Android 系统架构 —— AMS 的启动

public class ActivityManagerService extends IActivityManager.Stub
        implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
        
    private void startBootstrapServices() {
        ......
        // 3.1 启动 AMS
        mActivityManagerService = mSystemServiceManager.startService(
                ActivityManagerService.Lifecycle.class).getService();
        mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
        ......
        // 3.3 AMS 设置系统服务进程的程序
        mActivityManagerService.setSystemProcess();
        ......
    }
    
    private void startOtherServices() {
        // 安装系统 Provider
        mActivityManagerService.installSystemProviders();
        ......
        // 3.5 所有服务初始化完毕了, 调用 AMS 的 systemReady
        mActivityManagerService.systemReady(new Runnable() {
            public void run() {
                // 启动服务 "com.android.systemui" 和 "com.android.systemui.SystemUIService"
                startSystemUi(context);
                // 调用其他服务的 systemReady 方法
                ...
                // 调用其他服务的 systemRunning 方法
                ...
            }
         });
         ......
    }
    
}

public class ActivityManagerService extends IActivityManager.Stub {
    
    public static final class Lifecycle extends SystemService {
    
        private final ActivityManagerService mService;
        
        @Override
        public void onStart() {
            mService.start();
        }
        
    }
    
    private void start() {
        // 移除所有的进程组
        removeAllProcessGroups();
        // mProcessCpuThread 在 AMS 的构造函数中创建, 这里启动它
        mProcessCpuThread.start();
        // 发布电池统计服务
        mBatteryStatsService.publish();
        mAppOpsService.publish(mContext);
        ......
        // 创建 LocalService
        LocalServices.addService(ActivityManagerInternal.class, new LocalService());
        ......
        try {
            mProcessCpuInitLatch.await();
        } catch (InterruptedException e) {
            ......
        }
    }
    
}

public class ActivityManagerService extends IActivityManager.Stub { 
    
    public void setSystemProcess() {
        try {
            // 注册自己
            ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
                    DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
            // 注册进程统计服务
            ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
            // 注册内存信息服务
            ServiceManager.addService("meminfo", new MemBinder(this), /* allowIsolated= */ false,
                    DUMP_FLAG_PRIORITY_HIGH);
            // 注册图像信息服务
            ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
            // 注册数据库服务
            ServiceManager.addService("dbinfo", new DbBinder(this));
            if (MONITOR_CPU_USAGE) {
                // 注册 CPU 信息服务
                ServiceManager.addService("cpuinfo", new CpuBinder(this),
                        /* allowIsolated= */ false, DUMP_FLAG_PRIORITY_CRITICAL);
            }
            // 注册权限控制服务
            ServiceManager.addService("permission", new PermissionController(this));
            // 注册进程信息服务
            ServiceManager.addService("processinfo", new ProcessInfoService(this));

            ApplicationInfo info = mContext.getPackageManager().getApplicationInfo(
                    "android", STOCK_PM_FLAGS | MATCH_SYSTEM_ONLY);
            mSystemThread.installSystemApplicationInfo(info, getClass().getClassLoader());
            synchronized (this) {
                // 注册当前进程的记录
                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);
                }
                // 维护进程的 LRU
                updateLruProcessLocked(app, false, null);
                updateOomAdjLocked();
            }
        } catch (PackageManager.NameNotFoundException e) {
            ......
        }
        ......
    }
    
}

public class ActivityManagerService extends IActivityManager.Stub { 

    public void systemReady(final Runnable goingCallback, TimingsTraceLog traceLog) {
        ......
        // 1. 准备 AMS 
        // 将非 persistent 进程加入 procsToKill 中, 到后面进行杀进程操作
        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);
                }
            }
        }
        // 执行杀进程操作
        synchronized(this) {
            if (procsToKill != null) {
                for (int i=procsToKill.size()-1; i>=0; i--) {
                    ProcessRecord proc = procsToKill.get(i);
                     ......
                    removeProcessLocked(proc, true, false, "system update done");
                }
            }
            ......
            mProcessesReady = true;
        }
        ......
        // 2. 执行 goingCallback 回调, 准备其他服务
        if (goingCallback != null) goingCallback.run();
        ......
        // 3. 启动 App
        synchronized (this) {
            // 启动持久化的 App
            startPersistentApps(PackageManager.MATCH_DIRECT_BOOT_AWARE);
            // Start up initial activity.
            mBooting = true;
            // 启动 Launcher
            startHomeActivityLocked(currentUserId, "systemReady");
            ......
            // 恢复栈顶 Activity 的启动
            mStackSupervisor.resumeFocusedStackTopActivityLocked();
        }
    }
    
}