SystemServer的启动-阿里云开发者社区

frameworks\base\core\java\com\android\internal\os\ZygoteInit.java的forkSystemServer

   /* Request to fork the system server process */
            pid = Zygote.forkSystemServer(
                    parsedArgs.mUid, parsedArgs.mGid,
                    parsedArgs.mGids,
                    parsedArgs.mRuntimeFlags,
                    null,
                    parsedArgs.mPermittedCapabilities,
                    parsedArgs.mEffectiveCapabilities);
        } catch (IllegalArgumentException ex) {
            throw new RuntimeException(ex);
        }
 
        /* For child process */
        if (pid == 0) {
            if (hasSecondZygote(abiList)) {
                waitForSecondaryZygote(socketName);
            }
 
            zygoteServer.closeServerSocket();
            return handleSystemServerProcess(parsedArgs);
        }

handleSystemServerProcess来启动SyetemServer进程。

handleSystemServerProcess关键代码

/*
             * Pass the remaining arguments to SystemServer.
             */
            return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
                    parsedArgs.mDisabledCompatChanges,
                    parsedArgs.mRemainingArgs, cl);

    public static final Runnable zygoteInit(int targetSdkVersion, long[] disabledCompatChanges,
            String[] argv, ClassLoader classLoader) {
        if (RuntimeInit.DEBUG) {
            Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
        }
 
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
        RuntimeInit.redirectLogStreams();
 
        RuntimeInit.commonInit();
        ZygoteInit.nativeZygoteInit();
        return RuntimeInit.applicationInit(targetSdkVersion, disabledCompatChanges, argv,
                classLoader);
    }

nativeZygoteInit方法在 frameworks/base/core/jni/AndroidRuntime.cpp中定义

int register_com_android_internal_os_ZygoteInit_nativeZygoteInit(JNIEnv* env)
{
    const JNINativeMethod methods[] = {
        { "nativeZygoteInit", "()V",
            (void*) com_android_internal_os_ZygoteInit_nativeZygoteInit },
    };
    return jniRegisterNativeMethods(env, "com/android/internal/os/ZygoteInit",
        methods, NELEM(methods));
}

对应的方法为com_android_internal_os_ZygoteInit_nativeZygoteInit

static void com_android_internal_os_ZygoteInit_nativeZygoteInit(JNIEnv* env, jobject clazz)
{
    gCurRuntime->onZygoteInit();
}

这里gCurRuntime是AndroidRuntime类型的指针，AndroidRuntime的子类AppRuntime在app_main.cpp中定义，我们来查看AppRuntime的onZygoteInit函数，代码如下所示。

frameworks\base\cmds\app_process\app_main.cpp

 virtual void onZygoteInit()
    {
        sp<ProcessState> proc = ProcessState::self();
        ALOGV("App process: starting thread pool.\n");
        //启动一个Binder线程池，这样SyetemServer进程就可以使用Binder来与其他进程进行通信了
        proc->startThreadPool();
    }

applicationInit在frameworks\base\core\java\com\android\internal\os\RuntimeInit.java中

 protected static Runnable applicationInit(int targetSdkVersion, long[] disabledCompatChanges,
            String[] argv, ClassLoader classLoader) {
        // If the application calls System.exit(), terminate the process
        // immediately without running any shutdown hooks.  It is not possible to
        // shutdown an Android application gracefully.  Among other things, the
        // Android runtime shutdown hooks close the Binder driver, which can cause
        // leftover running threads to crash before the process actually exits.
        nativeSetExitWithoutCleanup(true);
 
        VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
        VMRuntime.getRuntime().setDisabledCompatChanges(disabledCompatChanges);
 
        final Arguments args = new Arguments(argv);
 
        // The end of of the RuntimeInit event (see #zygoteInit).
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
 
        // Remaining arguments are passed to the start class's static main
        return findStaticMain(args.startClass, args.startArgs, classLoader);
    }

findStaticMain方法主要调用了MethodAndArgsCaller(m, argv);

protected static Runnable findStaticMain(String className, String[] argv,
            ClassLoader classLoader) {
        Class<?> cl;
 
        try {
            cl = Class.forName(className, true, classLoader);
        } catch (ClassNotFoundException ex) {
            throw new RuntimeException(
                    "Missing class when invoking static main " + className,
                    ex);
        }
 
        Method m;
        try {
            m = cl.getMethod("main", new Class[] { String[].class });
        } catch (NoSuchMethodException ex) {
            throw new RuntimeException(
                    "Missing static main on " + className, ex);
        } catch (SecurityException ex) {
            throw new RuntimeException(
                    "Problem getting static main on " + className, ex);
        }
 
        int modifiers = m.getModifiers();
        if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
            throw new RuntimeException(
                    "Main method is not public and static on " + className);
        }
 
        /*
         * This throw gets caught in ZygoteInit.main(), which responds
         * by invoking the exception's run() method. This arrangement
         * clears up all the stack frames that were required in setting
         * up the process.
         */
        return new MethodAndArgsCaller(m, argv);
    }

MethodAndArgsCaller的run方法调用

mMethod.invoke(null, new Object[] { mArgs });

SystemServer的main函数被动态调用。

进入SystemServer

frameworks\base\services\java\com\android\server\SystemServer.java

 public static void main(String[] args) {
        new SystemServer().run();
    }

run方法关键代码如下

System.loadLibrary("android_servers");加载了libandroid_servers.so
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);创建SystemServiceManager，它会对系统的服务进行创建、启动和生命周期管理
 
startBootstrapServices(t);
startCoreServices(t);
startOtherServices(t);

BootstrapServices	作用
Installer	系统安装apk时的一个服务类，启动完成Installer服务之后才能启动其他的系统服务
ActivityManagerService	负责四大组件的启动、切换、调度。
PowerManagerService	计算系统中和Power相关的计算，然后决策系统应该如何反应
LightsService	管理和显示背光LED
DisplayManagerService	用来管理所有显示设备
UserManagerService	多用户模式管理
SensorService	为系统提供各种感应器服务
PackageManagerService	用来对apk进行安装、解析、删除、卸载等等操作
CoreServices
BatteryService	管理电池相关的服务
UsageStatsService	收集用户使用每一个APP的频率、使用时常
WebViewUpdateService	WebView更新服务
OtherServices
CameraService	摄像头相关服务
AlarmManagerService	全局定时器管理服务
InputManagerService	管理输入事件
WindowManagerService	窗口管理服务
VrManagerService	VR模式管理服务
BluetoothService	蓝牙管理服务
NotificationManagerService	通知管理服务
DeviceStorageMonitorService	存储相关管理服务
LocationManagerService	定位管理服务
AudioService	音频相关管理服务
…	….

显示详细信息

要启动那个服务，调用SystemServiceManager的startService方法即可

mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);

frameworks\base\services\core\java\com\android\server\SystemServiceManager.java

    public SystemService startService(String className) {
        final Class<SystemService> serviceClass = loadClassFromLoader(className,
                this.getClass().getClassLoader());
        return startService(serviceClass);
    }

    public <T extends SystemService> T startService(Class<T> serviceClass) {
        try {
            final String name = serviceClass.getName();
            Slog.i(TAG, "Starting " + name);
            Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartService " + name);
 
            // Create the service.
            if (!SystemService.class.isAssignableFrom(serviceClass)) {
                throw new RuntimeException("Failed to create " + name
                        + ": service must extend " + SystemService.class.getName());
            }
            final T service;
            try {
                Constructor<T> constructor = serviceClass.getConstructor(Context.class);
                service = constructor.newInstance(mContext);创建service实例
            } catch (InstantiationException ex) {
                throw new RuntimeException("Failed to create service " + name
                        + ": service could not be instantiated", ex);
            } catch (IllegalAccessException ex) {
                throw new RuntimeException("Failed to create service " + name
                        + ": service must have a public constructor with a Context argument", ex);
            } catch (NoSuchMethodException ex) {
                throw new RuntimeException("Failed to create service " + name
                        + ": service must have a public constructor with a Context argument", ex);
            } catch (InvocationTargetException ex) {
                throw new RuntimeException("Failed to create service " + name
                        + ": service constructor threw an exception", ex);
            }
 
            startService(service);
            return service;
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
        }
    }
 
    public void startService(@NonNull final SystemService service) {
        // Register it.
        mServices.add(service);
        // Start it.
        long time = SystemClock.elapsedRealtime();
        try {
            service.onStart();
        } catch (RuntimeException ex) {
            throw new RuntimeException("Failed to start service " + service.getClass().getName()
                    + ": onStart threw an exception", ex);
        }
        warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");
    }

总结SyetemServer进程

SyetemServer在启动时做了如下工作：

1.启动Binder线程池，这样就可以与其他进程进行通信。

2.创建SystemServiceManager用于对系统的服务进行创建、启动和生命周期管理。

3.启动各种系统服务。

SystemServer的启动

进入SystemServer

总结SyetemServer进程

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