Android Input流程分析（一）：启动

  Java层的InputManagerService由System Server启动。
/frameworks/base/services/java/com/android/server/SystemServer.java

        Slog.i(TAG, "Input Manager");
        inputManager = new InputManagerService(context);

  重点关注nativeInit方法。
/frameworks/base/services/core/java/com/android/server/input/InputManagerService.java

public InputManagerService(Context context) {
        this.mContext = context;
        this.mHandler = new InputManagerHandler(DisplayThread.get().getLooper());

        mUseDevInputEventForAudioJack =
                context.getResources().getBoolean(R.bool.config_useDevInputEventForAudioJack);
        Slog.i(TAG, "Initializing input manager, mUseDevInputEventForAudioJack="
                + mUseDevInputEventForAudioJack);
        mPtr = nativeInit(this, mContext, mHandler.getLooper().getQueue());

        LocalServices.addService(InputManagerInternal.class, new LocalService());
    }

  nativeInit最终会调到JNI层的nativeInit函数。android_os_MessageQueue_getMessageQueue获得一个Native层的MessgaeQueue引用。之后new了一个NativeInputManager对象，返回NativeInputManager的指针保存在Java层的mPtr中。
/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp

static jlong nativeInit(JNIEnv* env, jclass /* clazz */,
        jobject serviceObj, jobject contextObj, jobject messageQueueObj) {
    sp 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(im);
}

  NativeInputManager的构造函数里new了一个EventHub和一个InputManager，EventHub用来收集底层传上来的Input事件，InputManager用来创建InputDispatcher和InputReader。
/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp

NativeInputManager::NativeInputManager(jobject contextObj,
        jobject serviceObj, const sp& looper) :
        mLooper(looper), mInteractive(true) {
    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;
    }
    mInteractive = true;

    sp eventHub = new EventHub();
    mInputManager = new InputManager(eventHub, this, this);
}

/frameworks/native/services/inputflinger/InputManager.cpp

InputManager::InputManager(
        const sp& eventHub,
        const sp& readerPolicy,
        const sp& dispatcherPolicy) {
    mDispatcher = new InputDispatcher(dispatcherPolicy);
    mReader = new InputReader(eventHub, readerPolicy, mDispatcher);
    initialize();
}

  initialize函数中创建了两个线程，但在哪里启动呢？
/frameworks/native/services/inputflinger/InputManager.cpp

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

  答案在SystemServer中的start函数中。
/frameworks/base/services/java/com/android/server/SystemServer.java

 inputManager.start();

  InputManagerService的start函数会使用nativeStart调到JNI层，并使用保存了native层的NativeInputManager指针作为入参。
/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp

static void nativeStart(JNIEnv* env, jclass /* clazz */, jlong ptr) {
    NativeInputManager* im = reinterpret_cast(ptr);

    status_t result = im->getInputManager()->start();
    if (result) {
        jniThrowRuntimeException(env, "Input manager could not be started.");
    }
}

  从ptr中捞出native层的NativeInputManager指针。getInputManager返回的是InputManager对象，然后调用InputManager::start分别启动InputReaderThread和InputDispatcherThread两个线程。值得指出的是，调用Thread的run函数会进入ThreadLoop循环，这个ThreadLoop循环由子类实现，返回值是取决于内部pthread_create的返回值的，而不是内部循环的返回值，所以一经调用即有返回值，为0时表示成功。requestExit表示退出ThreadLoop循环。退出ThreadLoop循环的方法有两个：1.ThreadLoop内部返回false;2.调用requestExit方法。
/frameworks/native/services/inputflinger/InputManager.cpp

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;
    }

    return OK;
}

  EventHub,InputReader和InputDispatcher的关系是：EventHub负责从内核捞起Input事件，InputReader负责加工从EventHub送过来的Input事件，InputDispatcher负责分派InputReader送来的Input事件到合适的窗口。