BAT软件工程师带你深入理解AMS --- 一 AMS 的启动

一 Zygote fork
Zygote fork SystemServer 的过程如下:

ZygoteInit#forkSystemServer

ZygoteInit#handleSystemServerProcess

ZygoteInit#zygoteInit

RuntimeInit#applicationInit

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
开始首先配置 VM 参数

Binder 参数,

Loop.prepareMainLooper,

创建系统Context createSystemContext

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

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
SystemServer#startBootstrapServices 通过mSystemServiceManager 启动ActivityManagerService。

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.

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