AMS

 1    以桌面启动一个应用Activity为例，onClick事件后，会调用startActivityForResult(Intent, int)
      public void startActivityForResult(Intent intent, int requestCode, Bundle options) {
 2         if (mParent == null) {
                //Activity启动执行交由Instrumentation对象去处理
 3             Instrumentation.ActivityResult ar =
 4                 mInstrumentation.execStartActivity(
                   //mMainThread 在attach方法中被设置，当ActivityThread PerformLauchActivity，调用attach把ActivityThread.this传送过来
               //mMainThread.getApplicationThread()它是一个进程通信服务端存根对象，提供了很多操作ActivityThread的方法，它继承了ApplicationThreadNative       
 5                     this, mMainThread.getApplicationThread(), mToken, this,
 6                     intent, requestCode, options);
 7             if (ar != null) {
 8                 mMainThread.sendActivityResult(
 9                     mToken, mEmbeddedID, requestCode, ar.getResultCode(),
10                     ar.getResultData());
11             }
12             if (requestCode >= 0) {
13                 // If this start is requesting a result, we can avoid making
14                 // the activity visible until the result is received.  Setting
15                 // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
16                 // activity hidden during this time, to avoid flickering.
17                 // This can only be done when a result is requested because
18                 // that guarantees we will get information back when the
19                 // activity is finished, no matter what happens to it.
20                 mStartedActivity = true;
21             }
22 
23             final View decor = mWindow != null ? mWindow.peekDecorView() : null;
24             if (decor != null) {
25                 decor.cancelPendingInputEvents();
26             }
27             // TODO Consider clearing/flushing other event sources and events for child windows.
28         } else {
29             if (options != null) {
30                 mParent.startActivityFromChild(this, intent, requestCode, options);
31             } else {
32                 // Note we want to go through this method for compatibility with
33                 // existing applications that may have overridden it.
34                 mParent.startActivityFromChild(this, intent, requestCode);
35             }
36         }
37     }

//①调用main函数，得到一个Context对象

context =ActivityManagerService.main(factoryTest);

 

//②setSystemProcess：这样SystemServer进程可加到AMS中，并被它管理

ActivityManagerService.setSystemProcess();

 

//③installSystemProviders：将SettingsProvider放到SystemServer进程中来运行

ActivityManagerService.installSystemProviders();

 

//④在内部保存WindowManagerService（以后简称WMS）

ActivityManagerService.self().setWindowManager(wm);

 

//⑤和WMS交互，弹出“启动进度“对话框

ActivityManagerNative.getDefault().showBootMessage(

             context.getResources().getText(

               //该字符串中文为：“正在启动应用程序”

               com.android.internal.R.string.android_upgrading_starting_apps),

              false);

 

//⑥AMS是系统的核心，只有它准备好后，才能调用其他服务的systemReady

//注意，有少量服务在AMS systemReady之前就绪，它们不影响此处的分析

ActivityManagerService.self().systemReady(newRunnable() {

    publicvoid run() {

   startSystemUi(contextF);//启动systemUi。如此，状态栏就准备好了

    if(batteryF != null) batteryF.systemReady();

    if(networkManagementF != null) networkManagementF.systemReady();

    ......

    Watchdog.getInstance().start();//启动Watchdog

    ......//调用其他服务的systemReady函数

}

 AThread thr = new AThread();//①创建一个AThread线程对象
    thr.start();
    ......//等待thr创建成功
    ActivityManagerService m = thr.mService;
    mSelf =m;
    //②调用ActivityThread的systemMain函数
    ActivityThread at = ActivityThread.systemMain();
    mSystemThread= at;
 
    //③得到一个Context对象，注意调用的函数名为getSystemContext，何为System Context
    Context context = at.getSystemContext();
    context.setTheme(android.R.style.Theme_Holo);
    m.mContext= context;
    m.mFactoryTest= factoryTest;
 
    //ActivtyStack是AMS中用来管理Activity的启动和调度的核心类，以后再分析它
    m.mMainStack = new ActivityStack(m, context,true);
    //调用BSS的publish函数，我们在第5章的BSS知识中介绍过了
    m.mBatteryStatsService.publish(context);
    //另外一个service：UsageStatsService。后续再分析该服务
    m.mUsageStatsService.publish(context);
    synchronized (thr) {
           thr.mReady = true;
           thr.notifyAll();//通知thr线程，本线程工作完成
     }
 
    //④调用AMS的startRunning函数
    m.startRunning(null, null, null, null);
       
   return context;
}

static class AThread extends Thread {//AThread从Thread类派生
   ActivityManagerServicemService;
   booleanmReady = false;
   publicAThread() {
     super("ActivityManager");//线程名就叫“ActivityManager”
   }
   publicvoid run() {
     Looper.prepare();//看来，AThread线程将支持消息循环及处理功能
     android.os.Process.setThreadPriority(//设置线程优先级
                   android.os.Process.THREAD_PRIORITY_FOREGROUND);
     android.os.Process.setCanSelfBackground(false);
      //创建AMS对象
     ActivityManagerService m = new ActivityManagerService();
     synchronized (this) {
           mService= m;//赋值AThread内部成员变量mService，指向AMS
          notifyAll();  //通知main函数所在线程
      }
     synchronized (this) {
        while (!mReady) {
           try{
                 wait();//等待main函数所在线程的notifyAll
               }......
           }
       }......
    Looper.loop();//进入消息循环
 }
 }

private ActivityManagerService() {
    FiledataDir = Environment.getDataDirectory();//指向/data/目录
    FilesystemDir = new File(dataDir, "system");//指向/data/system/目录
   systemDir.mkdirs();//创建/data/system/目录
 
    //创建BatteryStatsService（以后简称BSS）和UsageStatsService（以后简称USS）
   //我们在分析PowerManageService时已经见过BSS了
   mBatteryStatsService = new BatteryStatsService(new File(
               systemDir, "batterystats.bin").toString());
   mBatteryStatsService.getActiveStatistics().readLocked();
    mBatteryStatsService.getActiveStatistics().writeAsyncLocked();
   mOnBattery = DEBUG_POWER ? true
               : mBatteryStatsService.getActiveStatistics().getIsOnBattery();
   mBatteryStatsService.getActiveStatistics().setCallback(this);
 
    //创建USS
    mUsageStatsService= new UsageStatsService(new File(
               systemDir, "usagestats").toString());
    //获取OpenGl版本
   GL_ES_VERSION = SystemProperties.getInt("ro.opengles.version",
           ConfigurationInfo.GL_ES_VERSION_UNDEFINED);
     //mConfiguration类型为Configuration，用于描述资源文件的配置属性，例如
     //字体、语言等。后文再讨论这方面的内容
    mConfiguration.setToDefaults();
    mConfiguration.locale = Locale.getDefault();
     //mProcessStats为ProcessStats类型，用于统计CPU、内存等信息。其内部工作原理就是
    //读取并解析/proc/stat文件的内容。该文件由内核生成，用于记录kernel及system
    //一些运行时的统计信息。读者可在Linux系统上通过man proc命令查询详细信息
    mProcessStats.init();
 
     //解析/data/system/packages-compat.xml文件，该文件用于存储那些需要考虑屏幕尺寸
    //的APK的一些信息。读者可参考AndroidManifest.xml中compatible-screens相关说明。
    //当APK所运行的设备不满足要求时，AMS会根据设置的参数以采用屏幕兼容的方式去运行它
    mCompatModePackages = new CompatModePackages(this, systemDir);
 
     Watchdog.getInstance().addMonitor(this);
     //创建一个新线程，用于定时更新系统信息（和mProcessStats交互）
    mProcessStatsThread = new Thread("ProcessStats") {...//先略去该段代码}
    mProcessStatsThread.start();
 }