深入理解AMS ---  一 AMS 的启动

代码分支：android-9.0.0_r9
combo: aosp_x86_64-eng

一 Zygote fork

Zygote fork SystemServer 的过程如下：

1. ZygoteInit#forkSystemServer

2. ZygoteInit#handleSystemServerProcess

3. ZygoteInit#zygoteInit

4. RuntimeInit#applicationInit

5. RuntimeInit#findStaticMain

1.1 Zygote  fork SystemServer 进程

ZygoteInit#forkSystemServer  配置system_server 的参数，uid gid 进程显示的名字等，然后调用native 的fork, 在子进程中调用handleSystemServerProcess

ZygoteInit.java

private static Runnable forkSystemServer(String abiList, String socketName,
            ZygoteServer zygoteServer) {       
        /* Hardcoded command line to start the system server */
        String args[] = {            "--setuid=1000",            "--setgid=1000",            "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1024,1032,1065,3001,3002,3003,3006,3007,3009,3010",            "--capabilities=" + capabilities + "," + capabilities,            "--nice-name=system_server",            "--runtime-args",            "--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT,            "com.android.server.SystemServer",
        };        try {            /* Request to fork the system server process */
            pid = Zygote.forkSystemServer(
                    parsedArgs.uid, parsedArgs.gid,
                    parsedArgs.gids,
                    parsedArgs.runtimeFlags,                    null,
                    parsedArgs.permittedCapabilities,
                    parsedArgs.effectiveCapabilities);
        } catch (IllegalArgumentException ex) {            throw new RuntimeException(ex);
        }        /* For child process */
        if (pid == 0) {            if (hasSecondZygote(abiList)) {
                waitForSecondaryZygote(socketName);
            }

            zygoteServer.closeServerSocket();            return handleSystemServerProcess(parsedArgs);
        }        return null;
    }

1.2 System_service 进程启动，准备加载的ClassLoader

ZygoteInit.java    private static Runnable handleSystemServerProcess(ZygoteConnection.Arguments parsedArgs) {        // set umask to 0077 so new files and directories will default to owner-only permissions.
       
        if (parsedArgs.invokeWith != null) {

        } else {
            ClassLoader cl = null;            if (systemServerClasspath != null) {
                cl = createPathClassLoader(systemServerClasspath, parsedArgs.targetSdkVersion);

                Thread.currentThread().setContextClassLoader(cl);
            }            /*
             * Pass the remaining arguments to SystemServer.
             */
            return ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
        }        /* should never reach here */
    }

1.3 RuntimeInit 初始化，进一步的准备初始化的环境

ZygoteInit.java    public static final Runnable zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader) {

        RuntimeInit.commonInit();
        ZygoteInit.nativeZygoteInit();        return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
    }

1.4 通过findStaticMain 方法反射调用System_Server 的main 方法。

RuntimeInit.java    protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
            ClassLoader classLoader) {      
        // Remaining arguments are passed to the start class's static main
        return findStaticMain(args.startClass, args.startArgs, classLoader);
    }

二 SystemServer进程

2.1  SystemServer 启动，然后运行 run 方法。

SystemServer.java public static void main(String[] args) {        new SystemServer().run();
    }    public SystemServer() {        // Check for factory test mode.
        mFactoryTestMode = FactoryTest.getMode();        // Remember if it's runtime restart(when sys.boot_completed is already set) or reboot
        mRuntimeRestart = "1".equals(SystemProperties.get("sys.boot_completed"));

        mRuntimeStartElapsedTime = SystemClock.elapsedRealtime();
        mRuntimeStartUptime = SystemClock.uptimeMillis();
    }

2.2 System_Server 的run 方法

1. 开始首先配置 VM 参数

2. Binder 参数，

3. Loop.prepareMainLooper,

4. 创建系统Context  createSystemContext

5. 启动系统的各种服务，包括AMS。startBootstrapServices() startCoreServices() startOtherServices()

6. Looper.Loop();

private void run() {        try {
            ......            
            // the property. http://b/11463182
            SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());            // Mmmmmm... more memory!
            VMRuntime.getRuntime().clearGrowthLimit();            // The system server has to run all of the time, so it needs to be
            // as efficient as possible with its memory usage.
            VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);

            ...... 
            // Ensure binder calls into the system always run at foreground priority.
            BinderInternal.disableBackgroundScheduling(true);            // Increase the number of binder threads in system_server
            BinderInternal.setMaxThreads(sMaxBinderThreads);            // Prepare the main looper thread (this thread).
            android.os.Process.setThreadPriority(
                android.os.Process.THREAD_PRIORITY_FOREGROUND);
            android.os.Process.setCanSelfBackground(false);
            Looper.prepareMainLooper();
            Looper.getMainLooper().setSlowLogThresholdMs(
                    SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);            // Initialize native services.
            System.loadLibrary("android_servers");            // Initialize the system context.
            createSystemContext();

        } finally {
        }        // Start services.
        try {
            traceBeginAndSlog("StartServices");
            startBootstrapServices();
            startCoreServices();
            startOtherServices();
            SystemServerInitThreadPool.shutdown();
        } catch (Throwable ex) {

        } finally {
            traceEnd();
        }

        StrictMode.initVmDefaults(null);       
        // Loop forever.
        Looper.loop();        throw new RuntimeException("Main thread loop unexpectedly exited");
    }

三 AMS 运行

1. SystemServer#startBootstrapServices 通过mSystemServiceManager 启动ActivityManagerService。

2. 启动ActivityManagerService

3.1 mSystemServiceManager.startService

private void startBootstrapServices() {       
        // Activity manager runs the show.
        mActivityManagerService = mSystemServiceManager.startService(
                ActivityManagerService.Lifecycle.class).getService();
        mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
       
        mActivityManagerService.setSystemProcess();

3.2 启动ActivityManagerService

ActivityManagerService 准备工作线程，
准备Android 四大组件相关的数据结构，

public ActivityManagerService(Context systemContext) 
        mContext = systemCotex

        mSystemThread = ActivityThread.currentActivityThread();
        mUiContext = mSystemThread.getSystemUiContext();

        mHandlerThread = new ServiceThread(TAG,
                THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
        mHandlerThread.start();
        mHandler = new MainHandler(mHandlerThread.getLooper());
        mUiHandler = mInjector.getUiHandler(this);


        mFgBroadcastQueue = new BroadcastQueue(this, mHandler,                "foreground", BROADCAST_FG_TIMEOUT, false);
        mBgBroadcastQueue = new BroadcastQueue(this, mHandle                "background", BROADCAST_BG_TIMEOUT, true);
        mBroadcastQueues[0] = mFgBroadcastQueue;
        mBroadcastQueues[1] = mBgBroadcastQueue;
        
        mServices = new ActiveServices(this);
        mProviderMap = new ProviderMap(this);
    
        mStackSupervisor = createStackSupervisor();
        mActivityStarter = new ActivityStarter(this, mStackSupervisor);
        mRecentTasks = new RecentTasks(this, mStackSupervisor);
    }

3.3 AMS  setSystemProcess()

AMS 通过 setSystemProcess 把System_Server 进程加入到AMS 的进程管理中。加载 framework-res.apk

public void setSystemProcess() {        try {
            ServiceManager.addService(Context.ACTIVITY_SERVICE, this, /* allowIsolated= */ true,
                    DUMP_FLAG_PRIORITY_CRITICAL | DUMP_FLAG_PRIORITY_NORMAL | DUMP_FLAG_PROTO);
            ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
            ServiceManager.addService("meminfo", new MemBinder(this), /* allowIsolated= */ false,
                    DUMP_FLAG_PRIORITY_HIGH);
            ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
            ServiceManager.addService("dbinfo", new DbBinder(this));
            ServiceManager.addService("permission", new PermissionController(this));
            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) {
                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();
            }
        } catch (PackageManager.NameNotFoundException e) {            throw new RuntimeException(                    "Unable to find android system package", e);
        }
    }

3.4  installSystemProviders

在中startOtherServices 安装 SettingProvider

mActivityManagerService.installSystemProviders();

3.5  setWindowManager

mActivityManagerService.setWindowManager(wm);

3.6 systemReady

各种服务启动完毕后，systemReady. 在systemReady 中先启动SystemUI, 然后启动Launcher.

作者：赤兔欢
链接：https://www.jianshu.com/p/1a95acaa6bff