ActivityManagerService启动过程分析

/**
 * The main entry point from zygote.
 */
public static void main(String[] args) {
    new SystemServer().run();
}

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();
}

　　// Note: This method is invoked on the main thread but may need to attach various
    // handlers to other threads.  So take care to be explicit about the looper.
    public ActivityManagerService(Context systemContext) {
        
　　     // 1.系统Context 和 ActivityThread
        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);
    }

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();
        }
    }

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

deliverPreBootCompleted(new Runnable() {
        // 向PMS查询，所有接收ACTION_PRE_BOOT_COMPLETED广播的Receiver
        Intent intent = new Intent(Intent.ACTION_PRE_BOOT_COMPLETED);
        List<ResolveInfo> ris = null;
        ris = AppGlobals.getPackageManager().queryIntentReceivers(
                    intent, null, 0, userId);
        
        // 只有系统广播才能接收该广播，去掉非系统应用
        for (int i=ris.size()-1; i>=0; i--) {
            if ((ris.get(i).activityInfo.applicationInfo.flags
                &ApplicationInfo.FLAG_SYSTEM) == 0) {
            ris.remove(i);
            }
        }
        
        // 给Intent设置flag：FLAG_RECEIVER_BOOT_UPGRADE，很关键这个看看flag的作用：
        // 只有设置这个标志，才能让应用在系统没有ready的情况下启动，见下文原始注释
        intent.addFlags(Intent.FLAG_RECEIVER_BOOT_UPGRADE);
        
        // 将已经处理过ACTION_PRE_BOOT_COMPLETED广播的Receiver去掉
        // 已经处理该广播的Receiver记录 和 对应的系统版本号 都记录在：/data/system/called_pre_boots.dat文件中，
        // 通过与系统当前版本号比对，确认是否已处理过。考虑处理过程异常中断的情况：比如断电
        ArrayList<ComponentName> lastDoneReceivers = readLastDonePreBootReceivers();
        
        // 将已经处理过的广播去除，同时记录已处理过保存在 doneReceivers数组中
        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)) {
                // We already did the pre boot receiver for this app with the current
                // platform version, so don‘t do it again...
                ris.remove(i);
                i--;
                // ...however, do keep it as one that has been done, so we don‘t
                // forget about it when rewriting the file of last done receivers.
                doneReceivers.add(comp);
            }
        }
        
        // 内部类专门用来ACTION_PRE_BOOT_COMPLETED广播的发送，要看看这个PreBootContinuation类
        // 这块逻辑一直在变，Android5.0, 6.0 , 以及看到在7.0上又变了，基本思路不变，本文代码基于Android6.0
        PreBootContinuation cont = new PreBootContinuation(intent, onFinishCallback, doneReceivers,
                ris, users);
        cont.go();
        return true;
    }

给intent设置的广播意义：

    /**

    * Set when this broadcast is for a boot upgrade, a special mode that

    * allows the broadcast to be sent before the system is ready and launches

    * the app process with no providers running in it.

    * @hide

    */

    public static final int FLAG_RECEIVER_BOOT_UPGRADE = 0x02000000;

final class PreBootContinuation extends IIntentReceiver.Stub {
        void go() {
            //判断是不是最后一个接收者
            if (lastRi != curRi) {
                
                // 疑问：如果不是最后一个接收者，则发给一个指定接收者ComponentName
                // 为什么要在这里指定接收者，一个个发送，而不是交给广播自己去处理？
                ActivityInfo ai = ris.get(curRi).activityInfo;
                ComponentName comp = new ComponentName(ai.packageName, ai.name);
                intent.setComponent(comp);
                doneReceivers.add(comp);
                lastRi = curRi;
                
                // 界面显示正在处理的广播，上面的指定接收者，就是为了这里能显示正在处理的广播名称？
                CharSequence label = ai.loadLabel(mContext.getPackageManager());
                showBootMessage(mContext.getString(R.string.android_preparing_apk, label), false);
            }
            
            // 发送广播，指定接收者处理完毕，会resultTo回来--》this
            Slog.i(TAG, "Pre-boot of " + intent.getComponent().toShortString()
                    + " for user " + users[curUser]);
            broadcastIntentLocked(null, null, intent, null, this,
                    0, null, null, null, AppOpsManager.OP_NONE,
                    null, true, false, MY_PID, Process.SYSTEM_UID, users[curUser]);
        }
        
        
        public void performReceive(Intent intent, int resultCode,
                String data, Bundle extras, boolean ordered,
                boolean sticky, int sendingUser) {
                
            // 指定接收者广播处理完毕回调resultTo回来，继续处理下一个，如果所有处理完，则post消息执行onFinishCallback
            curUser++;
            if (curUser >= users.length) {
                curUser = 0;
                curRi++;
                if (curRi >= ris.size()) {
                    // All done sending broadcasts!
                    if (onFinishCallback != null) {
                        // The raw IIntentReceiver interface is called
                        // with the AM lock held, so redispatch to
                        // execute our code without the lock.
                        mHandler.post(onFinishCallback);
                    }
                    return;
                }
            }
            go();
        }
    }

接上面systemReady最后部分：
    // Start up initial activity.
    mBooting = true;
    startHomeActivityLocked(mCurrentUserId, "systemReady");
    mStackSupervisor.resumeTopActivitiesLocked();