Android输入输出机制之来龙去脉之前生后世

void TouchInputMapper::dispatchTouches(nsecs_t when, uint32_t policyFlags) {
// Dispatch pointer down events using the new pointer locations.
while (!downIdBits.isEmpty()) {
dispatchTouch(when, policyFlags, &mCurrentTouch,
activeIdBits, downId, pointerCount, motionEventAction);
}
}
}

dispatchTouch(when, policyFlags, &mCurrentTouch,
activeIdBits, downId, pointerCount, motionEventAction);

这个方法展开如下：

void TouchInputMapper::dispatchTouch(nsecs_t when, uint32_t policyFlags,
TouchData* touch, BitSet32 idBits, uint32_t changedId, uint32_t pointerCount,
int32_t motionEventAction) {
int32_t pointerIds[MAX_POINTERS];
PointerCoords pointerCoords[MAX_POINTERS];
int32_t motionEventEdgeFlags = 0;
float xPrecision, yPrecision;
{ 
getDispatcher()->notifyMotion(when, getDeviceId(), getSources(), policyFlags,
motionEventAction, 0, getContext()->getGlobalMetaState(), motionEventEdgeFlags,
pointerCount, pointerIds, pointerCoords,
xPrecision, yPrecision, mDownTime);
}

  这样就到了InputDiaptcher的notifyMotion方法，这个方法很长，都再处理MOVE事件，将无用的删除后，留下如下关键代码：

 void InputDispatcher::notifyMotion(nsecs_t eventTime, int32_t deviceId, int32_t source,
uint32_t policyFlags, int32_t action, int32_t flags, int32_t metaState, int32_t edgeFlags,
uint32_t pointerCount, const int32_t* pointerIds, const PointerCoords* pointerCoords,
float xPrecision, float yPrecision, nsecs_t downTime) {      
// Just enqueue a new motion event.
MotionEntry* newEntry = mAllocator.obtainMotionEntry(eventTime,
deviceId, source, policyFlags, action, flags, metaState, edgeFlags,
xPrecision, yPrecision, downTime,
pointerCount, pointerIds, pointerCoords);
needWake = enqueueInboundEventLocked(newEntry);
}

 最后一句：

 needWake = enqueueInboundEventLocked(newEntry);

bool InputDispatcher::enqueueInboundEventLocked(EventEntry* entry) {
bool needWake = mInboundQueue.isEmpty();
mInboundQueue.enqueueAtTail(entry);
switch (entry->type) {
case EventEntry::TYPE_KEY: {
KeyEntry* keyEntry = static_cast<KeyEntry*>(entry);
if (isAppSwitchKeyEventLocked(keyEntry)) {
if (keyEntry->action == AKEY_EVENT_ACTION_DOWN) {
mAppSwitchSawKeyDown = true;
} else if (keyEntry->action == AKEY_EVENT_ACTION_UP) {
if (mAppSwitchSawKeyDown) {
#if DEBUG_APP_SWITCH
LOGD("App switch is pending!");
#endif
mAppSwitchDueTime = keyEntry->eventTime + APP_SWITCH_TIMEOUT;
mAppSwitchSawKeyDown = false;
needWake = true;
}
}
}
break;
}
}
return needWake;
}

mInboundQueue正是上面所说的队列。到此为止，从InputReader插入到队列就完成了。

 那么InputDispatcher又是如何从队列中取出来的呢？累了。

  InputDiapather的

dispatchOnce

方法如下：

void InputDispatcher::dispatchOnce() {
nsecs_t keyRepeatTimeout = mPolicy->getKeyRepeatTimeout();
nsecs_t keyRepeatDelay = mPolicy->getKeyRepeatDelay();
nsecs_t nextWakeupTime = LONG_LONG_MAX;
{ // acquire lock
AutoMutex _l(mLock);
dispatchOnceInnerLocked(keyRepeatTimeout, keyRepeatDelay, & nextWakeupTime);
if (runCommandsLockedInterruptible()) {
nextWakeupTime = LONG_LONG_MIN;  // force next poll to wake up immediately
}
} // release lock
// Wait for callback or timeout or wake.  (make sure we round up, not down)
nsecs_t currentTime = now();
int32_t timeoutMillis;
if (nextWakeupTime > currentTime) {
uint64_t timeout = uint64_t(nextWakeupTime - currentTime);
timeout = (timeout + 999999LL) / 1000000LL;
timeoutMillis = timeout > INT_MAX ? -1 : int32_t(timeout);
} else {
timeoutMillis = 0;
}
mLooper->pollOnce(timeoutMillis);
}

 最关键的是

  dispatchOnceInnerLocked(keyRepeatTimeout, keyRepeatDelay, & nextWakeupTime);

和

    mLooper->pollOnce(timeoutMillis);（这个方法在有个回调，与事件有关的是【管道设备的文件描述符】。
具体机制在后面讲。这个东西实际上是个跨进程的信号。发送给了Android的用户进程的JNI，又通过JNI调用InputQueue的的
静态方法如：dispatchMotionEvent。后面回提到dispatchMotionEvent才是Android用户进程的事件入口函数。）
）

代码又长又臭

void InputDispatcher::dispatchOnceInnerLocked(nsecs_t keyRepeatTimeout,
nsecs_t keyRepeatDelay, nsecs_t* nextWakeupTime) {
case EventEntry::TYPE_MOTION: {
MotionEntry* typedEntry = static_cast<MotionEntry*>(mPendingEvent);
if (dropReason == DROP_REASON_NOT_DROPPED && isAppSwitchDue) {
dropReason = DROP_REASON_APP_SWITCH;
}
done = dispatchMotionLocked(currentTime, typedEntry,
&dropReason, nextWakeupTime);
break;
}
}

dispatchMotionLocked

方法调用prepareDispatchCycleLocked，调用startDispatchCycleLocked，最终调用

       // Publish the key event.
        status = connection->inputPublisher.publishKeyEvent(keyEntry->deviceId, keyEntry->source,
                action, flags, keyEntry->keyCode, keyEntry->scanCode,
                keyEntry->metaState, keyEntry->repeatCount, keyEntry->downTime,
                keyEntry->eventTime);

或者 // Publish the motion event and the first motion sample.
        status = connection->inputPublisher.publishMotionEvent(motionEntry->deviceId,
                motionEntry->source, action, flags, motionEntry->edgeFlags, motionEntry->metaState,
                xOffset, yOffset,
                motionEntry->xPrecision, motionEntry->yPrecision,
                motionEntry->downTime, firstMotionSample->eventTime,
                motionEntry->pointerCount, motionEntry->pointerIds,
                firstMotionSample->pointerCoords);

至此，InputDisapatcher也结束了。

既然发布出去，必然有订阅者：在InputTransport.cpp中

status_t InputConsumer::consume(InputEventFactoryInterface* factory, InputEvent** outEvent) {
#if DEBUG_TRANSPORT_ACTIONS
LOGD("channel '%s' consumer ~ consume",
mChannel->getName().string());
#endif
*outEvent = NULL;
int ashmemFd = mChannel->getAshmemFd();
int result = ashmem_pin_region(ashmemFd, 0, 0);
if (result != ASHMEM_NOT_PURGED) {
if (result == ASHMEM_WAS_PURGED) {
LOGE("channel '%s' consumer ~ Error %d pinning ashmem fd %d because it was purged "
"which probably indicates that the publisher and consumer are out of sync.",
mChannel->getName().string(), result, ashmemFd);
return INVALID_OPERATION;
}
LOGE("channel '%s' consumer ~ Error %d pinning ashmem fd %d.",
mChannel->getName().string(), result, ashmemFd);
return UNKNOWN_ERROR;
}
if (mSharedMessage->consumed) {
LOGE("channel '%s' consumer ~ The current message has already been consumed.",
mChannel->getName().string());
return INVALID_OPERATION;
}
// Acquire but *never release* the semaphore.  Contention on the semaphore is used to signal
// to the publisher that the message has been consumed (or is in the process of being
// consumed).  Eventually the publisher will reinitialize the semaphore for the next message.
result = sem_wait(& mSharedMessage->semaphore);
if (result < 0) {
LOGE("channel '%s' consumer ~ Error %d in sem_wait.",
mChannel->getName().string(), errno);
return UNKNOWN_ERROR;
}
mSharedMessage->consumed = true;
switch (mSharedMessage->type) {
case AINPUT_EVENT_TYPE_KEY: {
KeyEvent* keyEvent = factory->createKeyEvent();
if (! keyEvent) return NO_MEMORY;
populateKeyEvent(keyEvent);
*outEvent = keyEvent;
break;
}
case AINPUT_EVENT_TYPE_MOTION: {
MotionEvent* motionEvent = factory->createMotionEvent();
if (! motionEvent) return NO_MEMORY;
populateMotionEvent(motionEvent);
*outEvent = motionEvent;
break;
}
default:
LOGE("channel '%s' consumer ~ Received message of unknown type %d",
mChannel->getName().string(), mSharedMessage->type);
return UNKNOWN_ERROR;
}
return OK;
}

 也许我们最关心的是如何订阅的，不得不取看一下JNI的代码，文件android_view_InputQueue.cpp

 聚焦到这里

status_t NativeInputQueue::registerInputChannel(JNIEnv* env, jobject inputChannelObj,
jobject inputHandlerObj, jobject messageQueueObj) {
sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
inputChannelObj);
if (inputChannel == NULL) {
LOGW("Input channel is not initialized.");
return BAD_VALUE;
}
#if DEBUG_REGISTRATION
LOGD("channel '%s' - Registered", inputChannel->getName().string());
#endif
sp<Looper> looper = android_os_MessageQueue_getLooper(env, messageQueueObj);
{ // acquire lock
AutoMutex _l(mLock);
if (getConnectionIndex(inputChannel) >= 0) {
LOGW("Attempted to register already registered input channel '%s'",
inputChannel->getName().string());
return BAD_VALUE;
}
uint16_t connectionId = mNextConnectionId++;
sp<Connection> connection = new Connection(connectionId, inputChannel, looper);
status_t result = connection->inputConsumer.initialize();
if (result) {
LOGW("Failed to initialize input consumer for input channel '%s', status=%d",
inputChannel->getName().string(), result);
return result;
}
connection->inputHandlerObjGlobal = env->NewGlobalRef(inputHandlerObj);
int32_t receiveFd = inputChannel->getReceivePipeFd();
mConnectionsByReceiveFd.add(receiveFd, connection);
looper->addFd(receiveFd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);
} // release lock
android_view_InputChannel_setDisposeCallback(env, inputChannelObj,
handleInputChannelDisposed, this);
return OK;
}

  也许更想知道的是消息队列在什么地方，进入InputQueue.java来看

    public static void registerInputChannel(InputChannel inputChannel, InputHandler inputHandler,
MessageQueue messageQueue) {
if (inputChannel == null) {
throw new IllegalArgumentException("inputChannel must not be null");
}
if (inputHandler == null) {
throw new IllegalArgumentException("inputHandler must not be null");
}
if (messageQueue == null) {
throw new IllegalArgumentException("messageQueue must not be null");
}
synchronized (sLock) {
if (DEBUG) {
Slog.d(TAG, "Registering input channel '" + inputChannel + "'");
}
nativeRegisterInputChannel(inputChannel, inputHandler, messageQueue);
}
}

在ViewRoot.java中有这么几行

                    InputQueue.registerInputChannel(mInputChannel, mInputHandler,
Looper.myQueue());

 完毕。

这才牵涉到管道的问题，哪个Java中的Channel对应的正是linux系统的管道。有了管道，才能通过 跨进程方式回调回来，为什么是这个入口，上面进行了解释。具体参照INputQUEUE这个java类的JNI方法

int NativeInputQueue::handleReceiveCallback(int receiveFd, int events, void* data)

这个方法被InputQueue的RegisterInputChannel注册给了系统.系统通过回调，回调的是这个ALOOPER_EVENT_INPUT事件。

looper就是android中的【用户进程的循环】

注册的代码为 ：

  looper->addFd(receiveFd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);

回调的java函数为

    
回调的java代码的方法入口为：InputQueue.java中的。
@SuppressWarnings("unused")
private static void dispatchMotionEvent(InputHandler inputHandler,
MotionEvent event, long finishedToken) {
Runnable finishedCallback = FinishedCallback.obtain(finishedToken);
inputHandler.handleMotion(event, finishedCallback);
}

 这样就回调到了ViewRoot中