ActivityManagerService启动过程分析

之前讲Android的View的绘制原理和流程的时候，讲到过在Android调用setContentView之后，Android调用了一个prepreTravle的方法,这里面就提到了ActivityManagerService。

ActivityManagerService提供的主要功能：
       （1）统一调度各应用程序的Activity
       （2）内存管理
       （3）进程管理

上一篇我们分析Android启动过程的文章中我们分析到了SystemServer，当时我们只是简单的描述了下，Android启动过程分析，我们还是来看一张启动的流程图，

System Server代码位于：//frameworks\base\services\java\com\android\server\SystemServer.java

我们来看一段启动的代码：

private void run() {

    // 准备SystemServer运行环境:设置线程优先级，创建主线层Looper，ActivityThread和SystemContext
    android.os.Process.setThreadPriority();
    Looper.prepareMainLooper();

    // 创建systemserver上进程的ActivityThread和SystemContext
    createSystemContext();

    // 增加SystemServiceManager：统一管理system services的创建，启动和生命周期，多用户切换
    mSystemServiceManager = new SystemServiceManager(mSystemContext);

    // Start services.

    // 1.创建AMS
    mActivityManagerService = mSystemServiceManager.startService(
            ActivityManagerService.Lifecycle.class).getService();

    // Start the Power Manager service
    mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);

    // Start the package manager service
    mPackageManagerService = PackageManagerService.main();

    // 2.将SystemServer进程可加到AMS中调度管理
    mActivityManagerService.setSystemProcess();

    // 3.将相关provider运行在systemserver进程中：SettingsProvider
    mActivityManagerService.installSystemProviders();

    //
    final Watchdog watchdog = Watchdog.getInstance();
    watchdog.init(context, mActivityManagerService);

    // Start Window Manager
    wm = WindowManagerService.main();

    // 4.直接保存wms对象，与WMS交互
    mActivityManagerService.setWindowManager(wm);

    // 5.通过WMS 弹出“正在启动应用”框
    // R.string.android_upgrading_starting_apps
    ActivityManagerNative.getDefault().showBootMessage();

    // 6. AMS作为Framework核心，做好准备就绪后就开始启动应用层，和对AMS有依赖的服务
    mActivityManagerService.systemReady(new Runnable(){
        //启动SystemUI
        startSystemUi(context);

        //启动WatchDog监控核心服务状态
        Watchdog.getInstance().start();

        //
        mmsServiceF.systemRunning();
    });

    // Loop forever.
    Looper.loop();
}

上面的6个步骤就是SystemServer中关于AMS的调用，完成AMS的创建和系统的初始化，以及与WMS交互等流程。

一、ActivityManagerService 创建过程

mActivityManagerService = mSystemServiceManager.startService(
　　　　　　　　　　　　ActivityManagerService.Lifecycle.class).getService();

通过SystemServiceManager这样一个模板类来创建运行在SystemServer中的Framework服务。并将创建的服务统一保存在队列管理。

public ActivityManagerService(Context systemContext) {

　　     // 1.系统Context 和 ActivityThread （将systemserver进程作为应用进程管理）
        mContext = systemContext;
        mFactoryTest = FactoryTest.getMode();
        mSystemThread = ActivityThread.currentActivityThread();

        // 2.AMS工作的线程和Handler，处理显示相关的UiHandler  ---》知识点HandlerThread和Handler
        mHandlerThread = new ServiceThread(TAG,
            android.os.Process.THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
        mHandlerThread.start();
        mHandler = new MainHandler(mHandlerThread.getLooper());
        mUiHandler = new UiHandler();

        // 3. 广播队列BroadcastQueue初始化：前台广播队列和后台广播队列
        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;

        // 4. Service 和 Provider 管理
        mServices = new ActiveServices(this);
        mProviderMap = new ProviderMap(this);

        // 5.系统数据存放目录：/data/system/
        File dataDir = Environment.getDataDirectory();
        File systemDir = new File(dataDir, "system");
        systemDir.mkdirs();

        // 电池状态信息，进程状态 和 应用权限管理
        mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);
        mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));
        mAppOpsService = new AppOpsService(new File(systemDir, "appops.xml"), mHandler);

        // 6.多用户管理
        mStartedUsers.put(UserHandle.USER_OWNER, new UserState(UserHandle.OWNER, true));
        mUserLru.add(UserHandle.USER_OWNER);
        updateStartedUserArrayLocked();

        // 7.最近任务，Activity，Task管理
        mRecentTasks = new RecentTasks(this);
        mStackSupervisor = new ActivityStackSupervisor(this, mRecentTasks);
        mTaskPersister = new TaskPersister(systemDir, mStackSupervisor, mRecentTasks);

        // 创建一个新线程，用于监控和定时更新系统CPU信息，30分钟更新一次CPU和电池信息
        mProcessCpuTracker.init();
        mProcessCpuThread = new Thread("CpuTracker") {}

        // 加入Watchdog监控起来
        Watchdog.getInstance().addMonitor(this);
        Watchdog.getInstance().addThread(mHandler);
    }

二、将SystemServer进程可加到AMS中调度管理

mActivityManagerService.setSystemProcess();

mActivityManagerService将system扔到ams统一管理和调度

public void setSystemProcess() {
        // 将服务加入到ServiceManager中
        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));

        // 设置application info LoadedApkinfo 有关 framework-res.apk
        ApplicationInfo info = mContext.getPackageManager().getApplicationInfo(
                    "android", STOCK_PM_FLAGS);
        mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());

        //给SystemServer进程创建ProcessRecord，adj值，就是将SystemServer进程加入到AMS进程管理机制中，跟应用进程一致
        synchronized (this) {
            ProcessRecord app = newProcessRecordLocked(info, info.processName, false, 0);
            app.persistent = true;
            app.pid = MY_PID;
            app.maxAdj = ProcessList.SYSTEM_ADJ;
            app.makeActive(mSystemThread.getApplicationThread(), mProcessStats);
            synchronized (mPidsSelfLocked) {
                mPidsSelfLocked.put(app.pid, app);
            }
            updateLruProcessLocked(app, false, null);
            updateOomAdjLocked();
        }
    }

这一步就是给SystemServer进程创建ProcessRecord，adj值，就是将SystemServer进程加入到AMS进程管理。

三、创建运行在SystemServer进程中Provider

mActivityManagerService.installSystemProviders();

取出进程名为"system"，user_id为SYSTEM_UID的进程信息 ，生成运行在system进程中的providerInfo，并交给上下文的Provider。这段代码的任务就是查询与安装Content Provider并且发布，其中查询出来的provider为SettingsProvider

public final void installSystemProviders() {
        List<ProviderInfo> providers;
        synchronized (this) {
            //取出进程名为"system"，user_id为SYSTEM_UID的进程信息
            ProcessRecord app = mProcessNames.get("system", Process.SYSTEM_UID);
            //生成运行在system进程中的providerInfo，表示一个Content Provider。
            providers = generateApplicationProvidersLocked(app);
            if (providers != null) {
                for (int i=providers.size()-1; i>=0; i--) {
                    ProviderInfo pi = (ProviderInfo)providers.get(i);
                    //过滤掉非系统apk
                    if ((pi.applicationInfo.flags&ApplicationInfo.FLAG_SYSTEM) == 0) {
                        Slog.w(TAG, "Not installing system proc provider " + pi.name
                                + ": not system .apk");
                        providers.remove(i);
                    }
                }
            }
        }
        if (providers != null) {
           //安装provider
            mSystemThread.installSystemProviders(providers);
        }
        //监听Settings数据库变化。
        mCoreSettingsObserver = new CoreSettingsObserver(this);  

        //mUsageStatsService.monitorPackages();

四、AMS systemReady过程

mActivityManagerService.systemReady();

发送ACTION_PRE_BOOT_COMPLETE方法，清理启动的persistent进程，读取Settings配置，运行runnable接口，启动SystemUI，启动persistent应用程序，启动home，发送ACTION_BOOT_COMPLETE广播

public void systemReady(final Runnable goingCallback) {
        synchronized(this) {
            if (mSystemReady) {
                goingCallback.run();
            }
            ……

            // 1.升级相关处理：发送PRE_BOOT_COMPLETED广播 等待升级处理完成才能继续
            // Check to see if there are any update receivers to run.
            if (!mDidUpdate) {
                // 等待升级完成，否则直接返回
                if (mWaitingUpdate) {
                    return;
                }
                // 发送PRE_BOOT_COMPLETED广播
                final ArrayList<ComponentName> doneReceivers = new ArrayList<ComponentName>();
                mWaitingUpdate = deliverPreBootCompleted(new Runnable() {
                    // 等待所有接收PRE_BOOT_COMPLETED广播者处理完毕
                    public void run() {
                        synchronized (ActivityManagerService.this) {
                            mDidUpdate = true;
                        }
                        showBootMessage(mContext.getText(
                                R.string.android_upgrading_complete),
                                false);

                        // 将系统版本号和处理过的广播写入文件：/data/system/called_pre_boots.dat文件
                        writeLastDonePreBootReceivers(doneReceivers);

                        // 继续systemReady流程
                        systemReady(goingCallback);
                    }
                }, doneReceivers, UserHandle.USER_OWNER);

                if (mWaitingUpdate) {
                    return;
                }
                mDidUpdate = true;
            }

            mSystemReady = true;
        }

        // 2. 收集已经启动的进程并杀死，除过persistent常驻进程
        ArrayList<ProcessRecord> procsToKill = null;
        synchronized(mPidsSelfLocked) {
            for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {
                ProcessRecord proc = mPidsSelfLocked.valueAt(i);
                if (!isAllowedWhileBooting(proc.info)){
                    if (procsToKill == null) {
                        procsToKill = new ArrayList<ProcessRecord>();
                    }
                    procsToKill.add(proc);
                }
            }
        }

        synchronized(this) {
            if (procsToKill != null) {
                for (int i=procsToKill.size()-1; i>=0; i--) {
                    ProcessRecord proc = procsToKill.get(i);
                    Slog.i(TAG, "Removing system update proc: " + proc);
                    removeProcessLocked(proc, true, false, "system update done");
                }
            }

            // Now that we have cleaned up any update processes, we
            // are ready to start launching real processes and know that
            // we won't trample on them any more.
            mProcessesReady = true;
        }

        // 3.系统准备好后回调传入的Runnable：
        if (goingCallback != null) goingCallback.run();

　　　　
　　　　　　// 4. 发送账户启动的广播，涉及多用户
　　　　　　long ident = Binder.clearCallingIdentity();

　　　　　　Intent intent = new Intent(Intent.ACTION_USER_STARTED);
　　　　　　broadcastIntentLocked(intent);
　　　　　　intent = new Intent(Intent.ACTION_USER_STARTING);
　　　　　　broadcastIntentLocked(intent);

　　　　　　Binder.restoreCallingIdentity(ident);

        // 5. 启动桌面Home Activity
        mBooting = true;
        startHomeActivityLocked(mCurrentUserId, "systemReady");
        mStackSupervisor.resumeTopActivitiesLocked();
  }

参考：

http://www.cnblogs.com/bastard/p/5770573.html

http://blog.csdn.net/u010083774/article/details/50620355