ActivityManagerService架构剖析开篇
ActivityManagerService是Android提供了管理Activity运行状态的系统进程,其实大家别被名字迷惑了,AMS(接下来都称ActivityManagerService为AMS)其实也兼任管理其他组件运行状态。
一、AMS概述
1.1 AMS启动流程
init进程是Android系统中的初始化进程,init生成Zygote进程,Android中大多数应用进程和系统进程都是通过Zygote进程生成的。
AMS触发流程.jpg
AMS这种系统级别的服务,一般都是在启动的时候触发,上面的流程详细地阐述了AMS的代码执行流程。由于本文并不是介绍Zygote的,所以这儿不作详细描述,可以参考一下我其他详述Zygote的文章。
AMS启动时的代码:
SystemServer.javaprivate void startBootstrapServices() {//...... mActivityManagerService = mSystemServiceManager.startService( ActivityManagerService.Lifecycle.class).getService(); mActivityManagerService.setSystemServiceManager(mSystemServiceManager); mActivityManagerService.setInstaller(installer);//...... mActivityManagerService.setSystemProcess();//......}
其中获取AMS的地方有一点改动,去掉了AMS中的main(...)方法,将其中的工作移到AMS构造函数中。
ActivityManagerService.javapublic 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 onCleanupUser(int userId) { mService.mBatteryStatsService.onCleanupUser(userId); } public ActivityManagerService getService() { return mService; } }
1.2 AMS初始化工作
从上面AMS启动流程来看,AMS在在setSystemProcess()中注册的,注册的函数就是ServiceManager. addService(Context.ACTIVITY_SERVICE, this, true);从代码中看出来,AMS是一个实名的binder server,并且在AMS还注册了很多其他的服务,例如meminfo(这是内存使用情况的server)、cpuinfo(这是CPU使用情况的server)等等,这些服务在AMS中注册启用,说明这些服务会和AMS有很多交互。
ActivityManagerService.javapublic void setSystemProcess() {//...... ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true); ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats); ServiceManager.addService("meminfo", new MemBinder(this)); ServiceManager.addService("gfxinfo", new GraphicsBinder(this)); ServiceManager.addService("dbinfo", new DbBinder(this)); if (MONITOR_CPU_USAGE) { ServiceManager.addService("cpuinfo", new CpuBinder(this)); } ServiceManager.addService("permission", new PermissionController(this)); ServiceManager.addService("processinfo", new ProcessInfoService(this));//......}
我们查看一下AMS的构造做了什么事情,从代码中分段讲解AMS构造中要做的事情。
ActivityManagerService.javapublic ActivityManagerService(Context systemContext) {//......//step1: mSystemThread = ActivityThread.currentActivityThread(); mUiContext = mSystemThread.getSystemUiContext(); mPermissionReviewRequired = mContext.getResources().getBoolean( com.android.internal.R.bool.config_permissionReviewRequired); mHandlerThread = new ServiceThread(TAG, THREAD_PRIORITY_FOREGROUND, false /*allowIo*/); mHandlerThread.start(); mHandler = new MainHandler(mHandlerThread.getLooper()); mUiHandler = mInjector.getUiHandler(this); mConstants = new ActivityManagerConstants(this, mHandler);//......//step2: mFgBroadcastQueue = new BroadcastQueue(this, mHandler, "foreground", BROADCAST_FG_TIMEOUT, false); mBgBroadcastQueue = new BroadcastQueue(this, mHandler, "background", BROADCAST_BG_TIMEOUT, true); mBroadcastQueues[0] = mFgBroadcastQueue; mBroadcastQueues[1] = mBgBroadcastQueue;//step3: mServices = new ActiveServices(this); mProviderMap = new ProviderMap(this); mAppErrors = new AppErrors(mUiContext, this);//step4: // TODO: Move creation of battery stats service outside of activity manager service. File dataDir = Environment.getDataDirectory(); File systemDir = new File(dataDir, "system"); systemDir.mkdirs(); mBatteryStatsService = new BatteryStatsService(systemContext, systemDir, mHandler); mBatteryStatsService.getActiveStatistics().readLocked(); mBatteryStatsService.scheduleWriteToDisk(); mOnBattery = DEBUG_POWER ? true : mBatteryStatsService.getActiveStatistics().getIsOnBattery(); mBatteryStatsService.getActiveStatistics().setCallback(this); mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats")); mAppOpsService = mInjector.getAppOpsService(new File(systemDir, "appops.xml"), mHandler); mAppOpsService.startWatchingMode(AppOpsManager.OP_RUN_IN_BACKGROUND, null, new IAppOpsCallback.Stub() { @Override public void opChanged(int op, int uid, String packageName) { if (op == AppOpsManager.OP_RUN_IN_BACKGROUND && packageName != null) { if (mAppOpsService.checkOperation(op, uid, packageName) != AppOpsManager.MODE_ALLOWED) { runInBackgroundDisabled(uid); } } } }); mGrantFile = new AtomicFile(new File(systemDir, "urigrants.xml")); mUserController = new UserController(this); mVrController = new VrController(this); GL_ES_VERSION = SystemProperties.getInt("ro.opengles.version", ConfigurationInfo.GL_ES_VERSION_UNDEFINED); if (SystemProperties.getInt("sys.use_fifo_ui", 0) != 0) { mUseFifoUiScheduling = true; }//......//step5: mStackSupervisor = createStackSupervisor(); mStackSupervisor.onConfigurationChanged(mTempConfig); mKeyguardController = mStackSupervisor.mKeyguardController; mCompatModePackages = new CompatModePackages(this, systemDir, mHandler); mIntentFirewall = new IntentFirewall(new IntentFirewallInterface(), mHandler); mTaskChangeNotificationController = new TaskChangeNotificationController(this, mStackSupervisor, mHandler); mActivityStarter = new ActivityStarter(this, mStackSupervisor); mRecentTasks = new RecentTasks(this, mStackSupervisor);//step6: mProcessCpuThread = new Thread("CpuTracker") { @Override public void run() { synchronized (mProcessCpuTracker) { mProcessCpuInitLatch.countDown(); mProcessCpuTracker.init(); } while (true) { try { try { synchronized(this) { final long now = SystemClock.uptimeMillis(); long nextCpuDelay = (mLastCpuTime.get()+MONITOR_CPU_MAX_TIME)-now; long nextWriteDelay = (mLastWriteTime+BATTERY_STATS_TIME)-now; //Slog.i(TAG, "Cpu delay=" + nextCpuDelay // + ", write delay=" + nextWriteDelay); if (nextWriteDelay < nextCpuDelay) { nextCpuDelay = nextWriteDelay; } if (nextCpuDelay > 0) { mProcessCpuMutexFree.set(true); this.wait(nextCpuDelay); } } } catch (InterruptedException e) { } updateCpuStatsNow(); } catch (Exception e) { Slog.e(TAG, "Unexpected exception collecting process stats", e); } } } }; mHiddenApiBlacklist = new HiddenApiBlacklist(mHandler, mContext); Watchdog.getInstance().addMonitor(this); Watchdog.getInstance().addThread(mHandler); }
通过分析上面的代码,将AMS的构造分为6个重要的步骤:
1.初始化构造AMS要用到的一些context和handler,例如mUiContext和mUiHandler配合使用,用于处理和UI显示相关的工作,mHandler是AMS中定义的用于分发AMS相关信息的处理器。
2.定义了容纳前台和后台的广播队列,这也说明了AMS不仅仅关注Activity,也负责其他组件状态的管理。
3.管理Service和Provider的对象数组。
4.初始化system下面需要的一系列文件目录。例如权限文件、进程状态信息文件等等。
5.这儿比较重要了,几个重要的变量需要关注一下,ActivityStackSupervisor(管理ActivityStack的重要类,这里面记录着activity状态信息,是AMS中的核心类), ActivityStarter(这是activity启动的处理类,这里管理者activity启动中用到的intent信息和flag标识,也和stack和task有重要的联系,下面会重点阐述)。
6.启动一个线程专门跟进cpu当前状态信息,AMS对当前cpu状态了如指掌,可以更加高效的安排其他工作。
二、Activity状态
2.1 Activity生命周期
Android入门必学的就是Android的四大组件,我们开发第一个app的时候,都会用到Activity,对于Activity的生命周期,大家应该已经烂熟于心了。下面是Activity生命周期状态图。
Activity生命周期.jpg
在这里我就不展开对生命周期的讨论了,这方面的文章还是很多的,我说一个比较重要的知识点吧,也是比较容易错的一个点,Android面试的时候,都会问这样一个问题:什么时候Activity对用户可见?这个问题相信大家都遇到过,之前看过的一些书都说是在执行onResume()的时候表明当前Activity已经可见了,这个回答可以说对,也可以说不对。因为执行onResume()的时候Activity确实可见了,但是只是这样回答不能让人满意,说明没有深入思考,也没有仔细查看源码。下面带大家看一下这一部分的源码:
ActivityThread.javafinal void handleResumeActivity(IBinder token, boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {//...... // TODO Push resumeArgs into the activity for consideration r = performResumeActivity(token, clearHide, reason); if (r != null) {//...... boolean willBeVisible = !a.mStartedActivity; if (!willBeVisible) { try { willBeVisible = ActivityManager.getService().willActivityBeVisible( a.getActivityToken()); } catch (RemoteException e) { throw e.rethrowFromSystemServer(); } } if (r.window == null && !a.mFinished && willBeVisible) { r.window = r.activity.getWindow(); View decor = r.window.getDecorView(); decor.setVisibility(View.INVISIBLE); ViewManager wm = a.getWindowManager(); WindowManager.LayoutParams l = r.window.getAttributes(); a.mDecor = decor; l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION; l.softInputMode |= forwardBit;//...... if (a.mVisibleFromClient) { if (!a.mWindowAdded) { a.mWindowAdded = true; wm.addView(decor, l); } //...... } // If the window has already been added, but during resume // we started another activity, then don't yet make the // window visible. } else if (!willBeVisible) { if (localLOGV) Slog.v( TAG, "Launch " + r + " mStartedActivity set"); r.hideForNow = true; } // Get rid of anything left hanging around. cleanUpPendingRemoveWindows(r, false /* force */); // The window is now visible if it has been added, we are not // simply finishing, and we are not starting another activity. if (!r.activity.mFinished && willBeVisible && r.activity.mDecor != null && !r.hideForNow) {//...... if (r.activity.mVisibleFromClient) { r.activity.makeVisible(); } }//...... } //...... }
此函数是handleResumeActivity(...),从字面上看应该是和onResume相关,在此函数中有执行activity.makeVisible(),这个makeVisible就是当前Activity可见的执行函数,所以严格来讲,不能说onResume是让Activity可见的,这点关系要搞清楚。下面Activity处理流程中详细画出了当前的Activity状态的时序图,里面也写明了Activity可见的调用时机。
Android生命周期都是在UI线程中运行的,所以在这里面执行的代码都不能有过分耗时的情况,否则会发生ANR等问题,这个需要平时开发的时候养成良好的习惯。Android的生命周期是系统给开发者提供的一个体现当前Activity所处状态的外在体现,掌握这些生命周期,不能仅仅停留在表面的认识上,还应该知道深层的调用规律和调用逻辑。
2.2 Activity状态管理
Android是如何管理Activity状态的,我们平时在Android开发中用到的intent flags taskAffinity launchMode是如何管理的,一个Task包含一个或者多个Activity,一个Stack包含一个或者多个Task,这儿引入ActivityStack,还有ActivityStackSupervisor负责管理所有的Stack。那么Activity是如何创建并且如何管理的?
2.2.1 ActivityStack创建
ActivityStack创建过程.jpg从ActivityStack创建的过程中也能看出来,ActivityStackSupervisor是管理ActivityStack的重要类,操作ActivityStack,都通过ActivityStackSupervisor衍生一个接口来执行。
ActivityStackSupervisor.javavoid setWindowManager(WindowManagerService wm) { synchronized (mService) {//...... mHomeStack = mFocusedStack = mLastFocusedStack = getStack(HOME_STACK_ID, CREATE_IF_NEEDED, ON_TOP);//...... } } protected T getStack(int stackId, boolean createStaticStackIfNeeded, boolean createOnTop) { final ActivityStack stack = mStacks.get(stackId); if (stack != null) { return (T) stack; } if (!createStaticStackIfNeeded || !StackId.isStaticStack(stackId)) { return null; } if (stackId == DOCKED_STACK_ID) { // Make sure recents stack exist when creating a dock stack as it normally need to be on // the other side of the docked stack and we make visibility decisions based on that. getStack(RECENTS_STACK_ID, CREATE_IF_NEEDED, createOnTop); } return (T) createStackOnDisplay(stackId, DEFAULT_DISPLAY, createOnTop); } ActivityStack createStackOnDisplay(int stackId, int displayId, boolean onTop) { final ActivityDisplay activityDisplay = getActivityDisplayOrCreateLocked(displayId); if (activityDisplay == null) { return null; } return createStack(stackId, activityDisplay, onTop); } ActivityStack createStack(int stackId, ActivityDisplay display, boolean onTop) { switch (stackId) { case PINNED_STACK_ID: return new PinnedActivityStack(display, stackId, this, mRecentTasks, onTop); default: return new ActivityStack(display, stackId, this, mRecentTasks, onTop); } }
初始化创建了mHomeStack(包含launcher app)、mFocusStack(接收当前即将启动的Activity)、mLastFocusedStack(接收上次启动的Activity),从代码中更好理解这些概念,下面ActivityStack分析会详细讨论这3个stack的调用时机。
2.2.1 ActivityStack概述
ActivityStack详细分析会在下一张讲解。本文只是简单介绍一下ActivityStack中常用的变量,这些变量对理解ActivityStack的功能有很大的帮助。
1.定义ActivityState
ActivityStack.javaenum ActivityState { INITIALIZING, RESUMED, PAUSING, PAUSED, STOPPING, STOPPED, FINISHING, DESTROYING, DESTROYED }
2.特殊状态下的Activity
ActivityStack ActivityRecord mPausingActivity = null; ActivityRecord mLastPausedActivity = null; ActivityRecord mLastNoHistoryActivity = null; ActivityRecord mResumedActivity = null;
mPausingActivity表示正在被暂停的Activity
mLastPausedActivity 表示上一个被暂停的Activity
mLastNoHistoryActivity 表示上一个设置为FLAG_ACTIVITY_NO_HISTORY的Activity
mResumedActivity 表示当前处于恢复状态的Activity
3.全局的ArrayList
ActivityStack.java private final ArrayList mTaskHistory = new ArrayList<>(); final ArrayList mLRUActivities = new ArrayList<>(); final ArrayList mNoAnimActivities = new ArrayList<>();
mTaskHistory 记录所有的Activity信息
mLRUActivities 按照最近最少使用排序的Activity集合
mNoAnimActivities 不考虑状态迁移动画的Activity集合
三、Activity处理流程
3.1 startActivity流程
启动一个Activity之后经历的流程如图所示,这儿写明了回调各个流程的时机,其中包含这对Activity状态的处理,这一点非常重要,Android系统处理的Activity很多,我们准确指示当前Activity的状态,可以保证Activity调用的正确性。由于onPause()触发条件比较多,这边没有列出onPause()的回调流程,感兴趣的同学可以自己查看一下源码,学习一下具体的流程,但是Activity生命周期的核心要点都在onCreate() onStart() onResume()上面,其他的生命周期其实就是对Activity状态的维护。
Activity处理流程.jpg
应用程序的入口在什么地方?这也是面试中经常问到的问题,别告诉我你想回答是Activity.onCreate(...),那显然大错特错,所谓应用程序的入口,就是当前的应用程序所在的进程是什么时候被启动的,这才是关键。解答这个问题,不看源码,很难问答,如果只是对Activity生命周期有一个表象的认识,显然不太够。这里列出关键的地方,抛砖引玉。
ActivityStackSupervisor.javavoid startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) { // Is this activity's application already running? ProcessRecord app = mService.getProcessRecordLocked(r.processName, r.info.applicationInfo.uid, true); r.getStack().setLaunchTime(r);//step1: if (app != null && app.thread != null) { try { if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0 || !"android".equals(r.info.packageName)) { // Don't add this if it is a platform component that is marked // to run in multiple processes, because this is actually // part of the framework so doesn't make sense to track as a // separate apk in the process. app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode, mService.mProcessStats); } realStartActivityLocked(r, app, 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. }//step2: mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0, "activity", r.intent.getComponent(), false, false, true); }
上面标注了step1和step2,从step1的判断来看if (app != null && app.thread != null),说明当前的Activity所在的进程存在的话,执行realStartActivityLocked(...),那么step2执行的条件显然就是当前Activity所在的进程不存在的情况了。继续看下去。
Activity启动入口.jpg
很显然,ActivityThread->main(...)才是应用程序真正的启动入口。仔细阅读源码能帮助我们什么?能帮助我们透过现象看本质。
更多相关文章
- Android(安卓)Gems — AMS的Service生命周期管理
- Android(安卓)待机流程解析
- Android(安卓)Fragment使用小结
- android沉浸式状态栏的问题解决
- Android(安卓)Media Framework(3): Stagefright框架流程解读
- Android学习笔记(五) Acticity跳转并传值
- Android(安卓)View 事件分发机制流程
- android生命周期测试
- Android(安卓)CheckBox使用所遇到的坑