android 系统启动 AMS

ActivityManagerService启动过程

Posted by Gityuan on February 21, 2016

基于Android 6.0的源码剖析， 分析Android系统服务ActivityManagerService，简称AMS

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

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

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

一、概述

Android系统启动-SystemServer篇(二)中有讲到AMS，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。

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 nextWriteDelay = (mLastWriteTime+BATTERY_STATS_TIME)-now;
                if (nextWriteDelay < nextCpuDelay) {
                    nextCpuDelay = nextWriteDelay;
                }
                if (nextCpuDelay > 0) {
                    mProcessCpuMutexFree.set(true);
                    this.wait(nextCpuDelay);
                }
              }
              updateCpuStatsNow(); //更新CPU状态
          }
        }
    };
    ...
}

该过程共创建了3个线程，分别为”ActivityManager”，”android.ui”，”CpuTracker”。

2.1.3 AMS.start

private void start() {
    Process.removeAllProcessGroups(); //移除所有的进程组
    mProcessCpuThread.start(); //启动CpuTracker线程

    mBatteryStatsService.publish(mContext); //启动电池统计服务
    mAppOpsService.publish(mContext);
    //创建LocalService，并添加到LocalServices
    LocalServices.addService(ActivityManagerInternal.class, new LocalService());
}

2.3 AMS.setSystemProcess

public void setSystemProcess() {
    try {
        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));
        ApplicationInfo info = mContext.getPackageManager().getApplicationInfo(
                "android", STOCK_PM_FLAGS);

        //【见小节2.3.1】
        mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
        synchronized (this) {
            //创建ProcessRecord对象
            ProcessRecord app = newProcessRecordLocked(info, info.processName, false, 0);
            app.persistent = true; //设置为persistent进程
            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);//维护进程lru
            updateOomAdjLocked(); //更新adj
        }
    } catch (PackageManager.NameNotFoundException e) {
        throw new RuntimeException("", e);
    }
}

该方法主要工作是注册各种服务。

2.3.1 AT.installSystemApplicationInfo

[-> ActivityThread.java]

public void installSystemApplicationInfo(ApplicationInfo info, ClassLoader classLoader) {
    synchronized (this) {
        getSystemContext().installSystemApplicationInfo(info, classLoader);
        mProfiler = new Profiler();    //创建用于性能统计的Profiler对象
    }
}

该方法调用ContextImpl的nstallSystemApplicationInfo()方法，最终调用LoadedApk的installSystemApplicationInfo，加载名为“android”的package

2.3.2 installSystemApplicationInfo

[-> LoadedApk.java]

void installSystemApplicationInfo(ApplicationInfo info, ClassLoader classLoader) {
    assert info.packageName.equals("android");
    mApplicationInfo = info; //将包名为"android"的应用信息保存到mApplicationInfo
    mClassLoader = classLoader;
}

2.4 startOtherServices

private void startOtherServices() {
  ...
  //安装系统Provider 【见小节2.4.1】
  mActivityManagerService.installSystemProviders();
  ...

  //phase480 && 500
  mSystemServiceManager.startBootPhase(SystemService.PHASE_LOCK_SETTINGS_READY);
  mSystemServiceManager.startBootPhase(SystemService.PHASE_SYSTEM_SERVICES_READY);
  ...

  //【见小节3.1】
  mActivityManagerService.systemReady(new Runnable() {
     public void run() {
         //phase550
         mSystemServiceManager.startBootPhase(
                 SystemService.PHASE_ACTIVITY_MANAGER_READY);
         ...
         //phase600
         mSystemServiceManager.startBootPhase(
                 SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);
         ...
      }
  }
}

2.4.1 AMS.installSystemProviders

public final void installSystemProviders() {
    List<ProviderInfo> providers;
    synchronized (this) {
        ProcessRecord app = mProcessNames.get("system", Process.SYSTEM_UID);
        providers = generateApplicationProvidersLocked(app);
        if (providers != null) {
            for (int i=providers.size()-1; i>=0; i--) {
                ProviderInfo pi = (ProviderInfo)providers.get(i);
                //移除非系统的provider
                if ((pi.applicationInfo.flags&ApplicationInfo.FLAG_SYSTEM) == 0) {
                    providers.remove(i);
                }
            }
        }
    }
    if (providers != null) {
        //安装所有的系统provider
        mSystemThread.installSystemProviders(providers);
    }

    // 创建核心Settings Observer，用于监控Settings的改变。
    mCoreSettingsObserver = new CoreSettingsObserver(this);
}

三. AMS.systemReady

AMS.systemReady()方法的参数为Runable类型的goingCallback， 该方法执行简单划分以下几部分：

public void systemReady(final Runnable goingCallback) {
    before goingCallback; // 见小节[3.1]
    goingCallback.run(); // 见小节[3.2]
    after goingCallback; // 见小节[3.3]
}

3.1 before goingCallback

synchronized(this) {
    if (mSystemReady) { //首次为flase，则不进入该分支
        if (goingCallback != null) {
                goingCallback.run();
            }
        return;
    }

    mRecentTasks.clear();
    //恢复最近任务栏的task
    mRecentTasks.addAll(mTaskPersister.restoreTasksLocked());
    mRecentTasks.cleanupLocked(UserHandle.USER_ALL);
    mTaskPersister.startPersisting();

    if (!mDidUpdate) {
        if (mWaitingUpdate) {
            return;
        }
        final ArrayList<ComponentName> doneReceivers = new ArrayList<ComponentName>();
        //处于升级过程【见小节3.1.1】
        mWaitingUpdate = deliverPreBootCompleted(new Runnable() {
            public void run() {
                synchronized (ActivityManagerService.this) {
                    mDidUpdate = true;
                }
                showBootMessage(mContext.getText(
                        R.string.android_upgrading_complete),
                        false);
                writeLastDonePreBootReceivers(doneReceivers);
                systemReady(goingCallback);
            }
        }, doneReceivers, UserHandle.USER_OWNER);

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

    mAppOpsService.systemReady();
    mSystemReady = true;
}

ArrayList<ProcessRecord> procsToKill = null;
synchronized(mPidsSelfLocked) {
    for (int i=mPidsSelfLocked.size()-1; i>=0; i--) {
        ProcessRecord proc = mPidsSelfLocked.valueAt(i);
        //非persistent进程,加入procsToKill
        if (!isAllowedWhileBooting(proc.info)){
            if (procsToKill == null) {
                procsToKill = new ArrayList<ProcessRecord>();
            }
            procsToKill.add(proc);
        }
    }
}

synchronized(this) {
    if (procsToKill != null) {
        //杀掉procsToKill中的进程, 杀掉进程且不允许重启
        for (int i=procsToKill.size()-1; i>=0; i--) {
            ProcessRecord proc = procsToKill.get(i);
            removeProcessLocked(proc, true, false, "system update done");
        }
    }
    mProcessesReady = true; //process处于ready状态
}
Slog.i(TAG, "System now ready");
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_AMS_READY,
     SystemClock.uptimeMillis());

该阶段的主要功能：

  • 向PRE_BOOT_COMPLETED的接收者发送广播；
  • 杀掉procsToKill中的进程, 杀掉进程且不允许重启；
  • 此时，系统和进程都处于ready状态；

3.1.1 deliverPreBootCompleted

private boolean deliverPreBootCompleted(final Runnable onFinishCallback,
        ArrayList<ComponentName> doneReceivers, int userId) {
    Intent intent = new Intent(Intent.ACTION_PRE_BOOT_COMPLETED);
    List<ResolveInfo> ris = AppGlobals.getPackageManager().queryIntentReceivers(
                intent, null, 0, userId);

    //对于FLAG_SYSTEM=false的app直接过滤掉
    for (int i=ris.size()-1; i>=0; i--) {
        if ((ris.get(i).activityInfo.applicationInfo.flags
                &ApplicationInfo.FLAG_SYSTEM) == 0) {
            ris.remove(i);
        }
    }
    intent.addFlags(Intent.FLAG_RECEIVER_BOOT_UPGRADE);

    if (userId == UserHandle.USER_OWNER) {
        ArrayList<ComponentName> lastDoneReceivers = readLastDonePreBootReceivers();
        for (int i=0; i<ris.size(); i++) {
            ActivityInfo ai = ris.get(i).activityInfo;
            ComponentName comp = new ComponentName(ai.packageName, ai.name);
            if (lastDoneReceivers.contains(comp)) {
                ris.remove(i);
                i--;
                doneReceivers.add(comp);
            }
        }
    }
    ...

    PreBootContinuation cont = new PreBootContinuation(intent, onFinishCallback,
            doneReceivers, ris, users);  //【见小节3.1.2】
    cont.go(); //【见小节3.1.3】
    return true;
}

3.1.2 PreBootContinuation

[-> ActivityManagerService.java ::PreBootContinuation]

final class PreBootContinuation extends IIntentReceiver.Stub {

    PreBootContinuation(Intent _intent, Runnable _onFinishCallback,
            ArrayList<ComponentName> _doneReceivers, List<ResolveInfo> _ris, int[] _users) {
        intent = _intent;
        onFinishCallback = _onFinishCallback;
        doneReceivers = _doneReceivers;
        ris = _ris;
        users = _users;
    }
}

3.1.3 PreBootContinuation.go

void go() {
    if (lastRi != curRi) {
        ActivityInfo ai = ris.get(curRi).activityInfo;
        ComponentName comp = new ComponentName(ai.packageName, ai.name);
        intent.setComponent(comp);
        doneReceivers.add(comp);
        lastRi = curRi;
        CharSequence label = ai.loadLabel(mContext.getPackageManager());
        showBootMessage(mContext.getString(R.string.android_preparing_apk, label), false);
    }

    //发送广播
    broadcastIntentLocked(null, null, intent, null, this,
            0, null, null, null, AppOpsManager.OP_NONE,
            null, true, false, MY_PID, Process.SYSTEM_UID, users[curUser]);
}

3.2 goingCallback.run()

此处的goingCallback,便是在startOtherServices()过程中传递进来的参数

private void startOtherServices() {
  ...
  mActivityManagerService.systemReady(new Runnable() {
    public void run() {
      //phase550
      mSystemServiceManager.startBootPhase(
              SystemService.PHASE_ACTIVITY_MANAGER_READY);

      mActivityManagerService.startObservingNativeCrashes();
      //启动WebView
      WebViewFactory.prepareWebViewInSystemServer();
      //启动系统UI【见小节3.2.1】
      startSystemUi(context);

      // 执行一系列服务的systemReady方法
      networkScoreF.systemReady();
      networkManagementF.systemReady();
      networkStatsF.systemReady();
      networkPolicyF.systemReady();
      connectivityF.systemReady();
      audioServiceF.systemReady();
      Watchdog.getInstance().start(); //Watchdog开始工作

      //phase600
      mSystemServiceManager.startBootPhase(
              SystemService.PHASE_THIRD_PARTY_APPS_CAN_START);

      //执行一系列服务的systemRunning方法
      wallpaper.systemRunning();
      inputMethodManager.systemRunning(statusBarF);
      location.systemRunning();
      countryDetector.systemRunning();
      networkTimeUpdater.systemRunning();
      commonTimeMgmtService.systemRunning();
      textServiceManagerService.systemRunning();
      assetAtlasService.systemRunning();
      inputManager.systemRunning();
      telephonyRegistry.systemRunning();
      mediaRouter.systemRunning();
      mmsService.systemRunning();
    }
  });
}

该过程启动各种进程：

  • 启动阶段550，回调相应onBootPhase()方法；
  • 启动WebView，并且会创建进程，这是zygote正式创建的第一个进程；
  • 启动systemui服务；
  • …

3.2.1 startSystemUi

static final void startSystemUi(Context context) {
    Intent intent = new Intent();
    intent.setComponent(new ComponentName("com.android.systemui",
                "com.android.systemui.SystemUIService"));
    context.startServiceAsUser(intent, UserHandle.OWNER);
}

启动服务”com.android.systemui/.SystemUIService”

3.3 after goingCallback

//启动【见小节3.3.1】
mSystemServiceManager.startUser(mCurrentUserId);
synchronized (this) {
    if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
        //通过pms获取所有的persistent进程
        List apps = AppGlobals.getPackageManager().
            getPersistentApplications(STOCK_PM_FLAGS);
        if (apps != null) {
            int N = apps.size();
            int i;
            for (i=0; i<N; i++) {
                ApplicationInfo info = (ApplicationInfo)apps.get(i);
                if (info != null && !info.packageName.equals("android")) {
                    //启动persistent进程
                    addAppLocked(info, false, null);
                }
            }
        }
    }

    mBooting = true;
    // 启动桌面Activity 【见小节3.3.2】
    startHomeActivityLocked(mCurrentUserId, "systemReady");

    ...
    long ident = Binder.clearCallingIdentity();
    try {
        //system发送广播USER_STARTED
        Intent intent = new Intent(Intent.ACTION_USER_STARTED);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
                | Intent.FLAG_RECEIVER_FOREGROUND);
        intent.putExtra(Intent.EXTRA_USER_HANDLE, mCurrentUserId);
        broadcastIntentLocked(...);  

        //system发送广播USER_STARTING
        intent = new Intent(Intent.ACTION_USER_STARTING);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
        intent.putExtra(Intent.EXTRA_USER_HANDLE, mCurrentUserId);
        broadcastIntentLocked(...);
    } finally {
        Binder.restoreCallingIdentity(ident);
    }

    mStackSupervisor.resumeTopActivitiesLocked();
    sendUserSwitchBroadcastsLocked(-1, mCurrentUserId);
}

该阶段主要功能：

  • 回调所有SystemService的onStartUser()方法；
  • 启动persistent进程；
  • 启动home Activity;
  • 发送广播USER_STARTED和USER_STARTING；
  • 恢复栈顶Activity;
  • 发送广播USER_SWITCHED；

3.3.1 SSM.startUser

[-> SystemServiceManager.java]

public void startUser(final int userHandle) {
    final int serviceLen = mServices.size();
    for (int i = 0; i < serviceLen; i++) {
        final SystemService service = mServices.get(i);
        try {
            //回调所有SystemService的onStartUser()方法
            service.onStartUser(userHandle);
        } catch (Exception ex) {
            ...
        }
    }
}

3.3.2 AMS.startHomeActivityLocked

boolean startHomeActivityLocked(int userId, String reason) {
    //home intent有CATEGORY_HOME
    Intent intent = getHomeIntent();
    ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);
    if (aInfo != null) {
        intent.setComponent(new ComponentName(
                aInfo.applicationInfo.packageName, aInfo.name));
        aInfo = new ActivityInfo(aInfo);
        aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);
        ProcessRecord app = getProcessRecordLocked(aInfo.processName,
                aInfo.applicationInfo.uid, true);
        if (app == null || app.instrumentationClass == null) {
            intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
            //启动桌面Activity
            mStackSupervisor.startHomeActivity(intent, aInfo, reason);
        }
    }
    return true;
}

四. 总结

  1. 创建AMS实例对象，创建Andoid Runtime，ActivityThread和Context对象；
  2. setSystemProcess：注册AMS、meminfo、cpuinfo等服务到ServiceManager；
  3. installSystemProviderss，加载SettingsProvider；
  4. 启动SystemUIService，再调用一系列服务的systemReady()方法；

4.1 发布Binder服务

[小节2.3]的AMS.setSystemProcess()过程向servicemanager注册了如下这个binder服务

服务名 类名 功能
activity ActivityManagerService AMS
procstats ProcessStatsService 进程统计
meminfo MemBinder 内存
gfxinfo GraphicsBinder 图像信息
dbinfo DbBinder 数据库
cpuinfo CpuBinder CPU
permission PermissionController 权限
processinfo ProcessInfoService 进程服务
usagestats UsageStatsService 应用的使用情况

想要查看这些服务的信息，可通过dumpsys <服务名>命令。比如查看CPU信息命令dumpsys cpuinfo。

4.2 AMS.systemReady

另外，AMS.systemReady()的大致过程如下:

public final class ActivityManagerService{

    public void systemReady(final Runnable goingCallback) {
        ...//更新操作
        mSystemReady = true; //系统处于ready状态
        removeProcessLocked(proc, true, false, "system update done");//杀掉所有非persistent进程
        mProcessesReady = true;  //进程处于ready状态

        goingCallback.run(); //这里有可能启动进程

        addAppLocked(info, false, null); //启动所有的persistent进程
        mBooting = true;  //正在启动中
        startHomeActivityLocked(mCurrentUserId, "systemReady"); //启动桌面
        mStackSupervisor.resumeTopActivitiesLocked(); //恢复栈顶的Activity
    }
}

再说一说mProcessesReady：

startProcessLocked()过程对于非persistent进程必须等待mProcessesReady = true才会真正创建进程，否则进程放入mProcessesOnHold队列。 当然以下情况不会判断mProcessesReady：

  • addAppLocked()启动persistent进程; //但此时已经mProcessesReady；
  • finishBooting()启动on-hold进程; //但此时已经mProcessesReady；
  • cleanUpApplicationRecordLock() //启动需要restart进程，前提是进程已创建；
  • attachApplicationLocked() //绑定Bind死亡通告失败，前台同样是进程要已创建。

还有一个特殊情况，可以创建进程：processNextBroadcast()过程对于flag为FLAG_RECEIVER_BOOT_UPGRADE的广播拉进程 ，只在小节3.1.1的升级过程会出现。

由此可见，mProcessesReady在没有ready前，则基本没有应用进程。

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