ActivityManagerService 启动过程

一、概述

本文以AMS为主线，讲述system_server进程中AMS服务的启动过程，以startBootstrapServices()方法为起点，紧跟着startCoreServices(), startOtherServices()共3个方法。

frameworks/base/services/java/com/android/server/
  - SystemServer.java

frameworks/base/services/core/java/com/android/server/
  - SystemServiceManager.java
  - ServiceThread.java
  - am/ActivityManagerService.java

frameworks/base/core/java/android/app/
  - ActivityThread.java
  - LoadedApk.java
  - ContextImpl.java

二. AMS启动过程

2.1 startBootstrapServices

[-> SystemServer.java]

private void startBootstrapServices() {
    ...
    //启动AMS服务【见小节2.2】
    mActivityManagerService = mSystemServiceManager.startService(
            ActivityManagerService.Lifecycle.class).getService();

    //设置AMS的系统服务管理器
    mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
    //设置AMS的APP安装器
    mActivityManagerService.setInstaller(installer);
    //初始化AMS相关的PMS
    mActivityManagerService.initPowerManagement();
    ...

    //设置SystemServer【见小节2.3】
    mActivityManagerService.setSystemProcess();
}

2.2 启动AMS服务

SystemServiceManager.startService(ActivityManagerService.Lifecycle.class) 功能主要：

1. 创建ActivityManagerService.Lifecycle对象；
2. 调用Lifecycle.onStart()方法。

2.1.1 AMS.Lifecycle

[-> ActivityManagerService.java]

public static final class Lifecycle extends SystemService {
    private final ActivityManagerService mService;

    public Lifecycle(Context context) {
        super(context);
        //创建ActivityManagerService【见小节2.1.2】
        mService = new ActivityManagerService(context);
    }

    @Override
    public void onStart() {
        mService.start();  //【见小节2.1.3】
    }

    public ActivityManagerService getService() {
        return mService;
    }
}

该过程：创建AMS内部类的Lifecycle，已经创建AMS对象，并调用AMS.start();

2.1.2 AMS创建

public ActivityManagerService(Context systemContext) {
    mContext = systemContext;
    mFactoryTest = FactoryTest.getMode();//默认为FACTORY_TEST_OFF
    mSystemThread = ActivityThread.currentActivityThread();

    //创建名为"ActivityManager"的前台线程，并获取mHandler
    mHandlerThread = new ServiceThread(TAG, android.os.Process.THREAD_PRIORITY_FOREGROUND, false);
    mHandlerThread.start();

    mHandler = new MainHandler(mHandlerThread.getLooper());

    //通过UiThread类，创建名为"android.ui"的线程
    mUiHandler = new UiHandler();

    //前台广播接收器，在运行超过10s将放弃执行
    mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
            "foreground", BROADCAST_FG_TIMEOUT, false);
    //后台广播接收器，在运行超过60s将放弃执行
    mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
            "background", BROADCAST_BG_TIMEOUT, true);
    mBroadcastQueues[0] = mFgBroadcastQueue;
    mBroadcastQueues[1] = mBgBroadcastQueue;

    //创建ActiveServices，其中非低内存手机mMaxStartingBackground为8
    mServices = new ActiveServices(this);
    mProviderMap = new ProviderMap(this);

    //创建目录/data/system
    File dataDir = Environment.getDataDirectory();
    File systemDir = new File(dataDir, "system");
    systemDir.mkdirs();

    //创建服务BatteryStatsService
    mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);
    mBatteryStatsService.getActiveStatistics().readLocked();
    ...

    //创建进程统计服务，信息保存在目录/data/system/procstats，
    mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));

    mAppOpsService = new AppOpsService(new File(systemDir, "appops.xml"), mHandler);
    mGrantFile = new AtomicFile(new File(systemDir, "urigrants.xml"));

    // User 0是第一个，也是唯一的一个开机过程中运行的用户
    mStartedUsers.put(UserHandle.USER_OWNER, new UserState(UserHandle.OWNER, true));
    mUserLru.add(UserHandle.USER_OWNER);
    updateStartedUserArrayLocked();
    ...

    //CPU使用情况的追踪器执行初始化
    mProcessCpuTracker.init();
    ...
    mRecentTasks = new RecentTasks(this);
    // 创建ActivityStackSupervisor对象
    mStackSupervisor = new ActivityStackSupervisor(this, mRecentTasks);
    mTaskPersister = new TaskPersister(systemDir, mStackSupervisor, mRecentTasks);

    //创建名为"CpuTracker"的线程
    mProcessCpuThread = new Thread("CpuTracker") {
        public void run() {
          while (true) {
              synchronized(this) {
                final long now = SystemClock.uptimeMillis();
                long nextCpuDelay = (mLastCpuTime.get()+MONITOR_CPU_MAX_TIME)-now;
                long nextWriteDel