Android-AMS（一）-启动流程分析

AMS是Android中最核心的服务，主要负责系统中四大组件的启动、切换、调度及应用进程的管理和调度等工作，其职责与操作系统中的进程管理和调度模块相类似，因此它在Android中非常重要。

客户端使用ActivityManager类。由于AMS是系统核心服务，很多API不能开放供客户端使用，所以设计者没有让ActivityManager直接加入AMS家族。在ActivityManager类内部通过调用AMN的getDefault函数得到一个ActivityManagerProxy对象，通过它可与AMS通信。

源码分析流程使用Android O 的源码即Android8.0

>AMS启动流程源码分析

　　1.AMS由SystemServer的ServerThread线程创建，代码如下：

　　　　由以上代码分析可得：

　　　　　　AMS的创建是通过ActivityManagerService.java里面的Lifecycle类创建出来的。该LifeCycle的代码如下：

这个其实很好理解啦，就相当于AMS的生命周期。在后面的源码分析中我们会经常看到这个类，没什么好说的，就相当于一个服务的生命周期，从创建到销毁的整个过程。

　　　　　　我们去看一下AMS的构造方法里面有些什么东西，代码如下：

  1     public ActivityManagerService(Context systemContext) {
  2         LockGuard.installLock(this, LockGuard.INDEX_ACTIVITY);
  3         mInjector = new Injector();
  4         mContext = systemContext;
  5 
  6         mFactoryTest = FactoryTest.getMode();
  7         mSystemThread = ActivityThread.currentActivityThread();
  8         mUiContext = mSystemThread.getSystemUiContext();
  9 
 10         Slog.i(TAG, "Memory class: " + ActivityManager.staticGetMemoryClass());
 11 
 12         mPermissionReviewRequired = mContext.getResources().getBoolean(
 13                 com.android.internal.R.bool.config_permissionReviewRequired);
 14 
 15         mHandlerThread = new ServiceThread(TAG,
 16                 THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
 17         mHandlerThread.start();
 18         mHandler = new MainHandler(mHandlerThread.getLooper());
 19         mUiHandler = mInjector.getUiHandler(this);
 20 
 21         mConstants = new ActivityManagerConstants(this, mHandler);
 22 
 23         /* static; one-time init here */
 24         if (sKillHandler == null) {
 25             sKillThread = new ServiceThread(TAG + ":kill",
 26                     THREAD_PRIORITY_BACKGROUND, true /* allowIo */);
 27             sKillThread.start();
 28             sKillHandler = new KillHandler(sKillThread.getLooper());
 29         }
 30 
 31         mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
 32                 "foreground", BROADCAST_FG_TIMEOUT, false);
 33         mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
 34                 "background", BROADCAST_BG_TIMEOUT, true);
 35         mBroadcastQueues[0] = mFgBroadcastQueue;
 36         mBroadcastQueues[1] = mBgBroadcastQueue;
 37 
 38         mServices = new ActiveServices(this);
 39         mProviderMap = new ProviderMap(this);
 40         mAppErrors = new AppErrors(mUiContext, this);
 41 
 42         // TODO: Move creation of battery stats service outside of activity manager service.
 43         File dataDir = Environment.getDataDirectory();
 44         File systemDir = new File(dataDir, "system");
 45         systemDir.mkdirs();
 46         mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);
 47         mBatteryStatsService.getActiveStatistics().readLocked();
 48         mBatteryStatsService.scheduleWriteToDisk();
 49         mOnBattery = DEBUG_POWER ? true
 50                 : mBatteryStatsService.getActiveStatistics().getIsOnBattery();
 51         mBatteryStatsService.getActiveStatistics().setCallback(this);
 52 
 53         mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));
 54 
 55         mAppOpsService = mInjector.getAppOpsService(new File(systemDir, "appops.xml"), mHandler);
 56         mAppOpsService.startWatchingMode(AppOpsManager.OP_RUN_IN_BACKGROUND, null,
 57                 new IAppOpsCallback.Stub() {
 58                     @Override public void opChanged(int op, int uid, String packageName) {
 59                         if (op == AppOpsManager.OP_RUN_IN_BACKGROUND && packageName != null) {
 60                             if (mAppOpsService.checkOperation(op, uid, packageName)
 61                                     != AppOpsManager.MODE_ALLOWED) {
 62                                 runInBackgroundDisabled(uid);
 63                             }
 64                         }
 65                     }
 66                 });
 67 
 68         mGrantFile = new AtomicFile(new File(systemDir, "urigrants.xml"));
 69 
 70         mUserController = new UserController(this);
 71 
 72         mVrController = new VrController(this);
 73 
 74         GL_ES_VERSION = SystemProperties.getInt("ro.opengles.version",
 75             ConfigurationInfo.GL_ES_VERSION_UNDEFINED);
 76 
 77         if (SystemProperties.getInt("sys.use_fifo_ui", 0) != 0) {
 78             mUseFifoUiScheduling = true;
 79         }
 80 
 81         mTrackingAssociations = "1".equals(SystemProperties.get("debug.track-associations"));
 82         mTempConfig.setToDefaults();
 83         mTempConfig.setLocales(LocaleList.getDefault());
 84         mConfigurationSeq = mTempConfig.seq = 1;
 85         mStackSupervisor = createStackSupervisor();
 86         mStackSupervisor.onConfigurationChanged(mTempConfig);
 87         mKeyguardController = mStackSupervisor.mKeyguardController;
 88         mCompatModePackages = new CompatModePackages(this, systemDir, mHandler);
 89         mIntentFirewall = new IntentFirewall(new IntentFirewallInterface(), mHandler);
 90         mTaskChangeNotificationController =
 91                 new TaskChangeNotificationController(this, mStackSupervisor, mHandler);
 92         mActivityStarter = new ActivityStarter(this, mStackSupervisor);
 93         mRecentTasks = new RecentTasks(this, mStackSupervisor);
 94 
 95         mProcessCpuThread = new Thread("CpuTracker") {
 96             @Override
 97             public void run() {
 98                 synchronized (mProcessCpuTracker) {
 99                     mProcessCpuInitLatch.countDown();
100                     mProcessCpuTracker.init();
101                 }
102                 while (true) {
103                     try {
104                         try {
105                             synchronized(this) {
106                                 final long now = SystemClock.uptimeMillis();
107                                 long nextCpuDelay = (mLastCpuTime.get()+MONITOR_CPU_MAX_TIME)-now;
108                                 long nextWriteDelay = (mLastWriteTime+BATTERY_STATS_TIME)-now;
109                                 //Slog.i(TAG, "Cpu delay=" + nextCpuDelay
110                                 //        + ", write delay=" + nextWriteDelay);
111                                 if (nextWriteDelay < nextCpuDelay) {
112                                     nextCpuDelay = nextWriteDelay;
113                                 }
114                                 if (nextCpuDelay > 0) {
115                                     mProcessCpuMutexFree.set(true);
116                                     this.wait(nextCpuDelay);
117                                 }
118                             }
119                         } catch (InterruptedException e) {
120                         }
121                         updateCpuStatsNow();
122                     } catch (Exception e) {
123                         Slog.e(TAG, "Unexpected exception collecting process stats", e);
124                     }
125                 }
126             }
127         };
128 
129         Watchdog.getInstance().addMonitor(this);
130         Watchdog.getInstance().addThread(mHandler);
131     }