前言
上一篇文章中，对于事件的监控和获取做了分析，在拿到事件之后，后续是如何处理分发的呢？本篇文章主要针对在通过getEvent获取到事件之后，后续的相关分发处理流程。
InputReaderThread函数不断地调用looperOnce函数，不断的从中读取事件，那么下一个问题来了，读取到事件要放置到哪里，又在哪里被消耗掉了呢？也就是事件接下来的流向问题。让我们回到looperOnce之前。
事件分发
processEventsLocked
在调用了getEvent之后，又调用了函数processEventsLocked
void InputReader::processEventsLocked(const RawEvent* rawEvents, size_t count) {
for (const RawEvent* rawEvent = rawEvents; count;) {
int32_t type = rawEvent->type;
size_t batchSize = 1;
if (type < EventHubInterface::FIRST_SYNTHETIC_EVENT) {
int32_t deviceId = rawEvent->deviceId;
while (batchSize < count) {
if (rawEvent[batchSize].type >= EventHubInterface::FIRST_SYNTHETIC_EVENT
|| rawEvent[batchSize].deviceId != deviceId) {
break;
}
batchSize += 1;
}
processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
} else {
switch (rawEvent->type) {
case EventHubInterface::DEVICE_ADDED:
addDeviceLocked(rawEvent->when, rawEvent->deviceId);
break;
case EventHubInterface::DEVICE_REMOVED:
removeDeviceLocked(rawEvent->when, rawEvent->deviceId);
break;
case EventHubInterface::FINISHED_DEVICE_SCAN:
handleConfigurationChangedLocked(rawEvent->when);
break;
default:
ALOG_ASSERT(false); // can't happen
break;
}
}
count -= batchSize;
rawEvent += batchSize;
}
}首先对于事件类型进行了判断，如果事件不是合成事件，则会对其DeviceID进行判断，通过对其判断来确定batchSize等，然后对其进行处理，对于其他的类型事件，则会具体判断，判断是设备的添加，设备的移除，完成设备扫描等等，然后对事件分别进行处理，这里我们只关心对于设备自身产生的事件。也就是触摸屏相关的事件。也就是processEventsForDeviceLocked函数中所进行的操作。
事件派发到Device
void InputReader::processEventsForDeviceLocked(int32_t deviceId,
const RawEvent* rawEvents, size_t count) {
ssize_t deviceIndex = mDevices.indexOfKey(deviceId);
if (deviceIndex < 0) {
return;
}
InputDevice* device = mDevices.valueAt(deviceIndex);
if (device->isIgnored()) {
return;
}
device->process(rawEvents, count);
}根据事件获得相应的设备类型，然后将事件交给相应的设备处理。判断是否忽略该事件，如果不是忽略该事件，则会调用相应设备的process方法进行处理。
事件派发到InputMapper
InputDevice的process方法
void InputDevice::process(const RawEvent* rawEvents, size_t count) {
....
for (size_t i = 0; i < numMappers; i++) {
InputMapper* mapper = mMappers[i];
mapper->process(rawEvent);
}
....
}这里的事件又交给了InputMapper来处理
InputMapper对应了很多的子类，这里根据事件的类型进行相应的派发，处理。
事件到了这里之后，如何传递到应用层，这里mapper->process进行了那些处理。这里来看一下对于触摸屏事件的处理函数。
void TouchInputMapper::process(const RawEvent* rawEvent) {
mCursorButtonAccumulator.process(rawEvent);
mCursorScrollAccumulator.process(rawEvent);
mTouchButtonAccumulator.process(rawEvent);
if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {
sync(rawEvent->when);
}
}通过这里的函数处理，我们继续追踪函数的数据流向。对于相关的事件处理，这里最终执行的是将
void TouchInputMapper::sync(nsecs_t when) {
.....
processRawTouches(false /*timeout*/);
}
void TouchInputMapper::processRawTouches(bool timeout) {
if (mDeviceMode == DEVICE_MODE_DISABLED) {
// Drop all input if the device is disabled.
mCurrentRawState.clear();
mRawStatesPending.clear();
return;
}
// Drain any pending touch states. The invariant here is that the mCurrentRawState is always
// valid and must go through the full cook and dispatch cycle. This ensures that anything
// touching the current state will only observe the events that have been dispatched to the
// rest of the pipeline.
const size_t N = mRawStatesPending.size();
size_t count;
for(count = 0; count < N; count++) {
const RawState& next = mRawStatesPending[count];
// A failure to assign the stylus id means that we're waiting on stylus data
// and so should defer the rest of the pipeline.
if (assignExternalStylusId(next, timeout)) {
break;
}
// All ready to go.
clearStylusDataPendingFlags();
mCurrentRawState.copyFrom(next);
if (mCurrentRawState.when < mLastRawState.when) {
mCurrentRawState.when = mLastRawState.when;
}
cookAndDispatch(mCurrentRawState.when);
}
if (count != 0) {
mRawStatesPending.removeItemsAt(0, count);
}
if (mExternalStylusDataPending) {
if (timeout) {
nsecs_t when = mExternalStylusFusionTimeout - STYLUS_DATA_LATENCY;
clearStylusDataPendingFlags();
mCurrentRawState.copyFrom(mLastRawState);
cookAndDispatch(when);
} else if (mExternalStylusFusionTimeout == LLONG_MAX) {
mExternalStylusFusionTimeout = mExternalStylusState.when + TOUCH_DATA_TIMEOUT;
getContext()->requestTimeoutAtTime(mExternalStylusFusionTimeout);
}
}
}在相关的函数调用之后，最终调用了dispatchTouches
void TouchInputMapper::cookAndDispatch(nsecs_t when) {
// Always start with a clean state.
mCurrentCookedState.clear();
// Apply stylus buttons to current raw state.
applyExternalStylusButtonState(when);
// Handle policy on initial down or hover events.
bool initialDown = mLastRawState.rawPointerData.pointerCount == 0
&& mCurrentRawState.rawPointerData.pointerCount != 0;
uint32_t policyFlags = 0;
bool buttonsPressed = mCurrentRawState.buttonState & ~mLastRawState.buttonState;
if (initialDown || buttonsPressed) {
// If this is a touch screen, hide the pointer on an initial down.
if (mDeviceMode == DEVICE_MODE_DIRECT) {
getContext()->fadePointer();
}
if (mParameters.wake) {
policyFlags |= POLICY_FLAG_WAKE;
}
}
// Consume raw off-screen touches before cooking pointer data.
// If touches are consumed, subsequent code will not receive any pointer data.
if (consumeRawTouches(when, policyFlags)) {
mCurrentRawState.rawPointerData.clear();
}
// Cook pointer data. This call populates the mCurrentCookedState.cookedPointerData structure
// with cooked pointer data that has the same ids and indices as the raw data.
// The following code can use either the raw or cooked data, as needed.
cookPointerData();
// Apply stylus pressure to current cooked state.
applyExternalStylusTouchState(when);
// Synthesize key down from raw buttons if needed.
synthesizeButtonKeys(getContext(), AKEY_EVENT_ACTION_DOWN, when, getDeviceId(), mSource,
policyFlags, mLastCookedState.buttonState, mCurrentCookedState.buttonState);
// Dispatch the touches either directly or by translation through a pointer on screen.
if (mDeviceMode == DEVICE_MODE_POINTER) {
for (BitSet32 idBits(mCurrentRawState.rawPointerData.touchingIdBits);
!idBits.isEmpty(); ) {
uint32_t id = idBits.clearFirstMarkedBit();
const RawPointerData::Pointer& pointer =
mCurrentRawState.rawPointerData.pointerForId(id);
if (pointer.toolType == AMOTION_EVENT_TOOL_TYPE_STYLUS
|| pointer.toolType == AMOTION_EVENT_TOOL_TYPE_ERASER) {
mCurrentCookedState.stylusIdBits.markBit(id);
} else if (pointer.toolType == AMOTION_EVENT_TOOL_TYPE_FINGER
|| pointer.toolType == AMOTION_EVENT_TOOL_TYPE_UNKNOWN) {
mCurrentCookedState.fingerIdBits.markBit(id);
} else if (pointer.toolType == AMOTION_EVENT_TOOL_TYPE_MOUSE) {
mCurrentCookedState.mouseIdBits.markBit(id);
}
}
for (BitSet32 idBits(mCurrentRawState.rawPointerData.hoveringIdBits);
!idBits.isEmpty(); ) {
uint32_t id = idBits.clearFirstMarkedBit();
const RawPointerData::Pointer& pointer =
mCurrentRawState.rawPointerData.pointerForId(id);
if (pointer.toolType == AMOTION_EVENT_TOOL_TYPE_STYLUS
|| pointer.toolType == AMOTION_EVENT_TOOL_TYPE_ERASER) {
mCurrentCookedState.stylusIdBits.markBit(id);
}
}
// Stylus takes precedence over all tools, then mouse, then finger.
PointerUsage pointerUsage = mPointerUsage;
if (!mCurrentCookedState.stylusIdBits.isEmpty()) {
mCurrentCookedState.mouseIdBits.clear();
mCurrentCookedState.fingerIdBits.clear();
pointerUsage = POINTER_USAGE_STYLUS;
} else if (!mCurrentCookedState.mouseIdBits.isEmpty()) {
mCurrentCookedState.fingerIdBits.clear();
pointerUsage = POINTER_USAGE_MOUSE;
} else if (!mCurrentCookedState.fingerIdBits.isEmpty() ||
isPointerDown(mCurrentRawState.buttonState)) {
pointerUsage = POINTER_USAGE_GESTURES;
}
dispatchPointerUsage(when, policyFlags, pointerUsage);
} else {
if (mDeviceMode == DEVICE_MODE_DIRECT
&& mConfig.showTouches && mPointerController != NULL) {
mPointerController->setPresentation(PointerControllerInterface::PRESENTATION_SPOT);
mPointerController->fade(PointerControllerInterface::TRANSITION_GRADUAL);
mPointerController->setButtonState(mCurrentRawState.buttonState);
mPointerController->setSpots(mCurrentCookedState.cookedPointerData.pointerCoords,
mCurrentCookedState.cookedPointerData.idToIndex,
mCurrentCookedState.cookedPointerData.touchingIdBits);
}
if (!mCurrentMotionAborted) {
dispatchButtonRelease(when, policyFlags);
dispatchHoverExit(when, policyFlags);
dispatchTouches(when, policyFlags);
dispatchHoverEnterAndMove(when, policyFlags);
dispatchButtonPress(when, policyFlags);
}
if (mCurrentCookedState.cookedPointerData.pointerCount == 0) {
mCurrentMotionAborted = false;
}
}
// Synthesize key up from raw buttons if needed.
synthesizeButtonKeys(getContext(), AKEY_EVENT_ACTION_UP, when, getDeviceId(), mSource,
policyFlags, mLastCookedState.buttonState, mCurrentCookedState.buttonState);
// Clear some transient state.
mCurrentRawState.rawVScroll = 0;
mCurrentRawState.rawHScroll = 0;
// Copy current touch to last touch in preparation for the next cycle.
mLastRawState.copyFrom(mCurrentRawState);
mLastCookedState.copyFrom(mCurrentCookedState);
}
void TouchInputMapper::dispatchTouches(nsecs_t when, uint32_t policyFlags) {
....
dispatchMotion();
....
}对于dispatchTouches中，会根据记录的上一次的触摸位置，对事件的类型进行判断，然后做相应的分发，事件类型有抬起，下落，移动等，然后对相应的事件进行分发。无论是对于何种类型的事件派发，最终被调用到的都是dispatchMotion()方法。
对于相关事件的分发最终调用到了dispatchMotion()，对事件数据进行组装之后，调用了
void TouchInputMapper::dispatchMotion() {
....
NotifyMotionArgs args(when, getDeviceId(), source, policyFlags,
action, actionButton, flags, metaState, buttonState, edgeFlags,
mViewport.displayId, pointerCount, pointerProperties, pointerCoords,
xPrecision, yPrecision, downTime);
getListener()->notifyMotion(&args);
}getListener函数
InputListenerInterface* InputReader::ContextImpl::getListener() {
return mReader->mQueuedListener.get();
}notifyMotion函数实现
void QueuedInputListener::notifyMotion(const NotifyMotionArgs* args) {
mArgsQueue.push(new NotifyMotionArgs(*args));
}这里可以看到，我们将触摸相关的事件进行包装之后，将其加入到一个ArgsQueue队列，到此，我们已经将数据加入到参数队列中，到此事件从设备文件获取到写入流程已经完成，这里让我们再回到loopOnce方法中，最后调用了QueuedInputListener的flush方法，
void QueuedInputListener::flush() {
size_t count = mArgsQueue.size();
for (size_t i = 0; i < count; i++) {
NotifyArgs* args = mArgsQueue[i];
args->notify(mInnerListener);
delete args;
}
mArgsQueue.clear();
}NotifyArgs的notify函数实现
void NotifyMotionArgs::notify(const sp& listener) const {
listener->notifyMotion(this);
} 对于这个listener的创建来自于InputReader构建的时候。
mQueuedListener = new QueuedInputListener(listener); mReader = new InputReader(eventHub, readerPolicy, mDispatcher);而这里的Listener则是InputDispatcher，InputDispatcher 的notifyMotion实现源码。
void InputDispatcher::notifyMotion(const NotifyMotionArgs* args) {
.....
MotionEvent event;
event.initialize(args->deviceId, args->source, args->action, args->actionButton,
args->flags, args->edgeFlags, args->metaState, args->buttonState,
0, 0, args->xPrecision, args->yPrecision,
args->downTime, args->eventTime,
args->pointerCount, args->pointerProperties, args->pointerCoords);
....
MotionEntry* newEntry = new MotionEntry(args->eventTime,
args->deviceId, args->source, policyFlags,
args->action, args->actionButton, args->flags,
args->metaState, args->buttonState,
args->edgeFlags, args->xPrecision, args->yPrecision, args->downTime,
args->displayId,
args->pointerCount, args->pointerProperties, args->pointerCoords, 0, 0);
needWake = enqueueInboundEventLocked(newEntry);
....
if (needWake) {
mLooper->wake();
}
}在该函数中，所做的事情是对于所传递的参数，构造MotionEntry，然后将其加入到enqueueInboundEventLocked之中。然后唤醒其中的looper。
bool InputDispatcher::enqueueInboundEventLocked(EventEntry* entry) {
bool needWake = mInboundQueue.isEmpty();
mInboundQueue.enqueueAtTail(entry);
...
//进行一些事件和窗口相关的判断处理
}Dispatcher开启的线程中，每次循环的操作如何？
bool InputDispatcherThread::threadLoop() {
mDispatcher->dispatchOnce();
return true;
}Dispatcher下dispatchOnce的实现
void InputDispatcher::dispatchOnce() {
...
dispatchOnceInnerLocked(&nextWakeupTime);
...
}void InputDispatcher::dispatchOnceInnerLocked(nsecs_t* nextWakeupTime) {
....
mPendingEvent = mInboundQueue.dequeueAtHead();
....
switch (mPendingEvent->type) {
case EventEntry::TYPE_MOTION: {
MotionEntry* typedEntry = static_cast(mPendingEvent);
if (dropReason == DROP_REASON_NOT_DROPPED && isAppSwitchDue) {
dropReason = DROP_REASON_APP_SWITCH;
}
if (dropReason == DROP_REASON_NOT_DROPPED
&& isStaleEventLocked(currentTime, typedEntry)) {
dropReason = DROP_REASON_STALE;
}
if (dropReason == DROP_REASON_NOT_DROPPED && mNextUnblockedEvent) {
dropReason = DROP_REASON_BLOCKED;
}
done = dispatchMotionLocked(currentTime, typedEntry,
&dropReason, nextWakeupTime);
break;
}
....
}
} 从mInboudQueue中，获取到事件，然后对事件类型进行判断，判断之后调用了dispatchMotionLocked函数，来继续进行事件的传递。
bool InputDispatcher::dispatchMotionLocked(
nsecs_t currentTime, MotionEntry* entry, DropReason* dropReason, nsecs_t* nextWakeupTime) {
....
Vector inputTargets;
if (isPointerEvent) {
// Pointer event. (eg. touchscreen)
//寻找目标窗口
injectionResult = findTouchedWindowTargetsLocked(currentTime,
entry, inputTargets, nextWakeupTime, &conflictingPointerActions);
} else {
// Non touch event. (eg. trackball）
injectionResult = findFocusedWindowTargetsLocked(currentTime,
entry, inputTargets, nextWakeupTime);
}
....
dispatchEventLocked(currentTime, entry, inputTargets);
return true;
} - dispatchEventLocked
void InputDispatcher::dispatchEventLocked(nsecs_t currentTime,
EventEntry* eventEntry, const Vector& inputTargets) {
....
pokeUserActivityLocked(eventEntry);
.....
for (size_t i = 0; i < inputTargets.size(); i++) {
const InputTarget& inputTarget = inputTargets.itemAt(i);
ssize_t connectionIndex = getConnectionIndexLocked(inputTarget.inputChannel);
if (connectionIndex >= 0) {
sp connection = mConnectionsByFd.valueAt(connectionIndex);
prepareDispatchCycleLocked(currentTime, connection, eventEntry, &inputTarget);
}
}
} 获得目标输入，根据InputChannel获取相应的连接，然后调用prepareDispatchCycleLocked()，进行事件的派发。
enqueueDispatchEntriesLocked，在该方法中又调用了startDispatchCycleLocked方法。其实现为
void InputDispatcher::startDispatchCycleLocked(nsecs_t currentTime,
const sp& connection) {
EventEntry* eventEntry = dispatchEntry->eventEntry;
....
switch (eventEntry->type) {
....
case EventEntry::TYPE_MOTION: {
status = connection->inputPublisher.publishMotionEvent( ....);
break;
}
....
}
...
} 至此调用了connection 的inputPublisher的publishMotionEvent方法将事件分发消耗。
InputPublisher定义在InputTransport.cpp中
status_t InputPublisher::publishMotionEvent(...) {
....
InputMessage msg;
msg.header.type = InputMessage::TYPE_MOTION;
msg.body.motion.seq = seq;
msg.body.motion.deviceId = deviceId;
msg.body.motion.source = source;
msg.body.motion.action = action;
msg.body.motion.actionButton = actionButton;
msg.body.motion.flags = flags;
msg.body.motion.edgeFlags = edgeFlags;
msg.body.motion.metaState = metaState;
msg.body.motion.buttonState = buttonState;
msg.body.motion.xOffset = xOffset;
msg.body.motion.yOffset = yOffset;
msg.body.motion.xPrecision = xPrecision;
msg.body.motion.yPrecision = yPrecision;
msg.body.motion.downTime = downTime;
msg.body.motion.eventTime = eventTime;
msg.body.motion.pointerCount = pointerCount;
for (uint32_t i = 0; i < pointerCount; i++) {
msg.body.motion.pointers[i].properties.copyFrom(pointerProperties[i]);
msg.body.motion.pointers[i].coords.copyFrom(pointerCoords[i]);
}
return mChannel->sendMessage(&msg);
}该方法所执行的操作是利用传入的触摸信息，构建点击消息，然后通过InputChannel将消息发送出去。这里引出了InputChannel，在此，我们通InputPublisher的创建反推出InputChannel是何时被引入的，何时被创建的。从而进一步分析其作用。在分析之前先让我们来对上述的分析过程做一个总结。
ReaderThread开启后会从EventHub中轮询获取时间，获取到事件之后，对手将进行一系列的处理，最终将经过一系列处理封装的事件信息通过InputChannel发送出去。
到此，对于输入事件，我们已经分析到了InputChannel，对于其上的具体分析转化，将是接下来分析的核心。
InputChannel
从上面分析可以看到事件传递部分最后是通过InputChannel所发送出去的，那么InputChannel是在何时被创建的呢？何时被InputManager所使用的呢？同时，InputReaderThread和InputDispatcherThread是运行在SystemServer进程中的，而我们的应用进程是和其不在同一个进程中的。这之间一定也是有进程间的通信机制在里面。具体又是如何实现的呢？对于InputChannel这边是事件传递过程中一个比较核心的点。
InputChannel的创建是在 ViewRootImpl中setView方法中。
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
....
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
mInputChannel = new InputChannel();
}
....
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mOutsets, mInputChannel);
....
}这里对于ViewRootImpl和WindowSession相关暂且不介绍，对于这方面的知识，需要很大的篇幅来介绍，这里先只是讲到是在这里创建的，对于其相关的内容将在后续的文章中介绍。这里首先是创建了一个InputChannel，然后将其调用了WindowSession的addToDisplay方法将其作为参数传递。
public InputChannel() {
}在InputChannel中的方法都为调用了相应的native方法。这里调用的addToDisplay将会把InputChannel添加到WindowManagerService中。会调用WMS的addWindow方法。
public int addWindow(Session session, IWindow client, int seq,
WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
Rect outContentInsets, Rect outStableInsets, Rect outOutsets,
InputChannel outInputChannel) {
....
final boolean openInputChannels = (outInputChannel != null
&& (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);
if (openInputChannels) {
win.openInputChannel(outInputChannel);
}
....
}对于InputChannel的相关处理调用了WindowState的openInputChannel方法。
void openInputChannel(InputChannel outInputChannel) {
if (mInputChannel != null) {
throw new IllegalStateException("Window already has an input channel.");
}
String name = makeInputChannelName();
InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
mInputChannel = inputChannels[0];
mClientChannel = inputChannels[1];
mInputWindowHandle.inputChannel = inputChannels[0];
if (outInputChannel != null) {
mClientChannel.transferTo(outInputChannel);
mClientChannel.dispose();
mClientChannel = null;
} else {
mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
}
mService.mInputManager.registerInputChannel(mInputChannel, mInputWindowHandle);
}首先调用了InputChannel的openInputChannelPair方法，该方法调用了InputChannel的native方法nativeOpenInputChannelPair,创建了两个InputChannel，对其中一个通过InputManager进行了InputChannel的注册。对于InputChannel的相关Native的实现是在InputTransport中，nativeOpenInputChannelPair的源码如下。
status_t InputChannel::openInputChannelPair(const String8& name,
sp& outServerChannel, sp& outClientChannel) {
int sockets[2];
if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {
status_t result = -errno;
outServerChannel.clear();
outClientChannel.clear();
return result;
}
int bufferSize = SOCKET_BUFFER_SIZE;
setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
String8 serverChannelName = name;
serverChannelName.append(" (server)");
outServerChannel = new InputChannel(serverChannelName, sockets[0]);
String8 clientChannelName = name;
clientChannelName.append(" (client)");
outClientChannel = new InputChannel(clientChannelName, sockets[1]);
return OK;
} 这里的Socket创建用到了 Linux中的Socketpaire，在之前的版本中是通过管道来实现的，但是 创建的管道只能是单向的 -- mode 只能是 "r" 或 "w" 而不能是某种组合--用户只能选择要么往里写，要么从中读，而不能同时在一个管道中进行读写。实际应用中，经常会有同时进行读写的要求。
Linux实现了一个源自BSD的socketpair调用可以实现上述在同一个文件描述符中进行读写的功能（该调用目前也是POSIX规范的一部分 。该系统调用能创建一对已连接的（UNIX族）无名socket。在Linux中，完全可以把这一对socket当成pipe返回的文件描述符一样使用，唯一的区别就是这一对文件描述符中的任何一个都可读和可写。
socketpair产生的文件描述符是一对socket，socket上的标准操作都可以使用，其中也包括shutdown。——利用shutdown，可以实现一个半关闭操作，通知对端本进程不再发送数据，同时仍可以利用该文件描述符接收来自对端的数据。
status_t InputChannel::sendMessage(const InputMessage* msg) {
size_t msgLength = msg->size();
ssize_t nWrite;
do {
nWrite = ::send(mFd, msg, msgLength, MSG_DONTWAIT | MSG_NOSIGNAL);
} while (nWrite == -1 && errno == EINTR);
.....
return OK;
}接收消息，通过读socket的方式来读取消息。
status_t InputChannel::receiveMessage(InputMessage* msg) {
ssize_t nRead;
do {
nRead = ::recv(mFd, msg, sizeof(InputMessage), MSG_DONTWAIT);
} while (nRead == -1 && errno == EINTR);
......
return OK;
}通过之前的分析，我们已经追踪到了通过InputChannel发送消息的代码，接收端的消息处理是如何呢？是如何触发开始接收消息，消息如何在传到InputChannel之后，进行的进一步的数据传递呢？分析之前，这里先对上面InputChannel进行一个总结。
之前的setView中，我们创建了InputChannel之后，开启了对于InputChannel中输入事件的监听。
if (mInputChannel != null) {
if (mInputQueueCallback != null) {
mInputQueue = new InputQueue();
mInputQueueCallback.onInputQueueCreated(mInputQueue);
}
mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
Looper.myLooper());
}WindowInputEventReceiver的构造函数如下，其继承自InputEventReceiver。
final class WindowInputEventReceiver extends InputEventReceiver {
public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
super(inputChannel, looper);
}
....
}InputEventReceiver的构造函数源码如下
public InputEventReceiver(InputChannel inputChannel, Looper looper) {
....
mInputChannel = inputChannel;
mMessageQueue = looper.getQueue();
mReceiverPtr = nativeInit(new WeakReference(this),
inputChannel, mMessageQueue);
} 这里调用了native方法来做初始化，相关的native方法的实现在android_view_InputEventReceiver.cpp
static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,
jobject inputChannelObj, jobject messageQueueObj) {
....
sp inputChannel = android_view_InputChannel_getInputChannel(env,
inputChannelObj);
sp messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
sp receiver = new NativeInputEventReceiver(env,
receiverWeak, inputChannel, messageQueue);
status_t status = receiver->initialize();
.....
} 根据传入的InputChannel和MessageQueue，创建一个NativeInputEventReceiver，然后调用其initialize方法。
status_t NativeInputEventReceiver::initialize() {
setFdEvents(ALOOPER_EVENT_INPUT);
return OK;
}在initialize()方法中，只调用了一个函数setFdEvents，
void NativeInputEventReceiver::setFdEvents(int events) {
if (mFdEvents != events) {
mFdEvents = events;
int fd = mInputConsumer.getChannel()->getFd();
if (events) {
mMessageQueue->getLooper()->addFd(fd, 0, events, this, NULL);
} else {
mMessageQueue->getLooper()->removeFd(fd);
}
}
}从InputConsumer中获取到channel的fd，然后调用Looper的addFd方法。
int ALooper_addFd(ALooper* looper, int fd, int ident, int events,
ALooper_callbackFunc callback, void* data) {
return ALooper_to_Looper(looper)->addFd(fd, ident, events, callback, data);
}Looper的addFd的实现如下
int Looper::addFd(int fd, int ident, int events, const sp& callback, void* data) {
Request request;
request.fd = fd;
request.ident = ident;
request.events = events;
request.seq = mNextRequestSeq++;
request.callback = callback;
request.data = data;
if (mNextRequestSeq == -1) mNextRequestSeq = 0;
struct epoll_event eventItem;
request.initEventItem(&eventItem);
ssize_t requestIndex = mRequests.indexOfKey(fd);
if (requestIndex < 0) {
int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
if (epollResult < 0) {
return -1;
}
mRequests.add(fd, request);
}
} 该方法所执行的操作就是对传递的fd添加epoll监控，Looper会循环调用pollOnce方法，而pollOnce方法的核心实现就是pollInner。其代码大致实现内容为等待消息的到来，当有消息到来后，根据消息类型做一些判断处理，然后调用其相关的callback。我们当前是对于开启的socket的一个监听，当有数据到来，我们便会执行相应的回调。这里对于InputChannel的回调是在调用了NativeInputEventReceiver的handleEvent方法。
int NativeInputEventReceiver::handleEvent(int receiveFd, int events, void* data) {
.....
if (events & ALOOPER_EVENT_INPUT) {
JNIEnv* env = AndroidRuntime::getJNIEnv();
status_t status = consumeEvents(env, false /*consumeBatches*/, -1, NULL);
mMessageQueue->raiseAndClearException(env, "handleReceiveCallback");
return status == OK || status == NO_MEMORY ? 1 : 0;
}
....
return 1;
}对于Event的处理，这里调用consumeEvents来对事件进行处理。
status_t NativeInputEventReceiver::consumeEvents(JNIEnv* env,
bool consumeBatches, nsecs_t frameTime, bool* outConsumedBatch) {
...
for(;;) {
...
InputEvent* inputEvent;
status_t status = mInputConsumer.consume(&mInputEventFactory,
consumeBatches, frameTime, &seq, &inputEvent);
...
}
...
}InputConsumer是在InputTransport中做的声明。
status_t InputConsumer::consume(InputEventFactoryInterface* factory,
bool consumeBatches, nsecs_t frameTime, uint32_t* outSeq, InputEvent** outEvent) {
while (!*outEvent) {
....
status_t result = mChannel->receiveMessage(&mMsg);
....
}
}调用consume方法会持续的调用InputChannel的receiveMessage方法来从socket中读取数据。到这里，我们已经将写入socket的事件读出来了。InputChannel在创建之后，通过为其InputEventReceiver对其fd进行epoll监控，当有变动的时候，调用InputChannel来接收消息。InputChannel又是如何被设置到InputDispatcher之中的呢？在调用openInputChannel方法，创建Socket的完成之后，调用该方法。
public void registerInputChannel(InputChannel inputChannel,
InputWindowHandle inputWindowHandle) {
if (inputChannel == null) {
throw new IllegalArgumentException("inputChannel must not be null.");
}
nativeRegisterInputChannel(mPtr, inputChannel, inputWindowHandle, false);
}nativeRegisterInputManger
static void nativeRegisterInputChannel(JNIEnv* env, jclass /* clazz */,
jlong ptr, jobject inputChannelObj, jobject inputWindowHandleObj, jboolean monitor) {
NativeInputManager* im = reinterpret_cast(ptr);
sp inputChannel = android_view_InputChannel_getInputChannel(env,
inputChannelObj);
if (inputChannel == NULL) {
throwInputChannelNotInitialized(env);
return;
}
sp inputWindowHandle =
android_server_InputWindowHandle_getHandle(env, inputWindowHandleObj);
status_t status = im->registerInputChannel(
env, inputChannel, inputWindowHandle, monitor);
if (status) {
String8 message;
message.appendFormat("Failed to register input channel. status=%d", status);
jniThrowRuntimeException(env, message.string());
return;
}
if (! monitor) {
android_view_InputChannel_setDisposeCallback(env, inputChannelObj,
handleInputChannelDisposed, im);
}
} NativeInputManager的registerInputChannel还会调用到InputDispatcher的registerInputChannel，会通过InputChannel创建相应的Connection，同时将InputChannel加入到相应的监控之中。在上面对代码的分析之中，获取InputChannel，就是通过这个Connection来获取的。
status_t InputDispatcher::registerInputChannel(const sp& inputChannel,
const sp& inputWindowHandle, bool monitor) {
{ // acquire lock
AutoMutex _l(mLock);
if (getConnectionIndexLocked(inputChannel) >= 0) {
return BAD_VALUE;
}
sp connection = new Connection(inputChannel, inputWindowHandle, monitor);
int fd = inputChannel->getFd();
mConnectionsByFd.add(fd, connection);
if (monitor) {
mMonitoringChannels.push(inputChannel);
}
mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);
} // release lock
// Wake the looper because some connections have changed.
mLooper->wake();
return OK;
} 经过InputManager的层层传递，最终会到达InputDispatcher之中，然后对其进行封装，并在其内部进行保存，同时也传递了相应的窗口的句柄，方便了后期在事件传递的时候，对于窗口的判断。
ViewRootImpl
事件在从socket读出之后，经过传递，最终会调用到ViewRootImpl的enqueueInputEvent方法。
void enqueueInputEvent(InputEvent event,
InputEventReceiver receiver, int flags, boolean processImmediately) {
adjustInputEventForCompatibility(event);
QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
QueuedInputEvent last = mPendingInputEventTail;
if (last == null) {
mPendingInputEventHead = q;
mPendingInputEventTail = q;
} else {
last.mNext = q;
mPendingInputEventTail = q;
}
mPendingInputEventCount += 1;
if (processImmediately) {
doProcessInputEvents();
} else {
scheduleProcessInputEvents();
}
}enqueueInputEvent方法从InputEventReceiver中获取到InputEvent，然后将其加入到当前的事件队列之中，最后调用doProcessInputEvents来进行处理。
void doProcessInputEvents() {
while (mPendingInputEventHead != null) {
QueuedInputEvent q = mPendingInputEventHead;
mPendingInputEventHead = q.mNext;
if (mPendingInputEventHead == null) {
mPendingInputEventTail = null;
}
q.mNext = null;
mPendingInputEventCount -= 1;
long eventTime = q.mEvent.getEventTimeNano();
long oldestEventTime = eventTime;
if (q.mEvent instanceof MotionEvent) {
MotionEvent me = (MotionEvent)q.mEvent;
if (me.getHistorySize() > 0) {
oldestEventTime = me.getHistoricalEventTimeNano(0);
}
}
mChoreographer.mFrameInfo.updateInputEventTime(eventTime, oldestEventTime);
deliverInputEvent(q);
}
if (mProcessInputEventsScheduled) {
mProcessInputEventsScheduled = false;
mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);
}
}遍历所有的消息，如果事件类型为触摸屏事件，对其进行相应的时间修改，最后对于每一个处理完成的事件调用deliverInputEvent,
private void deliverInputEvent(QueuedInputEvent q) {
q.mEvent.getSequenceNumber());
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onInputEvent(q.mEvent, 0);
}
InputStage stage;
if (q.shouldSendToSynthesizer()) {
stage = mSyntheticInputStage;
} else {
stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
}
if (stage != null) {
stage.deliver(q);
} else {
finishInputEvent(q);
}
}在事件分发环节，首先进行事件的一个判断，通过shouldSkipIme来判断是否传递给输入法，然后决定使用何种InputStage进行消息的继续传递，这里实现了多种InputStage，对于每一个类型的InputStage都实现了一个方法process方法来针对不同类型的事件做处理，如果是触摸屏类的消息，最终会将事件的处理转交到View的身上。
InputStage中的事件如何传递处理，传递处理之后，如何进行
对于InputStage涉及的篇幅较多，这里也不再展开，当消息到达ViewRootImpl中后，接下来就是在View间的派发。
参考文章
Linux 上实现双向进程间通信管道