AppTransition.TRANSIT_ACTIVITY_OPEN, keepCurTransition); mNoAnimActivities.remove(r); } mWindowManager.addAppToken(task.mActivities.indexOf(r), r.appToken, r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen, (r.info.flags & ActivityInfo.FLAG_SHOW_FOR_ALL_USERS) != 0, r.userId, r.info.configChanges, task.voiceSession != null, r.mLaunchTaskBehind); boolean doShow = true; if (newTask) { // Even though this activity is starting fresh, we still need // to reset it to make sure we apply affinities to move any // existing activities from other tasks in to it. // If the caller has requested that the target task be // reset, then do so. if ((r.intent.getFlags() & Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED) != 0) { resetTaskIfNeededLocked(r, r); doShow = topRunningNonDelayedActivityLocked(null) == r; } } else if (options != null && new ActivityOptions(options).getAnimationType() == ActivityOptions.ANIM_SCENE_TRANSITION) { doShow = false; } if (r.mLaunchTaskBehind) { // Don't do a starting window for mLaunchTaskBehind. More importantly make sure we // tell WindowManager that r is visible even though it is at the back of the stack. mWindowManager.setAppVisibility(r.appToken, true); ensureActivitiesVisibleLocked(null, 0); } else if (SHOW_APP_STARTING_PREVIEW && doShow) { // Figure out if we are transitioning from another activity that is // "has the same starting icon" as the next one. This allows the // window manager to keep the previous window it had previously // created, if it still had one. ActivityRecord prev = mResumedActivity; if (prev != null) { // We don't want to reuse the previous starting preview if: // (1) The current activity is in a different task. if (prev.task != r.task) { prev = null; } // (2) The current activity is already displayed. else if (prev.nowVisible) { prev = null; } } mWindowManager.setAppStartingWindow( r.appToken, r.packageName, r.theme, mService.compatibilityInfoForPackageLocked( r.info.applicationInfo), r.nonLocalizedLabel, r.labelRes, r.icon, r.logo, r.windowFlags, prev != null ? prev.appToken : null, showStartingIcon); r.mStartingWindowShown = true; } } else { // If this is the first activity, don't do any fancy animations, // because there is nothing for it to animate on top of. mWindowManager.addAppToken(task.mActivities.indexOf(r), r.appToken, r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen, (r.info.flags & ActivityInfo.FLAG_SHOW_FOR_ALL_USERS) != 0, r.userId, r.info.configChanges, task.voiceSession != null, r.mLaunchTaskBehind); ActivityOptions.abort(options); options = null; } if (VALIDATE_TOKENS) { validateAppTokensLocked(); } if (doResume) { mStackSupervisor.resumeTopActivitiesLocked(this, r, options); } }
startActivityLocked函数的主要工作包括
1.处理sourceRecord及resultRecord。其中，sourceRecord表示发起本次请求的Activity，resultRecord表示接收处理结果的Activity（启动一个Activity肯定需要它完成某项事情，当目标Activity将事情成后，就需要告知请求者该事情的处理结果）。在一般情况下，sourceRecord和resultRecord应指向同一个Activity。
2.处理app switch。如果AMS当前禁止app switch，则只能把本次启动请求保存起来，以待允许app switch时再处理。从代码中可知，AMS在处理本次请求前，会先调用doPendingActivityLaunchesLocked函数，在该函数内部将启动之前因系统禁止app switch而保存的Pending请求
3.调用startActivityUncheckedLocked处理本次Activity启动请求
@Override public void stopAppSwitches() { if (checkCallingPermission(android.Manifest.permission.STOP_APP_SWITCHES) != PackageManager.PERMISSION_GRANTED) { throw new SecurityException("Requires permission " + android.Manifest.permission.STOP_APP_SWITCHES); } synchronized(this) { mAppSwitchesAllowedTime = SystemClock.uptimeMillis() + APP_SWITCH_DELAY_TIME; mDidAppSwitch = false; mHandler.removeMessages(DO_PENDING_ACTIVITY_LAUNCHES_MSG); Message msg = mHandler.obtainMessage(DO_PENDING_ACTIVITY_LAUNCHES_MSG); mHandler.sendMessageDelayed(msg, APP_SWITCH_DELAY_TIME); } }
public void resumeAppSwitches() { if (checkCallingPermission(android.Manifest.permission.STOP_APP_SWITCHES) != PackageManager.PERMISSION_GRANTED) { throw new SecurityException("Requires permission " + android.Manifest.permission.STOP_APP_SWITCHES); } synchronized(this) { // Note that we don't execute any pending app switches... we will // let those wait until either the timeout, or the next start // activity request. mAppSwitchesAllowedTime = 0; } }
startActivityUncheckedLocked函数很长，但是目的比较简单，即为新创建的ActivityRecord找到一个合适的Task。
ActivityStack
final boolean resumeTopActivityLocked(ActivityRecord prev, Bundle options) { if (mStackSupervisor.inResumeTopActivity) { // Don't even start recursing. return false; } boolean result = false; try { // Protect against recursion. mStackSupervisor.inResumeTopActivity = true; if (mService.mLockScreenShown == ActivityManagerService.LOCK_SCREEN_LEAVING) { mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_HIDDEN; mService.updateSleepIfNeededLocked(); } result = resumeTopActivityInnerLocked(prev, options); } finally { mStackSupervisor.inResumeTopActivity = false; } return result; }
resumeTopActivityLocked函数中有两个非常重要的关键点
1.如果mResumedActivity不为空，则需要先暂停（pause）这个Activity。由代码中的注释可知，mResumedActivity代表上一次启动的（即当前正显示的）Activity。现在要启动一个新的Activity，须先停止当前Activity，这部分工作由startPausingLocked函数完成
2.mResumeActivity什么时候为空呢？当然是在启动全系统第一个Activity时，即启动Home界面的时候。除此之外，该值都不会为空
resumeTopActivityLocked最后将调用另外一个startSpecificActivityLocked，该函数将真正创建一个应用进程。
private final void startProcessLocked(ProcessRecord app, String hostingType, String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) { long startTime = SystemClock.elapsedRealtime(); if (app.pid > 0 && app.pid != MY_PID) { checkTime(startTime, "startProcess: removing from pids map"); synchronized (mPidsSelfLocked) { mPidsSelfLocked.remove(app.pid); mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app); } checkTime(startTime, "startProcess: done removing from pids map"); app.setPid(0); } if (DEBUG_PROCESSES && mProcessesOnHold.contains(app)) Slog.v(TAG_PROCESSES, "startProcessLocked removing on hold: " + app); mProcessesOnHold.remove(app); checkTime(startTime, "startProcess: starting to update cpu stats"); updateCpuStats(); checkTime(startTime, "startProcess: done updating cpu stats"); try { try { if (AppGlobals.getPackageManager().isPackageFrozen(app.info.packageName)) { // This is caught below as if we had failed to fork zygote throw new RuntimeException("Package " + app.info.packageName + " is frozen!"); } } catch (RemoteException e) { throw e.rethrowAsRuntimeException(); } int uid = app.uid; int[] gids = null; int mountExternal = Zygote.MOUNT_EXTERNAL_NONE; if (!app.isolated) { int[] permGids = null; try { checkTime(startTime, "startProcess: getting gids from package manager"); final IPackageManager pm = AppGlobals.getPackageManager(); permGids = pm.getPackageGids(app.info.packageName, app.userId); MountServiceInternal mountServiceInternal = LocalServices.getService( MountServiceInternal.class); mountExternal = mountServiceInternal.getExternalStorageMountMode(uid, app.info.packageName); } catch (RemoteException e) { throw e.rethrowAsRuntimeException(); } /* * Add shared application and profile GIDs so applications can share some * resources like shared libraries and access user-wide resources */ if (ArrayUtils.isEmpty(permGids)) { gids = new int[2]; } else { gids = new int[permGids.length + 2]; System.arraycopy(permGids, 0, gids, 2, permGids.length); } gids[0] = UserHandle.getSharedAppGid(UserHandle.getAppId(uid)); gids[1] = UserHandle.getUserGid(UserHandle.getUserId(uid)); } checkTime(startTime, "startProcess: building args"); if (mFactoryTest != FactoryTest.FACTORY_TEST_OFF) { if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL && mTopComponent != null && app.processName.equals(mTopComponent.getPackageName())) { uid = 0; } if (mFactoryTest == FactoryTest.FACTORY_TEST_HIGH_LEVEL && (app.info.flags&ApplicationInfo.FLAG_FACTORY_TEST) != 0) { uid = 0; } } int debugFlags = 0; if ((app.info.flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0) { debugFlags |= Zygote.DEBUG_ENABLE_DEBUGGER; // Also turn on CheckJNI for debuggable apps. It's quite // awkward to turn on otherwise. debugFlags |= Zygote.DEBUG_ENABLE_CHECKJNI; } // Run the app in safe mode if its manifest requests so or the // system is booted in safe mode. if ((app.info.flags & ApplicationInfo.FLAG_VM_SAFE_MODE) != 0 || mSafeMode == true) { debugFlags |= Zygote.DEBUG_ENABLE_SAFEMODE; } if ("1".equals(SystemProperties.get("debug.checkjni"))) { debugFlags |= Zygote.DEBUG_ENABLE_CHECKJNI; } String jitDebugProperty = SystemProperties.get("debug.usejit"); if ("true".equals(jitDebugProperty)) { debugFlags |= Zygote.DEBUG_ENABLE_JIT; } else if (!"false".equals(jitDebugProperty)) { // If we didn't force disable by setting false, defer to the dalvik vm options. if ("true".equals(SystemProperties.get("dalvik.vm.usejit"))) { debugFlags |= Zygote.DEBUG_ENABLE_JIT; } } String genDebugInfoProperty = SystemProperties.get("debug.generate-debug-info"); if ("true".equals(genDebugInfoProperty)) { debugFlags |= Zygote.DEBUG_GENERATE_DEBUG_INFO; } if ("1".equals(SystemProperties.get("debug.jni.logging"))) { debugFlags |= Zygote.DEBUG_ENABLE_JNI_LOGGING; } if ("1".equals(SystemProperties.get("debug.assert"))) { debugFlags |= Zygote.DEBUG_ENABLE_ASSERT; } String requiredAbi = (abiOverride != null) ? abiOverride : app.info.primaryCpuAbi; if (requiredAbi == null) { requiredAbi = Build.SUPPORTED_ABIS[0]; } String instructionSet = null; if (app.info.primaryCpuAbi != null) { instructionSet = VMRuntime.getInstructionSet(app.info.primaryCpuAbi); } app.gids = gids; app.requiredAbi = requiredAbi; app.instructionSet = instructionSet; // Start the process. It will either succeed and return a result containing // the PID of the new process, or else throw a RuntimeException. boolean isActivityProcess = (entryPoint == null); if (entryPoint == null) entryPoint = "android.app.ActivityThread"; Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " + app.processName); checkTime(startTime, "startProcess: asking zygote to start proc"); Process.ProcessStartResult startResult = Process.start(entryPoint, app.processName, uid, uid, gids, debugFlags, mountExternal, app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet, app.info.dataDir, entryPointArgs); checkTime(startTime, "startProcess: returned from zygote!"); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); if (app.isolated) { mBatteryStatsService.addIsolatedUid(app.uid, app.info.uid); } mBatteryStatsService.noteProcessStart(app.processName, app.info.uid); checkTime(startTime, "startProcess: done updating battery stats"); EventLog.writeEvent(EventLogTags.AM_PROC_START, UserHandle.getUserId(uid), startResult.pid, uid, app.processName, hostingType, hostingNameStr != null ? hostingNameStr : ""); if (app.persistent) { Watchdog.getInstance().processStarted(app.processName, startResult.pid); } checkTime(startTime, "startProcess: building log message"); StringBuilder buf = mStringBuilder; buf.setLength(0); buf.append("Start proc "); buf.append(startResult.pid); buf.append(':'); buf.append(app.processName); buf.append('/'); UserHandle.formatUid(buf, uid); if (!isActivityProcess) { buf.append(" ["); buf.append(entryPoint); buf.append("]"); } buf.append(" for "); buf.append(hostingType); if (hostingNameStr != null) { buf.append(" "); buf.append(hostingNameStr); } Slog.i(TAG, buf.toString()); app.setPid(startResult.pid); app.usingWrapper = startResult.usingWrapper; app.removed = false; app.killed = false; app.killedByAm = false; checkTime(startTime, "startProcess: starting to update pids map"); synchronized (mPidsSelfLocked) { this.mPidsSelfLocked.put(startResult.pid, app); if (isActivityProcess) { Message msg = mHandler.obtainMessage(PROC_START_TIMEOUT_MSG); msg.obj = app; mHandler.sendMessageDelayed(msg, startResult.usingWrapper ? PROC_START_TIMEOUT_WITH_WRAPPER : PROC_START_TIMEOUT); } } checkTime(startTime, "startProcess: done updating pids map"); } catch (RuntimeException e) { // XXX do better error recovery. app.setPid(0); mBatteryStatsService.noteProcessFinish(app.processName, app.info.uid); if (app.isolated) { mBatteryStatsService.removeIsolatedUid(app.uid, app.info.uid); } Slog.e(TAG, "Failure starting process " + app.processName, e); } }
1.FLAG_FROM_BACKGROUND标志发起这次启动的Task属于后台任务。很显然，手机中没有界面供用户操作位于后台Task中的Activity。如果没有设置该标志，那么这次启动请求就是由前台Task因某种原因而触发的（例如：用户单击某个按钮）
2.如果一个应用进程在1分钟内连续崩溃超过2次，则AMS会将其ProcessRecord加入所谓的mBadProcesses中。一个应用崩溃后，系统会弹出一个警告框以提醒用户。
ActivityThread
public static void main(String[] args) { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain"); SamplingProfilerIntegration.start(); // CloseGuard defaults to true and can be quite spammy. We // disable it here, but selectively enable it later (via // StrictMode) on debug builds, but using DropBox, not logs. CloseGuard.setEnabled(false); Environment.initForCurrentUser(); // Set the reporter for event logging in libcore EventLogger.setReporter(new EventLoggingReporter()); AndroidKeyStoreProvider.install(); // Make sure TrustedCertificateStore looks in the right place for CA certificates 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(new LogPrinter(Log.DEBUG, "ActivityThread")); } // End of event ActivityThreadMain. Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); }
在main函数内部将创建一个消息循环Loop，接着调用ActivityThread的attach函数，最终将主线程加入消息循环
private void attach(boolean system) { sCurrentActivityThread = this; mSystemThread = system; if (!system) { ViewRootImpl.addFirstDrawHandler(new Runnable() { @Override public void run() { ensureJitEnabled(); } }); android.ddm.DdmHandleAppName.setAppName("<pre-initialized>", UserHandle.myUserId()); RuntimeInit.setApplicationObject(mAppThread.asBinder()); final IActivityManager mgr = ActivityManagerNative.getDefault(); try { mgr.attachApplication(mAppThread); } catch (RemoteException ex) { // Ignore } // Watch for getting close to heap limit. BinderInternal.addGcWatcher(new Runnable() { @Override public void run() { if (!mSomeActivitiesChanged) { return; } Runtime runtime = Runtime.getRuntime(); long dalvikMax = runtime.maxMemory(); long dalvikUsed = runtime.totalMemory() - runtime.freeMemory(); if (dalvikUsed > ((3*dalvikMax)/4)) { if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024) + " total=" + (runtime.totalMemory()/1024) + " used=" + (dalvikUsed/1024)); mSomeActivitiesChanged = false; try { mgr.releaseSomeActivities(mAppThread); } catch (RemoteException e) { } } } }); } else { // Don't set application object here -- if the system crashes, // we can't display an alert, we just want to die die die. android.ddm.DdmHandleAppName.setAppName("system_process", UserHandle.myUserId()); try { mInstrumentation = new Instrumentation(); ContextImpl context = ContextImpl.createAppContext( this, getSystemContext().mPackageInfo); mInitialApplication = context.mPackageInfo.makeApplication(true, null); mInitialApplication.onCreate(); } catch (Exception e) { throw new RuntimeException( "Unable to instantiate Application():" + e.toString(), e); } } // add dropbox logging to libcore DropBox.setReporter(new DropBoxReporter()); ViewRootImpl.addConfigCallback(new ComponentCallbacks2() { @Override public void onConfigurationChanged(Configuration newConfig) { synchronized (mResourcesManager) { // We need to apply this change to the resources // immediately, because upon returning the view // hierarchy will be informed about it. if (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, null)) { // This actually changed the resources! Tell // everyone about it. if (mPendingConfiguration == null || mPendingConfiguration.isOtherSeqNewer(newConfig)) { mPendingConfiguration = newConfig; sendMessage(H.CONFIGURATION_CHANGED, newConfig); } } } } @Override public void onLowMemory() { } @Override public void onTrimMemory(int level) { } }); }
AMS创建一个应用进程后，会设置一个超时时间（一般是10秒）。如果超过这个时间，应用进程还没有和AMS交互，则断定该进程创建失败。所以，应用进程启动后，需要尽快和AMS交互，即调用AMS的attachApplication函数。在该函数内部将调用attachApplicationLocked。
attachApplicationLocked第一阶段的工作比较简单：
1.设置代表该应用进程的ProcessRecord对象的一些成员变量，如用于和应用进程交互的thread对象、jincheng 调度优先级及oom_adj的值等
2.从消息队列中撤销PROC_START_TIMEOUT_MSG
应用进程的创建及初始化总结
1.在应用进程启动后，需要尽快调用AMS的attachApplication函数，该函数是这个刚创建的应用进程第一次和AMS交互。此时的它还默默无名，连一个确定的进程名都没有。不过没关系，attachApplication函数将根据创建该应用进程之前所保存的ProcessRecord为其准备一切手续
2.attachApplication准备好一切后，将调用应用进程的bindApplication函数，在该函数内部将发消息给主线程，最终该消息由handleBindApplication处理。handleBindApplication将为该进程设置进程名，初始化一些策略和参数信息等。另外，它还创建一个Application对象。同时，如果该Application声明了ContentProvider，还需要为该进程安装ContentProvider。
AMS调用完bindApplication后，将通过realStartActivityLocked启动Activity。在此之前，要创建完应用进程并初始化Android运行环境
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) { // If we are getting ready to gc after going to the background, well // we are back active so skip it. unscheduleGcIdler(); mSomeActivitiesChanged = true; if (r.profilerInfo != null) { mProfiler.setProfiler(r.profilerInfo); mProfiler.startProfiling(); } // Make sure we are running with the most recent config. handleConfigurationChanged(null, null); if (localLOGV) Slog.v( TAG, "Handling launch of " + r); // Initialize before creating the activity WindowManagerGlobal.initialize(); Activity a = performLaunchActivity(r, customIntent); if (a != null) { r.createdConfig = new Configuration(mConfiguration); Bundle oldState = r.state; handleResumeActivity(r.token, false, r.isForward, !r.activity.mFinished && !r.startsNotResumed); if (!r.activity.mFinished && r.startsNotResumed) { // The activity manager actually wants this one to start out // paused, because it needs to be visible but isn't in the // foreground. We accomplish this by going through the // normal startup (because activities expect to go through // onResume() the first time they run, before their window // is displayed), and then pausing it. However, in this case // we do -not- need to do the full pause cycle (of freezing // and such) because the activity manager assumes it can just // retain the current state it has. try { r.activity.mCalled = false; mInstrumentation.callActivityOnPause(r.activity); // We need to keep around the original state, in case // we need to be created again. But we only do this // for pre-Honeycomb apps, which always save their state // when pausing, so we can not have them save their state // when restarting from a paused state. For HC and later, // we want to (and can) let the state be saved as the normal // part of stopping the activity. if (r.isPreHoneycomb()) { r.state = oldState; } if (!r.activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onPause()"); } } catch (SuperNotCalledException e) { throw e; } catch (Exception e) { if (!mInstrumentation.onException(r.activity, e)) { throw new RuntimeException( "Unable to pause activity " + r.intent.getComponent().toShortString() + ": " + e.toString(), e); } } r.paused = true; } } else { // If there was an error, for any reason, tell the activity // manager to stop us. try { ActivityManagerNative.getDefault() .finishActivity(r.token, Activity.RESULT_CANCELED, null, false); } catch (RemoteException ex) { // Ignore } } }
1.首先调用performLaunchActivity，该在函数内部通过Java反射机制创建目标Activity，然后调用它的onCreate及onStart函数
2.调用handleResumeActivity，会在其内部调用目标Activity的onResume函数。
startActivity总结
1.起点是am。我们利用am start命令，发起本次目标Activity的启动请求
2.接下来进入ActivityManagerService和ActivityStack这两个核心类。对于启动Activity来说，这段行程又可细分为两个阶段：第一阶段就是根据启动模式和启动标志找到活创建ActivityRecord及对应的TaskRecord；第二阶段就是处理Activity启动或切换相关的工作
3.然后AMS直接创建目标进程并运行Activity的流程，其中涉及目标进程的创建，目标进程中Android运行环境的初始化，目标Activity的创建以及onCreate、onStart及onResume等生命周期中重要函数的调用等相关知识
4.AMS先暂停当前Activity，然后再创建目标进程并运行Activity的流程，其中两个应用进程和AMS交互。