前言
今天接着完善Android系统这一块的体系架构,说说在App启动流程中举足轻重的ActivityManagerService。
顾名思义,这个组件肯定是用来管理Activity的服务,其实不仅是Activity,它还负责四大组件相关的启动,切换,调度等等。
具体是怎么被启动的,又是怎么进行管理的呢?一起看看吧。
(代码基于Android9.0)
服务的启动
之前在SystemServer章节说过,系统的服务一般都是通过SystemServer进程启动的,AMS也不例外。
- //SystemServer.java
- private void startBootstrapServices() {
- //...
- // Activity manager runs the show.
- traceBeginAndSlog("StartActivityManager");
- mActivityManagerService = mSystemServiceManager.startService(
- ActivityManagerService.Lifecycle.class).getService();
- mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
- mActivityManagerService.setInstaller(installer);
- traceEnd();
- }
- //中间用到了反射,之前说过。
- public void startService(@NonNull final SystemService service) {
- // Register it.
- mServices.add(service);
- // Start it.
- long time = SystemClock.elapsedRealtime();
- try {
- service.onStart();
- } catch (RuntimeException ex) {
- throw new RuntimeException("Failed to start service " + service.getClass().getName()
- + ": onStart threw an exception", ex);
- }
- }
- //ActivityManagerService.java
- public static final class Lifecycle extends SystemService {
- private final ActivityManagerService mService;
- public Lifecycle(Context context) {
- super(context);
- mService = new ActivityManagerService(context);
- }
- @Override
- public void onStart() {
- mService.start();
- }
- @Override
- public void onBootPhase(int phase) {
- mService.mBootPhase = phase;
- if (phase == PHASE_SYSTEM_SERVICES_READY) {
- mService.mBatteryStatsService.systemServicesReady();
- mService.mServices.systemServicesReady();
- }
- }
- @Override
- public void onCleanupUser(int userId) {
- mService.mBatteryStatsService.onCleanupUser(userId);
- }
- public ActivityManagerService getService() {
- return mService;
- }
- }
可以看到,通过调用了ActivityManagerService.Lifecycle这个内部类中的onStart方法,启动了AMS,并调用了AMS的start方法。
再简单看看AMS的实例化方法和start方法:
- public ActivityManagerService(Context systemContext) {
- mContext = systemContext;
- mFactoryTest = FactoryTest.getMode();
- mSystemThread = ActivityThread.currentActivityThread();
- mUiContext = mSystemThread.getSystemUiContext();
- mHandlerThread = new ServiceThread(TAG,
- THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
- mHandlerThread.start();
- mHandler = new MainHandler(mHandlerThread.getLooper());
- mUiHandler = mInjector.getUiHandler(this);
- //...
- mServices = new ActiveServices(this);
- mProviderMap = new ProviderMap(this);
- mAppErrors = new AppErrors(mUiContext, this);
- // TODO: Move creation of battery stats service outside of activity manager service.
- mBatteryStatsService = new BatteryStatsService(systemContext, systemDir, mHandler);
- mBatteryStatsService.getActiveStatistics().readLocked();
- mBatteryStatsService.scheduleWriteToDisk();
- mOnBattery = DEBUG_POWER ? true
- : mBatteryStatsService.getActiveStatistics().getIsOnBattery();
- mBatteryStatsService.getActiveStatistics().setCallback(this);
- mStackSupervisor = createStackSupervisor();
- mStackSupervisor.onConfigurationChanged(mTempConfig);
- mActivityStartController = new ActivityStartController(this);
- mRecentTasks = createRecentTasks();
- mStackSupervisor.setRecentTasks(mRecentTasks);
- mLockTaskController = new LockTaskController(mContext, mStackSupervisor, mHandler);
- mLifecycleManager = new ClientLifecycleManager();
- mProcessCpuThread = new Thread("CpuTracker")
- //...
- }
- private void start() {
- removeAllProcessGroups();
- mProcessCpuThread.start();
- mBatteryStatsService.publish();
- mAppOpsService.publish(mContext);
- Slog.d("AppOps", "AppOpsService published");
- LocalServices.addService(ActivityManagerInternal.class, new LocalService());
- // Wait for the synchronized block started in mProcessCpuThread,
- // so that any other acccess to mProcessCpuTracker from main thread
- // will be blocked during mProcessCpuTracker initialization.
- try {
- mProcessCpuInitLatch.await();
- } catch (InterruptedException e) {
- Slog.wtf(TAG, "Interrupted wait during start", e);
- Thread.currentThread().interrupt();
- throw new IllegalStateException("Interrupted wait during start");
- }
- }
代码很长,我只截取了一部分。
在构造函数中,主要初始化了一些对象,比如Context、ActivityThrad、Handler、CPU监控线程,还有一些后文要用到的ActivityStackSupervisor、ActivityStarter等对象,
在start方法中,主要就是启动了CPU监控线程,然后注册了电池状态服务和权限管理服务。
初始工作
AMS被启动之后,还会在SystemServer启动三大服务的时候偷偷干一些工作,我们搜索下mActivityManagerService变量就可以看到:
- private void startBootstrapServices() {
- //1、初始化电源管理器
- mActivityManagerService.initPowerManagement();
- //2、为系统进程设置应用程序实例并启动。
- mActivityManagerService.setSystemProcess();
- }
- private void startCoreServices() {
- // 启动UsageStatsManager,用于查询应用的使用情况
- mSystemServiceManager.startService(UsageStatsService.class);
- mActivityManagerService.setUsageStatsManager(
- LocalServices.getService(UsageStatsManagerInternal.class));
- traceEnd();
- }
- private void startOtherServices() {
- //安装系统的Providers
- mActivityManagerService.installSystemProviders();
- //启动WMS,并为AMS设置WMS关系
- wm = WindowManagerService.main(context, inputManager,
- mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
- !mFirstBoot, mOnlyCore, new PhoneWindowManager());
- mActivityManagerService.setWindowManager(wm);
- //...
- }
- public void setSystemProcess() {
- try {
- ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
- DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
- }
- }
其中第二步setSystemProcess方法中,会注册AMS到ServiceManager中,这样后续如果需要用到AMS的时候就可以通过ServiceManager进行获取,下面马上就要讲到。
启动就说这么多,都是比较枯燥的内容,所以也没有深入下去,有个印象就行,以后如果需要用到相关知识就知道去哪里找了。
从启动流程看AMS工作内容
为了了解AMS的具体工作,我们就从Activity的启动过程看起。
上文app启动流程中说过,startActivityForResult方法会转到mInstrumentation.execStartActivity方法:
- //mInstrumentation.execStartActivity
- int result = ActivityManager.getService()
- .startActivity(whoThread, who.getBasePackageName(), intent,
- intent.resolveTypeIfNeeded(who.getContentResolver()),
- token, target != null ? target.mEmbeddedID : null,
- requestCode, 0, null, options);
- checkStartActivityResult(result, intent);
- public static IActivityManager getService() {
- return IActivityManagerSingleton.get();
- }
- private static final Singleton<IActivityManager> IActivityManagerSingleton =
- new Singleton<IActivityManager>() {
- @Override
- protected IActivityManager create() {
- final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
- final IActivityManager am = IActivityManager.Stub.asInterface(b);
- return am;
- }
- };
可以看到,最终要拿到AMS的IBinder类型引用,这里的ServiceManager.getService(Context.ACTIVITY_SERVICE)是不是有点熟悉,没错,就是刚才专门调用了setSystemProcess方法对AMS进行了注册在ServiceManager中。然后我们要使用相关服务的方法的时候,就通过Servermanager拿到对应服务的引用。
这里也就是拿到了IActivityManager对象,IActivityManager其实就是AMS在当前进程的代理,这里的逻辑就是通过AIDL做了一个进程间的通信。因为这些服务,包括我们今天说的AMS都是在SystemServer进程中的,而我们实际用到的时候是在我们自己的应用进程中,所以就涉及到进程间通信了,这里是用的Binder机制进行通信。
Binder,ServiceManager,这是Binder通信一整套流程,不光是AMS,包括其他的WMS等服务基本上都是通过Binder机制进行进程间通信的,具体内容可以期待下后面说到的Binder章节。
接着看启动流程,通过Binder调用到了AMS的startActivity方法,然后会调用到ActivityStarter的startActivity方法,在这个方法中,我们发现一个新的类:
- //ActivityStarter.java
- private int startActivity(...){
- ActivityRecord r = new ActivityRecord(mService, callerApp, callingPid, callingUid,
- callingPackage, intent, resolvedType, aInfo, mService.getGlobalConfiguration(),
- resultRecord, resultWho, requestCode, componentSpecified, voiceSession != null,
- mSupervisor, checkedOptions, sourceRecord);
- if (outActivity != null) {
- outActivity[0] = r;
- }
- //...
- return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags,
- true /* doResume */, checkedOptions, inTask, outActivity);
- }
ActivityRecord
这个类翻译过来是Activity的记录,所以猜测是和Activity有关,我们点进去看看它里面包含了什么:
- final ActivityManagerService service; // owner
- final IApplicationToken.Stub appToken; // window manager token
- final ActivityInfo info; // all about me
- ApplicationInfo appInfo; // information about activity's app
- final int userId; // Which user is this running for?
- final String packageName; // the package implementing intent's component
- final String processName; // process where this component wants to run
- final String taskAffinity; // as per ActivityInfo.taskAffinity
- private int icon; // resource identifier of activity's icon.
- private int logo; // resource identifier of activity's logo.
- private int theme; // resource identifier of activity's theme.
- int launchMode; // the launch mode activity attribute.
我保留了一些比较常用的属性,大家应该都看得出来是什么了吧,比如当前Activity的主题——theme,当前Activity的token——apptoken,当前Activity的包名——packageName。
所以这个ActivityRecord其实就是保存记录了Activity的所有信息。
接着看流程,后续会执行到startActivityUnchecked方法,这个方法中,我们又可以看到一个新的类——TaskRecord.
TaskRecord
- private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
- IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
- int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
- ActivityRecord[] outActivity) {
- if (mStartActivity.resultTo == null && mInTask == null && !mAddingToTask
- && (mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0) {
- newTask = true;
- result = setTaskFromReuseOrCreateNewTask(taskToAffiliate, topStack);
- } else if (mSourceRecord != null) {
- result = setTaskFromSourceRecord();
- } else if (mInTask != null) {
- result = setTaskFromInTask();
- } else {
- // This not being started from an existing activity, and not part of a new task...
- // just put it in the top task, though these days this case should never happen.
- setTaskToCurrentTopOrCreateNewTask();
- }
- }
- // 新建一个任务栈
- private void setTaskToCurrentTopOrCreateNewTask() {
- //...
- final ActivityRecord prev = mTargetStack.getTopActivity();
- final TaskRecord task = (prev != null) ? prev.getTask() : mTargetStack.createTaskRecord(
- mSupervisor.getNextTaskIdForUserLocked(mStartActivity.userId), mStartActivity.info,
- mIntent, null, null, true, mStartActivity, mSourceRecord, mOptions);
- addOrReparentStartingActivity(task, "setTaskToCurrentTopOrCreateNewTask");
- mTargetStack.positionChildWindowContainerAtTop(task);
- }
- //添加Ac到栈顶
- private void addOrReparentStartingActivity(TaskRecord parent, String reason) {
- if (mStartActivity.getTask() == null || mStartActivity.getTask() == parent) {
- parent.addActivityToTop(mStartActivity);
- } else {
- mStartActivity.reparent(parent, parent.mActivities.size() /* top */, reason);
- }
- }
从代码中可知,当我们启动的Activity需要一个新的任务栈的时候(比如启动模式为FLAG_ACTIVITY_NEW_TASK),我们会走到setTaskToCurrentTopOrCreateNewTask方法中,新建一个TaskRecord类,并且把当前的Activity通过addActivityToTop方法添加到栈顶。
所以这个TaskRecord类就是一个任务栈类了,它的作用就是维护栈内的所有Activity,进去看看这个类有哪些变量:
- final int taskId; // Unique identifier for this task.
- /** List of all activities in the task arranged in history order */
- final ArrayList<ActivityRecord> mActivities;
- /** Current stack. Setter must always be used to update the value. */
- private ActivityStack mStack;
这里截取了一些,可以发现有任务id——taskId,任务栈的所有ActivityRecord——mActivities,以及这个还不知道是什么的但是我知道是用来管理所有Activity和任务栈的大管家——ActivityStack。
ActivityStack
启动流程再往后面走,就会走到的ActivityStackSupervisor的resumeFocusedStackTopActivityLocked方法:
- //ActivityStackSupervisor.java
- /** The stack containing the launcher app. Assumed to always be attached to
- * Display.DEFAULT_DISPLAY. */
- ActivityStack mHomeStack;
- /** The stack currently receiving input or launching the next activity. */
- ActivityStack mFocusedStack;
- /** If this is the same as mFocusedStack then the activity on the top of the focused stack has
- * been resumed. If stacks are changing position this will hold the old stack until the new
- * stack becomes resumed after which it will be set to mFocusedStack. */
- private ActivityStack mLastFocusedStack;
- public ActivityStackSupervisor(ActivityManagerService service, Looper looper) {
- mService = service;
- mLooper = looper;
- mHandler = new ActivityStackSupervisorHandler(looper);
- }
- boolean resumeFocusedStackTopActivityLocked(
- ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
- if (targetStack != null && isFocusedStack(targetStack)) {
- return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
- }
- final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
- if (r == null || !r.isState(RESUMED)) {
- mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
- } else if (r.isState(RESUMED)) {
- // Kick off any lingering app transitions form the MoveTaskToFront operation.
- mFocusedStack.executeAppTransition(targetOptions);
- }
- return false;
- }
ActivityStackSupervisor是一个管理ActivityStack的类,在AMS的构造方法中被创建,这个类中可以看到有一些任务栈,比如mHomeStack——包含了Launcher APP的Activity。
然后再看看ActivityStack这个大管家家里存储了什么好东西:
- enum ActivityState {
- INITIALIZING,
- RESUMED,
- PAUSING,
- PAUSED,
- STOPPING,
- STOPPED,
- FINISHING,
- DESTROYING,
- DESTROYED
- }
- private final ArrayList<TaskRecord> mTaskHistory = new ArrayList<>();
- final ArrayList<ActivityRecord> mLRUActivities = new ArrayList<>();
- ActivityRecord mPausingActivity = null;
- ActivityRecord mLastPausedActivity = null;
可以看到,在ActivityStack中:
- 有一个枚举ActivityState,存储了Activity的所有状态。
- 有一些TaskRecord和ActivityRecord的列表,比如mTaskHistory——没有被销毁的任务栈列表,mLRUActivities——通过LRU计算的列表头目是最近最少使用的Activity的ActivityRecord列表。
- 还有一些特殊状态的Activity对应的ActivityRecord,比如正在暂停的Activity,上一个暂停过的Activity。
最后,启动流程会走到AMS的startProcessLocked方法,然后跟Zygote进程通信,fork进程。后续就不说了。
总结
到此,AMS中重要的三个组件我们都接触过了,分别是:
- 管理Activity所有信息的ActivityRecord。
- 管理一个或者多个ActivityRecord的任务栈TaskRecord.
- 管理一个或者多个任务栈的管理者ActivityStack。
再来画个图总结下:
其实AMS里面的逻辑还有很多很多,不仅是Activity,还有其他三大组件的一些启动调度流程都是通过AMS完成的,还有Activity任务栈相关的内容(包括taskAffinity、allowTaskReparenting),后续具体涉及到的时候会再细谈。
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