Android Input输入子系统分析

最开始接触android系统便是touch驱动，属于典型的input输入子系统设备，但是从未认真总结过，蓦然回首，总结一下：

input输入子系统是对一些输入设备的总体规划，标准的接口，外设中诸如键盘，鼠标，触摸屏等都是典型的input设备，这些设备的事件处理都是走input输入子系统流程，而input系统在底层有相应的驱动，在上层有相应的守护server，首先看InputManagerService的启动：

            inputManager = new InputManagerService(context, wmHandler);            Slog.i(TAG, "Window Manager");            wm = WindowManagerService.main(context, power, display, inputManager,                    wmHandler, factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL,                    !firstBoot, onlyCore);            ServiceManager.addService(Context.WINDOW_SERVICE, wm);            ServiceManager.addService(Context.INPUT_SERVICE, inputManager);            ActivityManagerService.self().setWindowManager(wm);            inputManager.setWindowManagerCallbacks(wm.getInputMonitor());            inputManager.start();

首行便是初始化一个InputManagerService的实例，

public InputManagerService(Context context, Handler handler) {        this.mContext = context;        this.mHandler = new InputManagerHandler(handler.getLooper());        mUseDevInputEventForAudioJack =                context.getResources().getBoolean(R.bool.config_useDevInputEventForAudioJack);        Slog.i(TAG, "Initializing input manager, mUseDevInputEventForAudioJack="                + mUseDevInputEventForAudioJack);        mPtr = nativeInit(this, mContext, mHandler.getLooper().getQueue());    }

nativeInit方法：

static jint nativeInit(JNIEnv* env, jclass clazz,        jobject serviceObj, jobject contextObj, jobject messageQueueObj) {    sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);    if (messageQueue == NULL) {        jniThrowRuntimeException(env, "MessageQueue is not initialized.");        return 0;    }    NativeInputManager* im = new NativeInputManager(contextObj, serviceObj,            messageQueue->getLooper());    im->incStrong(0);    return reinterpret_cast<jint>(im);}

代码段如下：

NativeInputManager::NativeInputManager(jobject contextObj,        jobject serviceObj, const sp<Looper>& looper) :        mLooper(looper) {    JNIEnv* env = jniEnv();    mContextObj = env->NewGlobalRef(contextObj);    mServiceObj = env->NewGlobalRef(serviceObj);    {        AutoMutex _l(mLock);        mLocked.systemUiVisibility = ASYSTEM_UI_VISIBILITY_STATUS_BAR_VISIBLE;        mLocked.pointerSpeed = 0;        mLocked.pointerGesturesEnabled = true;        mLocked.showTouches = false;    }    sp<EventHub> eventHub = new EventHub();    mInputManager = new InputManager(eventHub, this, this);}

初始化InputManager实例；

InputManager::InputManager(        const sp<EventHubInterface>& eventHub,        const sp<InputReaderPolicyInterface>& readerPolicy,        const sp<InputDispatcherPolicyInterface>& dispatcherPolicy) {    mDispatcher = new InputDispatcher(dispatcherPolicy);    mReader = new InputReader(eventHub, readerPolicy, mDispatcher);#ifdef USE_POWER_HINT_INPUT_BOOST    mMonitor = new PhsInputMonitor(eventHub, readerPolicy);#endif    initialize();}

initialize()方法，初始化两个线程，InputReader和InputDispatcher等，

void InputManager::initialize() {    mReaderThread = new InputReaderThread(mReader);    mDispatcherThread = new InputDispatcherThread(mDispatcher);}

回到一开始的代码段的紫色行，代码调用了inputManager的start（）方法：

public void start() {        Slog.i(TAG, "Starting input manager");        nativeStart(mPtr);        // Add ourself to the Watchdog monitors.        Watchdog.getInstance().addMonitor(this);        registerPointerSpeedSettingObserver();        registerShowTouchesSettingObserver();        mContext.registerReceiver(new BroadcastReceiver() {            @Override            public void onReceive(Context context, Intent intent) {                updatePointerSpeedFromSettings();                updateShowTouchesFromSettings();            }        }, new IntentFilter(Intent.ACTION_USER_SWITCHED), null, mHandler);        updatePointerSpeedFromSettings();        updateShowTouchesFromSettings();    }

红色标注的代码段是关键，

static void nativeStart(JNIEnv* env, jclass clazz, jint ptr) {    NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);    status_t result = im->getInputManager()->start();    if (result) {        jniThrowRuntimeException(env, "Input manager could not be started.");    }}

调用至InputManager的start（）方法；

status_t InputManager::start() {    status_t result = mDispatcherThread->run("InputDispatcher", PRIORITY_URGENT_DISPLAY);    if (result) {        ALOGE("Could not start InputDispatcher thread due to error %d.", result);        return result;    }    result = mReaderThread->run("InputReader", PRIORITY_URGENT_DISPLAY);    if (result) {        ALOGE("Could not start InputReader thread due to error %d.", result);        mDispatcherThread->requestExit();        return result;    }#ifdef USE_POWER_HINT_INPUT_BOOST    mMonitor->startMonitor();#endif    return OK;}

末段，开启了上边提到的两个关键线程，mDispatcherThread和mReaderThread，后面继续分析input子系统在上层的这两个关键线程：大体流程就是ReaderThread通过EventHub获取kernel上报的input事件，唤醒DispatherThread去处理相关input事件，Dispatcher根据事件的类型以及有效性做一个判断，从而决定事件发送不发送，发送给谁等。详细的方法调用流程，后面的文章会做分析。。。先告一段落！