努比亚技术团队原创内容，转载请务必注明出处。
- Native层传递过程
- InputEventReceiver的事件来源于哪里
- InputConsumer
- InputConsumer处理事件
- InputConsumer的构建
- InputChannel
- InputChannel的创建
- server端InputChannel的注册
- client端InputChannel读取事件并传递
- 小结
- InputManagerService
- IMS的创建
- IMS的启动
- 小结
- InputDispatcher
- InputDispatcher启动
- InputDispatcher分发事件
- InputReader（InputDispatcher事件的来源）
- InputReader启动
- InputReader处理事件
- EventHub
- EventHub的创建
- EventHub如何获取输入事件
- EventHub处理reopen设备
- EventHub处理close设备
- EventHub扫描设备
- EventHub处理open设备
- EventHub处理event
- EventHub处理inotify事件
- 小结
Native层传递过程
此小节主要介绍输入事件是如何从InputReader获取，然后InputDispatcher又是如何将它们分发出去，这个过程中使用什么技术进行事件的传递的。
Natvie事件传递时序图
InputEventReceiver的事件来源于哪里
上节中有介绍在Native层NativeInputEventReceiver的consumeEvents方法中会通过jni方式调用Java层的InputEventReceiver的dispatchInputEvent方法将事件传递到上层。那consumeEvents的事件又来源于哪里呢？我们继续看这个consumeEvents方法。
status_t NativeInputEventReceiver::consumeEvents(JNIEnv* env,
bool consumeBatches, nsecs_t frameTime, bool* outConsumedBatch) {
// 省略若干行
for (;;) {
// 省略若干行
InputEvent* inputEvent;
// 这里调用了InputConsumer的consume方法来获取输入事件
status_t status = mInputConsumer.consume(&mInputEventFactory,
consumeBatches, frameTime, &seq, &inputEvent,
&motionEventType, &touchMoveNum, &flag);
// 省略若干行
if (skipCallbacks) {
mInputConsumer.sendFinishedSignal(seq, false);
}
}
}
InputConsumer
consume方法中主要是从InputChannel获取输入事件的信息，然后根据消息中获取的事件类型构造出对应的event，并将消息中的事件信息赋值给event对象。
InputConsumer处理事件
从上面分析我们能够看到，再NativeInputEventReceiver的consumeEvents方法中，会循环调用InputConsumer的consume方法获取事件并进行处理。InputConsumer的consume方法中会通过InputChannel从socket中通过recv系统调用获取下层传递的事件，获取到事件后就会通过jni向Java层传递。
InputConsumer处理事件
status_t InputConsumer::consume(InputEventFactoryInterface* factory, bool consumeBatches,
nsecs_t frameTime, uint32_t* outSeq, InputEvent** outEvent,
int* motionEventType, int* touchMoveNumber, bool* flag) {
// 省略若干行
*outSeq = 0;
*outEvent = nullptr;
// Fetch the next input message.
// Loop until an event can be returned or no additional events are received.
while (!*outEvent) {
if (mMsgDeferred) {
// mMsg contains a valid input message from the previous call to consume
// that has not yet been processed.
mMsgDeferred = false;
} else {
// Receive a fresh message.
// 这里通过调用InputChannel的receiveMessage来获取消息
status_t result = mChannel->receiveMessage(&mMsg);
// 省略若干行
}
// 根据消息的类型生成不同的Event
switch (mMsg.header.type) {
case InputMessage::Type::KEY: {
// 构造一个KeyEvent
KeyEvent* keyEvent = factory->createKeyEvent();
if (!keyEvent) return NO_MEMORY;
// 从msg中获取事件的各属性，并赋值给构造出的Event对象
initializeKeyEvent(keyEvent, &mMsg);
*outSeq = mMsg.body.key.seq;
*outEvent = keyEvent;
if (DEBUG_TRANSPORT_ACTIONS) {
ALOGD("channel '%s' consumer ~ consumed key event, seq=%u",
mChannel->getName().c_str(), *outSeq);
}
break;
}
case InputMessage::Type::MOTION: {
// 构造一个MotionEvent
MotionEvent* motionEvent = factory->createMotionEvent();
if (!motionEvent) return NO_MEMORY;
updateTouchState(mMsg);
// 从msg中获取事件的各属性，并赋值给构造出的Event对象
initializeMotionEvent(motionEvent, &mMsg);
*outSeq = mMsg.body.motion.seq;
*outEvent = motionEvent;
if (DEBUG_TRANSPORT_ACTIONS) {
ALOGD("channel '%s' consumer ~ consumed motion event, seq=%u",
mChannel->getName().c_str(), *outSeq);
}
break;
}
// 省略若干行
}
}
return OK;
}
这里我们先看下event的构造和初始化，输入消息的获取随后再介绍。先看下factory->createMotionEvent，这里factory是PreallocatedInputEventFactory的实例。
class PreallocatedInputEventFactory : public InputEventFactoryInterface {
public:
PreallocatedInputEventFactory() { }
virtual ~PreallocatedInputEventFactory() { }
// 可以看到这里返回的是全局变量的地址
virtual KeyEvent* createKeyEvent() override { return &mKeyEvent; }
virtual MotionEvent* createMotionEvent() override { return &mMotionEvent; }
virtual FocusEvent* createFocusEvent() override { return &mFocusEvent; }
private:
// 这里定义不同类型的事件变量
KeyEvent mKeyEvent;
MotionEvent mMotionEvent;
FocusEvent mFocusEvent;
};
好了，我们继续看event的初始化。这里主要是从msg中获取对应事件的详细信息然后赋值给对应的event对象上。
// 对key事件进行初始化
void InputConsumer::initializeKeyEvent(KeyEvent* event, const InputMessage* msg) {
event->initialize(msg->body.key.eventId, msg->body.key.deviceId, msg->body.key.source,
msg->body.key.displayId, msg->body.key.hmac, msg->body.key.action,
msg->body.key.flags, msg->body.key.keyCode, msg->body.key.scanCode,
msg->body.key.metaState, msg->body.key.repeatCount, msg->body.key.downTime,
msg->body.key.eventTime);
}
// 对motion事件进行初始化
void InputConsumer::initializeMotionEvent(MotionEvent* event, const InputMessage* msg) {
// 省略若干行
event->initialize(msg->body.motion.eventId, msg->body.motion.deviceId, msg->body.motion.source,
msg->body.motion.displayId, msg->body.motion.hmac, msg->body.motion.action,
msg->body.motion.actionButton, msg->body.motion.flags,
msg->body.motion.edgeFlags, msg->body.motion.metaState,
msg->body.motion.buttonState, msg->body.motion.classification,
msg->body.motion.xScale, msg->body.motion.yScale, msg->body.motion.xOffset,
msg->body.motion.yOffset, msg->body.motion.xPrecision,
msg->body.motion.yPrecision, msg->body.motion.xCursorPosition,
msg->body.motion.yCursorPosition, msg->body.motion.downTime,
msg->body.motion.eventTime, pointerCount, pointerProperties, pointerCoords);
}
然后我们继续看msg的获取方法：InputChannel的receiveMessage方法。
status_t InputChannel::receiveMessage(InputMessage* msg) {
ssize_t nRead;
do {
// 这里通过recv系统调用从socket中读取消息
nRead = ::recv(mFd.get(), msg, sizeof(InputMessage), MSG_DONTWAIT);
} while (nRead == -1 && errno == EINTR);
// 省略若干行
return OK;
}
可以看到这个方法主要是从socket中读取消息。那这里的socket是什么时候建立的呢？我们继续向下看。
InputConsumer的构建
在NativeInputEventReceiver的构造方法中，会创建出NativeInputEventReceiver，并将InputChannel传入。而NativeInputEventReceiver的构建是在Java层InputEventReceiver的native方法nativeInit中创建，并且能够看到，这里的InputChannel是从Java层传递下来的。
InputConsumer::InputConsumer(const sp<InputChannel>& channel) :
mResampleTouch(isTouchResamplingEnabled()),
// 初始化InputChannel
mChannel(channel), mMsgDeferred(false) {
}
我们发现在InputConsumer构造时对InputChannel进行了初始化，那就继续超前看InputConsumer在哪里构建的。
NativeInputEventReceiver::NativeInputEventReceiver(JNIEnv* env,
jobject receiverWeak, const sp<InputChannel>& inputChannel,
const sp<MessageQueue>& messageQueue) :
mReceiverWeakGlobal(env->NewGlobalRef(receiverWeak)),
mInputConsumer(inputChannel), mMessageQueue(messageQueue),
mBatchedInputEventPending(false), mFdEvents(0) {
if (kDebugDispatchCycle) {
ALOGD("channel '%s' ~ Initializing input event receiver.", getInputChannelName().c_str());
}
}
回到NativeInputEventReceiver中，发现它的构造方法中传入了InputChannel，那么继续看NativeInputEventReceiver的构建。
static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,
jobject inputChannelObj, jobject messageQueueObj) {
// 通过jni获取java创建的InputChannel
sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
inputChannelObj);
// 省略若干行
// 构建出NativeInputEventReceiver
sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,
receiverWeak, inputChannel, messageQueue);
// 初始化Receiver
status_t status = receiver->initialize();
// 省略若干行
receiver->incStrong(gInputEventReceiverClassInfo.clazz); // retain a reference for the object
return reinterpret_cast<jlong>(receiver.get());
}
通过上述分析，我们发现NativeInputEventReceiver中获取底层事件的InputChannel是来自于Java层的传递，那么，InputChannel又是如何创建的呢？
InputChannel
InputChannel会作为句柄传递到下层，后面分发事件的时候会通过它来进行。而且这里会创建出两个，一个作为server端注册到InputManagerService，最终会注册到InputDispatcher中去，另一个则作为client端来接收server端的事件。
InputChannel的创建
通过前面分析，我们发现NativeInputEventReceiver中的InputChanel来源于Java层的InputChannel。上述nativeInit是Java层InputEventReceiver的native方法，继续看Java层的InputEventReceiver。
InputChannel的创建
public InputEventReceiver(InputChannel inputChannel, Looper looper) {
// 省略若干行
mInputChannel = inputChannel;
mMessageQueue = looper.getQueue();
// 将Java层的inputChannel向下层传递
mReceiverPtr = nativeInit(new WeakReference<InputEventReceiver>(this),
inputChannel, mMessageQueue);
mCloseGuard.open("dispose");
}
Java层InputEventReceiver构造时传入了InputChannel。在ViewRootImpl的setView方法中会创建InputChannel，然后会调用Session的addToDisplayAsUser方法初始化InputChannel
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
int userId) {
synchronized (this) {
if (mView == null) {
// 省略若干行
InputChannel inputChannel = null;
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
inputChannel = new InputChannel();
}
// 省略若干行
// 调用Session的addToDisplayAsUser方法来添加window，
// 会初始化InputChannel
res = mWindowSession.addToDisplayAsUser(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(), userId, mTmpFrame,
mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
mAttachInfo.mDisplayCutout, inputChannel,
mTempInsets, mTempControls);
// 省略若干行
if (inputChannel != null) {
if (mInputQueueCallback != null) {
mInputQueue = new InputQueue();
mInputQueueCallback.onInputQueueCreated(mInputQueue);
}
// 将InputChannel传入InputEventReceiver
mInputEventReceiver = new WindowInputEventReceiver(inputChannel,
Looper.myLooper());
}
// 省略若干行
}
}
}
Session的addToDisplayAsUser方法会继续调用WindowManagerService的addWindow方法。
public int addToDisplayAsUser(IWindow window, int seq, WindowManager.LayoutParams attrs,
int viewVisibility, int displayId, int userId, Rect outFrame,
Rect outContentInsets, Rect outStableInsets,
DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,
InsetsState outInsetsState, InsetsSourceControl[] outActiveControls) {
// 直接调用WindowManagerService的addWindow方法
return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId, outFrame,
outContentInsets, outStableInsets, outDisplayCutout, outInputChannel,
outInsetsState, outActiveControls, userId);
}
addWindow方法中会调用WindowState打开InputChannel。
public int addWindow(Session session, IWindow client, int seq,
LayoutParams attrs, int viewVisibility, int displayId, Rect outFrame,
Rect outContentInsets, Rect outStableInsets,
DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,
InsetsState outInsetsState, InsetsSourceControl[] outActiveControls,
int requestUserId) {
// 省略若干行
final WindowState win = new WindowState(this, session, client, token, parentWindow,
appOp[0], seq, attrs, viewVisibility, session.mUid, userId,
session.mCanAddInternalSystemWindow);
// 省略若干行
final boolean openInputChannels = (outInputChannel != null
&& (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);
if (openInputChannels) {
// 这里会调用WindowState的openInputChannel来打开inputChannel
win.openInputChannel(outInputChannel);
}
// 省略若干行
return res;
}
继续看WindowState的openInputChannel方法。首先会通过调用InputChannel的静态方法openInputChannelPair来创建两个InputChannel，一个作为client一个作为server；然后还会调用InputManagerService的registerInputChannel来注册server端的InputChannel；最后将client端的InputChannel设置到outInputChannel中。
void openInputChannel(InputChannel outInputChannel) {
if (mInputChannel != null) {
throw new IllegalStateException("Window already has an input channel.");
}
String name = getName();
// 通过openInputChannelPair方法创建出两个InputChannel
InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
mInputChannel = inputChannels[0];
mClientChannel = inputChannels[1];
// 注册server端的InputChannel到InputManagerService中
mWmService.mInputManager.registerInputChannel(mInputChannel);
mInputWindowHandle.token = mInputChannel.getToken();
if (outInputChannel != null) {
// 将client端的InputChannel设置到outInputChannel
mClientChannel.transferTo(outInputChannel);
mClientChannel.dispose();
mClientChannel = null;
} else {
// If the window died visible, we setup a dummy input channel, so that taps
// can still detected by input monitor channel, and we can relaunch the app.
// Create dummy event receiver that simply reports all events as handled.
mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
}
mWmService.mInputToWindowMap.put(mInputWindowHandle.token, this);
}
上述openInputChannelPair方法中会直接调用InputChannel的native方法nativeOpenInputChannelPair来创建出一对InputChannel。
public static InputChannel[] openInputChannelPair(String name) {
if (name == null) {
throw new IllegalArgumentException("name must not be null");
}
if (DEBUG) {
Slog.d(TAG, "Opening input channel pair '" + name + "'");
}
// 继续调用natvie方法创建出两个InputChannel
return nativeOpenInputChannelPair(name);
}
jni方法nativeOpenInputChannelPair中会继续调用InputChannel的openInputChannelPair静态方法。然后将创建出的两个inputChannel分别添加到数组中，然后返回给上层。
static jobjectArray android_view_InputChannel_nativeOpenInputChannelPair(JNIEnv* env,
jclass clazz, jstring nameObj) {
ScopedUtfChars nameChars(env, nameObj);
std::string name = nameChars.c_str();
sp<InputChannel> serverChannel;
sp<InputChannel> clientChannel;
// 创建出server端和client端的InputChannel
status_t result = InputChannel::openInputChannelPair(name, serverChannel, clientChannel);
// 省略若干行
// 添加到数组中，然后返回给上层
env->SetObjectArrayElement(channelPair, 0, serverChannelObj);
env->SetObjectArrayElement(channelPair, 1, clientChannelObj);
return channelPair;
}
openInputChannelPair方法中会首先通过socketpair创建一对相互连接的套接字，然后分别给socket设置相应的选项值；然后通过InputChannel的create方法创建出两个分别与socket关联的inuptChannel。
status_t InputChannel::openInputChannelPair(const std::string& name,
sp<InputChannel>& outServerChannel, sp<InputChannel>& outClientChannel) {
int sockets[2];
// 创建一对相互连接的socket
if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {
status_t result = -errno;
// 创建失败做相应的处理
ALOGE("channel '%s' ~ Could not create socket pair. errno=%d",
name.c_str(), errno);
outServerChannel.clear();
outClientChannel.clear();
return result;
}
// 分别设置两个socket的可读可写buffer
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));
sp<IBinder> token = new BBinder();
std::string serverChannelName = name + " (server)";
android::base::unique_fd serverFd(sockets[0]);
// 创建出server端InputChannel，并于socket关联
outServerChannel = InputChannel::create(serverChannelName, std::move(serverFd), token);
std::string clientChannelName = name + " (client)";
android::base::unique_fd clientFd(sockets[1]);
// 创建出client端InputChannel，并于socket关联
outClientChannel = InputChannel::create(clientChannelName, std::move(clientFd), token);
return OK;
}
通过InputChannel的create方法构建出InputChannel并返回。
sp<InputChannel> InputChannel::create(const std::string& name, android::base::unique_fd fd,
sp<IBinder> token) {
// 设置文件描述符fd的状态属性为O_NONBLOCK
const int result = fcntl(fd, F_SETFL, O_NONBLOCK);
if (result != 0) {
LOG_ALWAYS_FATAL("channel '%s' ~ Could not make socket non-blocking: %s", name.c_str(),
strerror(errno));
return nullptr;
}
// 创建出InputChannel并返回
return new InputChannel(name, std::move(fd), token);
}
至此，InputChannel便创建并关联上socket上了。并且通过前面的介绍，我们知道了获取输入事件时是从client端的socket中读取消息并进行事件封装，然后传递到上层。但是这里我们发现有一个问题，就是client端socket中的数据是从哪里来的呢？我们继续看一下WindowState的openInputChannel方法。
server端InputChannel的注册
在通过openInputChannel开启InputChannel后，会调用了InputManagerService的registerInputChannel方法注册server端的InputChannel
server端InputChannel的注册
void openInputChannel(InputChannel outInputChannel) {
// 省略若干行
// 通过openInputChannelPair方法创建出两个InputChannel
InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
mInputChannel = inputChannels[0];
mClientChannel = inputChannels[1];
// 注册server端的InputChannel到InputManagerService中
mWmService.mInputManager.registerInputChannel(mInputChannel);
// 省略若干行
}
我们发现server端的InputChannel被注册到了InputManagerService中去了，那么，我们继续向下看。
public void registerInputChannel(InputChannel inputChannel) {
if (inputChannel == null) {
throw new IllegalArgumentException("inputChannel must not be null.");
}
// 调用native方法继续注册
nativeRegisterInputChannel(mPtr, inputChannel);
}
在InputManagerService的registerInputChannel方法中直接调用了native方法nativeRegisterInputChannel，我们继续。
static void nativeRegisterInputChannel(JNIEnv* env, jclass /* clazz */,
jlong ptr, jobject inputChannelObj) {
NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);
// 获取InputChannel
sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
inputChannelObj);
if (inputChannel == nullptr) {
throwInputChannelNotInitialized(env);
return;
}
// 将inputChannel注册到NativeInputManager中
status_t status = im->registerInputChannel(env, inputChannel);
// 设置dispose的callback，在inputChannel
// dispose之后会调用函数指针handleInputChannelDisposed
// 来调用NativeInputManager的unregisterInputChannel
// 解注册inputChannel
android_view_InputChannel_setDisposeCallback(env, inputChannelObj,
handleInputChannelDisposed, im);
}
在native方法中，先调用了NativeInputManager的registerInputChannel方法注册inputChannel，然后会给inputChannel设置dispose callback，并且callback中执行了inputChannel的解注册。在NativeInputManager的registerInputChannel方法中，会获取InputDispatcher，并将inputChannel注册到其中去。
status_t NativeInputManager::registerInputChannel(JNIEnv* /* env */,
const sp<InputChannel>& inputChannel) {
ATRACE_CALL();
return mInputManager->getDispatcher()->registerInputChannel(inputChannel);
}
在InputDispatcher的registerInputChannel方法中，会通过InputChannel构建出Connection，然后将其添加到注册列表当中。
status_t InputDispatcher::registerInputChannel(const sp<InputChannel>& inputChannel) {
#if DEBUG_REGISTRATION
ALOGD("channel '%s' ~ registerInputChannel", inputChannel->getName().c_str());
#endif
{ // acquire lock
std::scoped_lock _l(mLock);
// 省略若干行
// 创建connection并添加的注册列表中
sp<Connection> connection = new Connection(inputChannel, false /*monitor*/, mIdGenerator);
int fd = inputChannel->getFd();
mConnectionsByFd[fd] = connection;
mInputChannelsByToken[inputChannel->getConnectionToken()] = inputChannel;
// 将inputChannel的fd添加到looper中，并且对应的event是ALOOPER_EVENT_INPUT
// 传入的looper callback为handleReceiveCallback方法，
// 因此当事件到来时，会触发此callback
mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);
} // release lock
// Wake the looper because some connections have changed.
mLooper->wake();
return OK;
}
好了，到这里我们就知道了，server端的inputChannel最终被注册到了InputDispatcher的注册列表中去了，所以InputDispatcher中就可以通过向server端的socket中写入消息，然后client端就可以读取到了。但是，这里还发现存在一个问题：那就是server端写入事件消息后，怎么通知到client去开始处理呢？我们在回过头来看一下前面介绍的InputEventReceiver的构造函数。
client端InputChannel读取事件并传递
public InputEventReceiver(InputChannel inputChannel, Looper looper) {
// 省略若干层
mInputChannel = inputChannel;
mMessageQueue = looper.getQueue();
// 将Java层的inputChannel向下层传递
mReceiverPtr = nativeInit(new WeakReference<InputEventReceiver>(this),
inputChannel, mMessageQueue);
mCloseGuard.open("dispose");
}
在InputEventReceiver的构造方法中调用了native方法nativeInit进行native层的初始化
static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,
jobject inputChannelObj, jobject messageQueueObj) {
// 省略若干行
sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,
receiverWeak, inputChannel, messageQueue);
// 初始化Receiver
status_t status = receiver->initialize();
// 省略若干行
return reinterpret_cast<jlong>(receiver.get());
}
在NativeInputEventReceiver初始化时，会将inputChannel的文件描述符fd添加到looper中去，并且添加了looper callback为NativeInputEventReceiver实例自身，所以，当server端写入事件消息时，就会触发callback，于是便调用到NativeInputEventReceiver的handleEvent方法。
status_t NativeInputEventReceiver::initialize() {
// 设置文件描述符对应的event为ALOOPER_EVENT_INPUT
setFdEvents(ALOOPER_EVENT_INPUT);
return OK;
}
void NativeInputEventReceiver::setFdEvents(int events) {
if (mFdEvents != events) {
mFdEvents = events;
int fd = mInputConsumer.getChannel()->getFd();
if (events) {
// 将inputChannel的文件描述符添加到looper中
// 对应的event为ALOOPER_EVENT_INPUT
// 并传入了this作为loopercallback
mMessageQueue->getLooper()->addFd(fd, 0, events, this, nullptr);
} else {
mMessageQueue->getLooper()->removeFd(fd);
}
}
}
我们发现在handleEvent方法中，调用了consumeEvents方法来处理事件，而consumeEvents方法便是我们前面介绍过了的，在其内部会通过jni的方式将事件向Java层传递到InputEventReceiver的dispatchInputEvent，从而便实现了事件的分发。
int NativeInputEventReceiver::handleEvent(int receiveFd, int events, void* data) {
// 省略若干行
// 接收添加的ALOOPER_EVENT_INPUT事件
if (events & ALOOPER_EVENT_INPUT) {
JNIEnv* env = AndroidRuntime::getJNIEnv();
// 调用consumeEvents方法处理事件
status_t status = consumeEvents(env, false /*consumeBatches*/, -1, nullptr);
mMessageQueue->raiseAndClearException(env, "handleReceiveCallback");
return status == OK || status == NO_MEMORY ? 1 : 0;
}
// 省略若干行
return 1;
}
小结
通过以上分析，我们便明白了InputDispatcher是如果通过InputChannel将事件向上层进行分发的整个过程。首先是创建一对InputChannel，并且会开启一对相互连接的socket作为事件传递的媒介。server端的InputChannel会注册到InputDispatcher中去以完成事件的分发，并且会将其fd添加到looper中，而client端的InputChannel会在InputEventReceiver初始化时也会将其fd添加到looper中，并传入callback类接收server端写入的事件，这样整个过程便串联起来了。但是，这里还存在一个问题：InputDispatcher的事件从哪里来呢？
InputManagerService
InputManagerService简称IMS，和其他系统服务一样，是在SystemServer中创建并启动，它主要是用来监测和加工输入事件，并向上层传递。而且，上文所说的InputDispatcher以及InputReader均是在InputManagerService中构建出来的。
IMS的创建
在SystemServer的startOtherServices方法中，直接通过new的方式创建出IMS实例。
private void startOtherServices(@NonNull TimingsTraceAndSlog t) {
// 省略若干行
t.traceBegin("StartInputManagerService");
// 创建IMS
inputManager = new InputManagerService(context);
t.traceEnd();
// 省略若干行
}
InputManagerService的构造方法中，会先创建出Handler，然后通过native方法nativeInit来实现IMS的初始化，主要是构建native层的IMS。
public InputManagerService(Context context) {
this.mContext = context;
// 创建出handler
this.mHandler = new InputManagerHandler(DisplayThread.get().getLooper());
// 省略若干行
// 调用native方法来构建native层IMS
mPtr = nativeInit(this, mContext, mHandler.getLooper().getQueue());
// 省略若干行
}
native方法中先获取到上层传下来的messageQueue，然后获取对应的Looper，并构建出NativeInputManager。
static jlong nativeInit(JNIEnv* env, jclass /* clazz */,
jobject serviceObj, jobject contextObj, jobject messageQueueObj) {
// 获取上层传递的MessageQueue
sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
if (messageQueue == nullptr) {
jniThrowRuntimeException(env, "MessageQueue is not initialized.");
return 0;
}
// 构建NativeInputManager
NativeInputManager* im = new NativeInputManager(contextObj, serviceObj,
messageQueue->getLooper());
im->incStrong(0);
return reinterpret_cast<jlong>(im);
}
NativeInputManager构造中，先创建出native层IMS实例，然后将其添加到serviceManager中。
NativeInputManager::NativeInputManager(jobject contextObj,
jobject serviceObj, const sp<Looper>& looper) :
mLooper(looper), mInteractive(true) {
// 省略若干行
// 构建出native层的IMS，即InputManager
mInputManager = new InputManager(this, this);
// 将IMS添加到serviceManager中
defaultServiceManager()->addService(String16("inputflinger"),
mInputManager, false);
}
在InputManager构建时，会分别创建出InputDispatcher、InputListener以及InputReader实例。这里将InputDispatcher作为InputListener传递到InputClassifier，并最终传递到InputReader中去。
InputManager::InputManager(
const sp<InputReaderPolicyInterface>& readerPolicy,
const sp<InputDispatcherPolicyInterface>& dispatcherPolicy) {
mDispatcher = createInputDispatcher(dispatcherPolicy);
mClassifier = new InputClassifier(mDispatcher);
mReader = createInputReader(readerPolicy, mClassifier);
}
通过以上分析，我们发现在IMS创建的最后，会创建出InputDispatcher和InputReader，InputDispatcher我们前面已经介绍了，主要是用于分发事件；而InputReader是用来获取底层输入事件的，这个我们后面会介绍到。
IMS的启动
我们继续来看SystemServer的startCoreServices方法，在创建出IMS实例后，会调用其的start方法来启动服务。
private void startOtherServices(@NonNull TimingsTraceAndSlog t) {
// 省略若干行
t.traceBegin("StartInputManager");
// 将WindowCallback传递给IMS
inputManager.setWindowManagerCallbacks(wm.getInputManagerCallback());
// 调用start启动服务
inputManager.start();
t.traceEnd();
// 省略若干行
}
start方法中会直接调用native的nativeStart方法来启动native层的IMS。
public void start() {
Slog.i(TAG, "Starting input manager");
// 调用native方法来启动底层IMS
nativeStart(mPtr);
// 省略若干行
}
nativeStart方法中会获取到InputManager，然后调用它的start方法。
static void nativeStart(JNIEnv* env, jclass /* clazz */, jlong ptr) {
NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);
// 调用InputManager的start方法
status_t result = im->getInputManager()->start();
if (result) {
jniThrowRuntimeException(env, "Input manager could not be started.");
}
}
在InputManager的start方法中，先调用了InputDispatcher的start方法来启动InputDispatcher，然后调用InputReader的start方法启动InputReader。
status_t InputManager::start() {
status_t result = mDispatcher->start();
if (result) {
ALOGE("Could not start InputDispatcher thread due to error %d.", result);
return result;
}
result = mReader->start();
if (result) {
ALOGE("Could not start InputReader due to error %d.", result);
mDispatcher->stop();
return result;
}
return OK;
}
小结
通过以上IMS的创建和启动过程分析，我们能够看到在IMS的创建和启动都是在SystemServer的startCoreServices方法中触发的，另外在创建的时候也会分别创建出InputDispatcher和InputReader；而且，在调用start方法启动的时候，最终也会触发调用InputDispatcher和InputReader的start方法来启动各自实例。
InputDispatcher
通过上述分析，知道了InputDispatcher的创建是在IMS创建时创建，那么它是如何启动起来的呢？我们继续看InputDispatcher的start方法。
InputDispatcher启动
在InputDispatcher的start方法中，会创建出InputThread线程，并传入了两个函数指针：dispatchOnce以及mLooper->wake。
status_t InputDispatcher::start() {
if (mThread) {
return ALREADY_EXISTS;
}
// 直接构造出Thread，传入两个回调函数
mThread = std::make_unique<InputThread>(
"InputDispatcher", [this]() { dispatchOnce(); }, [this]() { mLooper->wake(); });
return OK;
}
继续看InputThread的构造过程，发现初始化列表中对传入的回调函数进行了保存，然后构建InputThreadImpl并调用其run方法将线程启动起来。
InputThread::InputThread(std::string name, std::function<void()> loop, std::function<void()> wake)
// 这里保存wake回调函数
: mName(name), mThreadWake(wake) {
// 将loop函数传入InputThreadImpl
mThread = new InputThreadImpl(loop);
mThread->run(mName.c_str(), ANDROID_PRIORITY_URGENT_DISPLAY);
}
InputThread::~InputThread() {
mThread->requestExit();
// 调用wake函数
if (mThreadWake) {
mThreadWake();
}
mThread->requestExitAndWait();
}
class InputThreadImpl : public Thread {
public:
explicit InputThreadImpl(std::function<void()> loop)
// 保存loop函数
: Thread(/* canCallJava */ true), mThreadLoop(loop) {}
~InputThreadImpl() {}
private:
std::function<void()> mThreadLoop;
bool threadLoop() override {
// 在线程的loop循环中调用了传入的loop函数。
mThreadLoop();
// 返回true线程会一直运行，直到requestExit被调用时退出
return true;
}
};
通过以上分析，我们发现InputThread构造时会创建出线程并将其启动起来，传入的loop函数（dispatchOnce）最终会作为线程的loop来执行，而wake函数（mLooper->wake）也会在InputThread析构时调用。
InputDispatcher分发事件
通过前面的介绍，我们了解到在InputDispatcher启动时创建了线程，并且将dispatchOnce作为线程的执行函数传入到InputThread中。所以，当InputDispatcher线程被唤醒后就会执行dispatchOnce方法来分发事件。
InputDispatcher分发事件
我们继续，在dispatchOnce方法中，首先会判断是否有command需要处理（如：configChanged，focusChanged等），如果有就会调用runCommandsLockedInterruptible方法执行所有command，然后会再次触发wake执行事件的处理；如果没有则直接调用dispatchOnceInnerLocked来处理输入事件；最后，looper会再次进入睡眠等待下一次唤醒。
void InputDispatcher::dispatchOnce() {
nsecs_t nextWakeupTime = LONG_LONG_MAX;
{ // acquire lock
std::scoped_lock _l(mLock);
mDispatcherIsAlive.notify_all();
// Run a dispatch loop if there are no pending commands.
// The dispatch loop might enqueue commands to run afterwards.
if (!haveCommandsLocked()) {
// 这里没有command需要处理，就开始分发事件
dispatchOnceInnerLocked(&nextWakeupTime);
}
// Run all pending commands if there are any.
// If any commands were run then force the next poll to wake up immediately.
// 处理command，并修改nextWakeupTime
if (runCommandsLockedInterruptible()) {
nextWakeupTime = LONG_LONG_MIN;
}
// If we are still waiting for ack on some events,
// we might have to wake up earlier to check if an app is anr'ing.
// 检测是否事件分发出现anr
const nsecs_t nextAnrCheck = processAnrsLocked();
nextWakeupTime = std::min(nextWakeupTime, nextAnrCheck);
// We are about to enter an infinitely long sleep, because we have no commands or
// pending or queued events
if (nextWakeupTime == LONG_LONG_MAX) {
mDispatcherEnteredIdle.notify_all();
}
} // release lock
// Wait for callback or timeout or wake. (make sure we round up, not down)
nsecs_t currentTime = now();
int timeoutMillis = toMillisecondTimeoutDelay(currentTime, nextWakeupTime);
// 处理完成后调用looper的pollOnce进入睡眠状态，等待下一次唤醒，
// 如果是处理了command，则这个timeoutMillis为0
// 所以会接着执行一次loop
mLooper->pollOnce(timeoutMillis);
}
dispatchOnceInnerLocked方法会先判断是否有待分发的事件，没有则从事件队列中取出一个事件；然后根据事件不同的type调用不同的dispatch方法进行事件分发。
void InputDispatcher::dispatchOnceInnerLocked(nsecs_t* nextWakeupTime) {
// 省略若干行
// Ready to start a new event.
// If we don't already have a pending event, go grab one.
if (!mPendingEvent) {
// 如果没有待分发的事件
if (mInboundQueue.empty()) {
// 省略若干行
// Nothing to do if there is no pending event.
// 事件队列为空，并且没有待分发的事件，直接返回
if (!mPendingEvent) {
return;
}
} else {
// Inbound queue has at least one entry.
// 从队列中取出一个事件
mPendingEvent = mInboundQueue.front();
mInboundQueue.pop_front();
traceInboundQueueLengthLocked();
}
// 省略若干行
switch (mPendingEvent->type) {
// 省略若干行
// 根据事件的type分别进行处理
case EventEntry::Type::KEY: {
KeyEntry* typedEntry = static_cast<KeyEntry*>(mPendingEvent);
// 省略若干行
// 分发key事件
done = dispatchKeyLocked(currentTime, typedEntry, &dropReason, nextWakeupTime);
break;
}
case EventEntry::Type::MOTION: {
// 省略若干行
// 分发motion事件
done = dispatchMotionLocked(currentTime, typedEntry, &dropReason, nextWakeupTime);
break;
}
}
}
这里以key事件为例继续介绍，dispatchKeyLocked中首先通过findFocusedWindowTargetsLocked方法查找到焦点窗口，然后调用dispatchEventLocked朝焦点窗口上分发事件。
bool InputDispatcher::dispatchKeyLocked(nsecs_t currentTime, KeyEntry* entry,
DropReason* dropReason, nsecs_t* nextWakeupTime) {
// 省略若干行
// Identify targets.
std::vector<InputTarget> inputTargets;
// 查找focus window
int32_t injectionResult =
findFocusedWindowTargetsLocked(currentTime, *entry, inputTargets, nextWakeupTime);
// 省略若干行
// 将事件分发到对应window上去
dispatchEventLocked(currentTime, entry, inputTargets);
return true;
}
dispatchEventLocked方法中会遍历所有查找到的focus窗口（inputTarget），然后通过inputChannel获取到链接对象connection，最后通过prepareDispatchCycleLocked将事件分发出去。
void InputDispatcher::dispatchEventLocked(nsecs_t currentTime, EventEntry* eventEntry,
const std::vector<InputTarget>& inputTargets) {
// 省略若干行
// 遍历所有的inputTarget
for (const InputTarget& inputTarget : inputTargets) {
// 通过inputChannel获取connection
sp<Connection> connection =
getConnectionLocked(inputTarget.inputChannel->getConnectionToken());
if (connection != nullptr) {
// 开始事件分发
prepareDispatchCycleLocked(currentTime, connection, eventEntry, inputTarget);
}
// 省略若干行
}
}
prepareDispatchCycleLocked方法中先判断是否需要split motion事件并进行处理，最后调用enqueueDispatchEntriesLocked方法将待分发的事件添加到mOutboundQueue队列中。
void InputDispatcher::prepareDispatchCycleLocked(nsecs_t currentTime,
const sp<Connection>& connection,
EventEntry* eventEntry,
const InputTarget& inputTarget) {
// 省略若干行
// Split a motion event if needed.
// 如果需要split motion事件则进行处理
if (inputTarget.flags & InputTarget::FLAG_SPLIT) {
LOG_ALWAYS_FATAL_IF(eventEntry->type != EventEntry::Type::MOTION,
"Entry type %s should not have FLAG_SPLIT",
EventEntry::typeToString(eventEntry->type));
const MotionEntry& originalMotionEntry = static_cast<const MotionEntry&>(*eventEntry);
if (inputTarget.pointerIds.count() != originalMotionEntry.pointerCount) {
// 省略若干行
enqueueDispatchEntriesLocked(currentTime, connection, splitMotionEntry, inputTarget);
splitMotionEntry->release();
return;
}
}
// Not splitting. Enqueue dispatch entries for the event as is.
// 将将要分发的事件入队
enqueueDispatchEntriesLocked(currentTime, connection, eventEntry, inputTarget);
}
enqueueDispatchEntriesLocked方法中会分别处理不同的flag对应的事件将其添加到outboundQueue中，最后通过调用startDispatchCycleLocked开始事件的分发。
void InputDispatcher::enqueueDispatchEntriesLocked(nsecs_t currentTime,
const sp<Connection>& connection,
EventEntry* eventEntry,
const InputTarget& inputTarget) {
// 省略若干行
bool wasEmpty = connection->outboundQueue.empty();
// 分别处理不同flag对应的event，并将其添加到outboundQueue队列中
// Enqueue dispatch entries for the requested modes.
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_HOVER_EXIT);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_OUTSIDE);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_HOVER_ENTER);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_IS);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_SLIPPERY_EXIT);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_SLIPPERY_ENTER);
// If the outbound queue was previously empty, start the dispatch cycle going.
if (wasEmpty && !connection->outboundQueue.empty()) {
// 如果有event被添加到队列则开始处理
startDispatchCycleLocked(currentTime, connection);
}
}
startDispatchCycleLocked方法中通过遍历outboundQueue队列，取出所有的event，然后根据其type分别调用InputPublisher的publishXxxEvent将事件分发出去。
void InputDispatcher::startDispatchCycleLocked(nsecs_t currentTime,
const sp<Connection>& connection) {
// 省略若干行
// 循环遍历outboundQueue队列
while (connection->status == Connection::STATUS_NORMAL && !connection->outboundQueue.empty()) {
// 从outboundQueue队列取出事件
DispatchEntry* dispatchEntry = connection->outboundQueue.front();
dispatchEntry->deliveryTime = currentTime;
const nsecs_t timeout =
getDispatchingTimeoutLocked(connection->inputChannel->getConnectionToken());
dispatchEntry->timeoutTime = currentTime + timeout;
// Publish the event.
status_t status;
EventEntry* eventEntry = dispatchEntry->eventEntry;
// 根据event的不同type分别进行分发
switch (eventEntry->type) {
case EventEntry::Type::KEY: {
const KeyEntry* keyEntry = static_cast<KeyEntry*>(eventEntry);
std::array<uint8_t, 32> hmac = getSignature(*keyEntry, *dispatchEntry);
// Publish the key event.
// 分发key事件
status =
connection->inputPublisher
.publishKeyEvent(dispatchEntry->seq, dispatchEntry->resolvedEventId,
keyEntry->deviceId, keyEntry->source,
keyEntry->displayId, std::move(hmac),
dispatchEntry->resolvedAction,
dispatchEntry->resolvedFlags, keyEntry->keyCode,
keyEntry->scanCode, keyEntry->metaState,
keyEntry->repeatCount, keyEntry->downTime,
keyEntry->eventTime);
break;
}
case EventEntry::Type::MOTION: {
MotionEntry* motionEntry = static_cast<MotionEntry*>(eventEntry);
PointerCoords scaledCoords[MAX_POINTERS];
const PointerCoords* usingCoords = motionEntry->pointerCoords;
// 省略若干行
// 分发motion事件
// Publish the motion event.
status = connection->inputPublisher
.publishMotionEvent(dispatchEntry->seq,
dispatchEntry->resolvedEventId,
motionEntry->deviceId, motionEntry->source,
motionEntry->displayId, std::move(hmac),
dispatchEntry->resolvedAction,
motionEntry->actionButton,
dispatchEntry->resolvedFlags,
motionEntry->edgeFlags, motionEntry->metaState,
motionEntry->buttonState,
motionEntry->classification, xScale, yScale,
xOffset, yOffset, motionEntry->xPrecision,
motionEntry->yPrecision,
motionEntry->xCursorPosition,
motionEntry->yCursorPosition,
motionEntry->downTime, motionEntry->eventTime,
motionEntry->pointerCount,
motionEntry->pointerProperties, usingCoords);
reportTouchEventForStatistics(*motionEntry);
break;
}
// 省略若干行
}
}
这里以key事件为例继续介绍，在publishKeyEvent方法中，首先会根据传入的event详细信息构建出InputMessage，然后再调用InputChannel的sendMessage方法将msg发送出去。
status_t InputPublisher::publishKeyEvent(uint32_t seq, int32_t eventId, int32_t deviceId,
int32_t source, int32_t displayId,
std::array<uint8_t, 32> hmac, int32_t action,
int32_t flags, int32_t keyCode, int32_t scanCode,
int32_t metaState, int32_t repeatCount, nsecs_t downTime,
nsecs_t eventTime) {
// 省略若干行
// 根据event信息构建InputMessage
InputMessage msg;
msg.header.type = InputMessage::Type::KEY;
msg.body.key.seq = seq;
msg.body.key.eventId = eventId;
msg.body.key.deviceId = deviceId;
msg.body.key.source = source;
msg.body.key.displayId = displayId;
msg.body.key.hmac = std::move(hmac);
msg.body.key.action = action;
msg.body.key.flags = flags;
msg.body.key.keyCode = keyCode;
msg.body.key.scanCode = scanCode;
msg.body.key.metaState = metaState;
msg.body.key.repeatCount = repeatCount;
msg.body.key.downTime = downTime;
msg.body.key.eventTime = eventTime;
// 通过InputChannel的sendMessage方法将event发送出去
return mChannel->sendMessage(&msg);
}
sendMessage主要就是先copy一份事件msg，然后调用send将msg循环写入socket，从而实现输入事件的分发。
status_t InputChannel::sendMessage(const InputMessage* msg) {
const size_t msgLength = msg->size();
InputMessage cleanMsg;
// copy一份msg
msg->getSanitizedCopy(&cleanMsg);
ssize_t nWrite;
do {
// 通过socket循环写入msg
nWrite = ::send(mFd.get(), &cleanMsg, msgLength, MSG_DONTWAIT | MSG_NOSIGNAL);
} while (nWrite == -1 && errno == EINTR);
// 省略若干行
return OK;
}
InputReader（InputDispatcher事件的来源）
InputDispatcher中的事件是从InputReader中来的，InputReader从EventHub中获取到输入事件后，会通过调用InputDispatcher的notifyXxx方法来将事件传递到InuptDispatcher中。
InputReader启动
在IMS的start方法中会调用InputReader的start方法来启动InputReader，我们继续看InputReader的start方法。在start方法中，会创建出InputThread线程，这里注意，创建线程时传入了两个函数指针（laumda表达式）：loopOnce和mEventHub->wake。通过上面对InputThread的介绍，我们知道最终，loopOnce会作为线程的循环方法进行调用，而mEventHub->wake最终也会在线程析构时触发。
status_t InputReader::start() {
if (mThread) {
return ALREADY_EXISTS;
}
// 直接构造出Thread，传入两个回调函数
mThread = std::make_unique<InputThread>(
"InputReader", [this]() { loopOnce(); }, [this]() { mEventHub->wake(); });
return OK;
}
InputReader处理事件
InputReader在其线程的threadLoop中会调用loopOnce从EventHub中获取输入事件，如果获取到事件，则继续调用processEventsLocked进行处理。接着会调用到InputDevice -> InputMapper -> InputDispatcher(InputListenerInterface)，在InputDispatcher中触发notifyXxx方法，从而将事件分发出去。
InputReader处理事件
void InputReader::loopOnce() {
int32_t oldGeneration;
int32_t timeoutMillis;
bool inputDevicesChanged = false;
std::vector<InputDeviceInfo> inputDevices;
// 省略若干行
// 从EventHub中获取事件
size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE);
{ // acquire lock
AutoMutex _l(mLock);
mReaderIsAliveCondition.broadcast();
// 获取到输入事件则调用processEventsLocked进行处理
if (count) {
processEventsLocked(mEventBuffer, count);
}
// 省略若干行
}
processEventsLocked方法中会根据事件的type，分别处理device的变更事件以及输入事件。输入事件则继续调用processEventsForDeviceLocked来处理，device改变则同步改变mDevices。
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) {
// 省略若干行
// 这里事件类型如果不是device change事件则继续处理
processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
} else {
// device change事件
switch (rawEvent->type) {
case EventHubInterface::DEVICE_ADDED:
// device接入，将device添加到全局map中（mDevices）
addDeviceLocked(rawEvent->when, rawEvent->deviceId);
break;
case EventHubInterface::DEVICE_REMOVED: // device断开
removeDeviceLocked(rawEvent->when, rawEvent->deviceId);
break;
case EventHubInterface::FINISHED_DEVICE_SCAN: // device scan
handleConfigurationChangedLocked(rawEvent->when);
break;
default:
ALOG_ASSERT(false); // can't happen
break;
}
}
count -= batchSize;
rawEvent += batchSize;
}
}
processEventsForDeviceLocked中从device的map中根据eventHubId查找device，如果找到则调用对应device的process方法继续处理。
void InputReader::processEventsForDeviceLocked(int32_t eventHubId, const RawEvent* rawEvents,
size_t count) {
// 通过eventHubId从map中查找InputDevice
auto deviceIt = mDevices.find(eventHubId);
if (deviceIt == mDevices.end()) {
// 没有对应的device则直接返回
ALOGW("Discarding event for unknown eventHubId %d.", eventHubId);
return;
}
std::shared_ptr<InputDevice>& device = deviceIt->second;
// device被忽略则返回
if (device->isIgnored()) {
// ALOGD("Discarding event for ignored deviceId %d.", deviceId);
return;
}
// 调用InputDevice的process继续处理事件
device->process(rawEvents, count);
}
InputDevice的process中会遍历所有的event，并且根据event中的deviceId从mDevices中找到对应的device，然后遍历其所有的InputMapper，并调用mapper的process进行事件处理。
void InputDevice::process(const RawEvent* rawEvents, size_t count) {
// Process all of the events in order for each mapper.
// We cannot simply ask each mapper to process them in bulk because mappers may
// have side-effects that must be interleaved. For example, joystick movement events and
// gamepad button presses are handled by different mappers but they should be dispatched
// in the order received.
for (const RawEvent* rawEvent = rawEvents; count != 0; rawEvent++) {
// 省略若干行
// 从devices中找到对应的device，然后遍历其所有inputMapper，并调用其process方法进行处理
for_each_mapper_in_subdevice(rawEvent->deviceId, [rawEvent](InputMapper& mapper) {
mapper.process(rawEvent);
});
--count;
}
}
inline void for_each_mapper_in_subdevice(int32_t eventHubDevice,
std::function<void(InputMapper&)> f) {
auto deviceIt = mDevices.find(eventHubDevice);
// 查找对应的device
if (deviceIt != mDevices.end()) {
auto& devicePair = deviceIt->second;
auto& mappers = devicePair.second;
// 遍历该device的所有InputMapper，并调用函数指针f
for (auto& mapperPtr : mappers) {
f(*mapperPtr);
}
}
}
InputMapper在InputReader中处理device接入事件触发时会调用addDeviceLocked方法，然后会调用到createDeviceLocked方法来创建出对应的InputDevice，创建出device后，便调用它的addEventHubDevice来创建出相应的InputMapper并添加到全局map中。
void InputReader::addDeviceLocked(nsecs_t when, int32_t eventHubId) {
// 根据eventHubId查找device
if (mDevices.find(eventHubId) != mDevices.end()) {
ALOGW("Ignoring spurious device added event for eventHubId %d.", eventHubId);
return;
}
InputDeviceIdentifier identifier = mEventHub->getDeviceIdentifier(eventHubId);
// 创建device
std::shared_ptr<InputDevice> device = createDeviceLocked(eventHubId, identifier);
// 省略若干行
}
std::shared_ptr<InputDevice> InputReader::createDeviceLocked(
int32_t eventHubId, const InputDeviceIdentifier& identifier) {
// 省略若干行
std::shared_ptr<InputDevice> device;
if (deviceIt != mDevices.end()) {
// 如果device已经存在则直接返回
device = deviceIt->second;
} else {
// 否则创建出对应的InputDevice
int32_t deviceId = (eventHubId < END_RESERVED_ID) ? eventHubId : nextInputDeviceIdLocked();
device = std::make_shared<InputDevice>(&mContext, deviceId, bumpGenerationLocked(),
identifier);
}
// 调用addEventHubDevice，构建出相应的mapper
device->addEventHubDevice(eventHubId);
return device;
}
通过addEventHubDevice方法，可以看出针对不同的device类型，会构建出不同的mapper，最后将mapper数组添加到了mDevices的全局map中。后面我们以KeyboardInputMapper为例介绍key事件的传递过程。
void InputDevice::addEventHubDevice(int32_t eventHubId, bool populateMappers) {
if (mDevices.find(eventHubId) != mDevices.end()) {
return;
}
std::unique_ptr<InputDeviceContext> contextPtr(new InputDeviceContext(*this, eventHubId));
uint32_t classes = contextPtr->getDeviceClasses();
std::vector<std::unique_ptr<InputMapper>> mappers;
// Check if we should skip population
if (!populateMappers) {
mDevices.insert({eventHubId, std::make_pair(std::move(contextPtr), std::move(mappers))});
return;
}
// Switch-like devices.
if (classes & INPUT_DEVICE_CLASS_SWITCH) {
mappers.push_back(std::make_unique<SwitchInputMapper>(*contextPtr));
}
// Scroll wheel-like devices.
if (classes & INPUT_DEVICE_CLASS_ROTARY_ENCODER) {
mappers.push_back(std::make_unique<RotaryEncoderInputMapper>(*contextPtr));
}
// Vibrator-like devices.
if (classes & INPUT_DEVICE_CLASS_VIBRATOR) {
mappers.push_back(std::make_unique<VibratorInputMapper>(*contextPtr));
}
// Keyboard-like devices.
uint32_t keyboardSource = 0;
int32_t keyboardType = AINPUT_KEYBOARD_TYPE_NON_ALPHABETIC;
if (classes & INPUT_DEVICE_CLASS_KEYBOARD) {
keyboardSource |= AINPUT_SOURCE_KEYBOARD;
}
if (classes & INPUT_DEVICE_CLASS_ALPHAKEY) {
keyboardType = AINPUT_KEYBOARD_TYPE_ALPHABETIC;
}
if (classes & INPUT_DEVICE_CLASS_DPAD) {
keyboardSource |= AINPUT_SOURCE_DPAD;
}
if (classes & INPUT_DEVICE_CLASS_GAMEPAD) {
keyboardSource |= AINPUT_SOURCE_GAMEPAD;
}
if (keyboardSource != 0) {
mappers.push_back(
std::make_unique<KeyboardInputMapper>(*contextPtr, keyboardSource, keyboardType));
}
// Cursor-like devices.
if (classes & INPUT_DEVICE_CLASS_CURSOR) {
mappers.push_back(std::make_unique<CursorInputMapper>(*contextPtr));
}
// Touchscreens and touchpad devices.
if (classes & INPUT_DEVICE_CLASS_TOUCH_MT) {
mappers.push_back(std::make_unique<MultiTouchInputMapper>(*contextPtr));
} else if (classes & INPUT_DEVICE_CLASS_TOUCH) {
mappers.push_back(std::make_unique<SingleTouchInputMapper>(*contextPtr));
}
// Joystick-like devices.
if (classes & INPUT_DEVICE_CLASS_JOYSTICK) {
mappers.push_back(std::make_unique<JoystickInputMapper>(*contextPtr));
}
// External stylus-like devices.
if (classes & INPUT_DEVICE_CLASS_EXTERNAL_STYLUS) {
mappers.push_back(std::make_unique<ExternalStylusInputMapper>(*contextPtr));
}
// insert the context into the devices set
mDevices.insert({eventHubId, std::make_pair(std::move(contextPtr), std::move(mappers))});
}
回到InputDevice的process方法中，循环遍历了所有的mapper并调用其process方法，这里以KeyboardInputMapper来介绍key事件的处理过程。
void KeyboardInputMapper::process(const RawEvent* rawEvent) {
switch (rawEvent->type) {
// 如果是key事件
case EV_KEY: {
int32_t scanCode = rawEvent->code;
int32_t usageCode = mCurrentHidUsage;
mCurrentHidUsage = 0;
// 如果code为keyboard或者游戏面板对应的key
if (isKeyboardOrGamepadKey(scanCode)) {
processKey(rawEvent->when, rawEvent->value != 0, scanCode, usageCode);
}
break;
}
// 省略若干行
}
}
processKey方法中，会根据event是否为down以及event的其他属性构建出NotifyKeyArgs，然后通过getListener方法获取到InputListener，并通过其notifyKey方法将事件传递到InputDispatcher中。
void KeyboardInputMapper::processKey(nsecs_t when, bool down, int32_t scanCode, int32_t usageCode) {
int32_t keyCode;
int32_t keyMetaState;
uint32_t policyFlags;
// 省略若干行
// 根据event内容构建相应的args
NotifyKeyArgs args(getContext()->getNextId(), when, getDeviceId(), mSource, getDisplayId(),
policyFlags, down ? AKEY_EVENT_ACTION_DOWN : AKEY_EVENT_ACTION_UP,
AKEY_EVENT_FLAG_FROM_SYSTEM, keyCode, scanCode, keyMetaState, downTime);
// 获取InputListener，并调用其notifyKey方法传递key事件
getListener()->notifyKey(&args);
}
notifyKey方法中首先会构建出KeyEvent事件对象，并通过IMS传递到Java层的interceptKeyBeforeQueueing方法；然后根据args构建KeyEnvtry，并将其添加到mInboundQueue队列中；最后调用wake方法唤醒looper。
void InputDispatcher::notifyKey(const NotifyKeyArgs* args) {
// 省略若干行
// 根据args构建KeyEvent
KeyEvent event;
event.initialize(args->id, args->deviceId, args->source, args->displayId, INVALID_HMAC,
args->action, flags, keyCode, args->scanCode, metaState, repeatCount,
args->downTime, args->eventTime);
android::base::Timer t;
// 调用IMS的interceptKeyBeforeQueueing
mPolicy->interceptKeyBeforeQueueing(&event, /*byref*/ policyFlags);
// 省略若干行
// 构建KeyEntry
KeyEntry* newEntry =
new KeyEntry(args->id, args->eventTime, args->deviceId, args->source,
args->displayId, policyFlags, args->action, flags, keyCode,
args->scanCode, metaState, repeatCount, args->downTime);
// 将KeyEntry添加到mInboundQueue里面
needWake = enqueueInboundEventLocked(newEntry);
// 省略若干行
// 如果需要wake则唤醒looper
if (needWake) {
mLooper->wake();
}
}
enqueueInboundEventLocked方法中会将EventEntry添加到mInboundQueue队列中，然后如果需要wake就唤醒looper，然后就会触发threadLoop，从而调用dispatchOnce方法回到InputDispatcher中分发事件。
bool InputDispatcher::enqueueInboundEventLocked(EventEntry* entry) {
bool needWake = mInboundQueue.empty();
// 将EventEntry添加到mInboundQueue队列中
mInboundQueue.push_back(entry);
traceInboundQueueLengthLocked();
// 省略若干行
return needWake;
}
EventHub
通过前面InputReader的介绍，我们发现输入事件的源头是通过调用EventHub的getEvents方法获取的。那么，EventHub是如何创建以及进行事件的获取的呢？
EventHub获取事件
EventHub的创建
我们回到InputReader的构造方法，发现在InputReader构造方法的初始化列表中，会赋值全局变量mEventHub。
InputReader::InputReader(std::shared_ptr<EventHubInterface> eventHub,
const sp<InputReaderPolicyInterface>& policy,
const sp<InputListenerInterface>& listener)
: mContext(this),
// 初始化mEventHub
mEventHub(eventHub),
mPolicy(policy),
mGlobalMetaState(0),
mGeneration(1),
mNextInputDeviceId(END_RESERVED_ID),
mDisableVirtualKeysTimeout(LLONG_MIN),
mNextTimeout(LLONG_MAX),
mConfigurationChangesToRefresh(0) {
mQueuedListener = new QueuedInputListener(listener);
{ // acquire lock
AutoMutex _l(mLock);
refreshConfigurationLocked(0);
updateGlobalMetaStateLocked();
} // release lock
}
在初始化列表中对全局变量mEventHub进行了初始化，通过前面介绍我们知道，InputReader是在InputManager中构建出来的，那么我们继续看。
InputManager::InputManager(
const sp<InputReaderPolicyInterface>& readerPolicy,
const sp<InputDispatcherPolicyInterface>& dispatcherPolicy) {
mDispatcher = createInputDispatcher(dispatcherPolicy);
mClassifier = new InputClassifier(mDispatcher);
// 通过createInputReader创建出InputReader
mReader = createInputReader(readerPolicy, mClassifier);
}
sp<InputReaderInterface> createInputReader(const sp<InputReaderPolicyInterface>& policy,
const sp<InputListenerInterface>& listener) {
// 这里直接通过std::make_unique构建出EventHub实例
return new InputReader(std::make_unique<EventHub>(), policy, listener);
}
在InputManager中通过createInputReader构建出InputReader实例，而在createInputReader方法中，会首先通过std::make_unique构建出EventHub实例，继续看EventHub的构造函数。
EventHub::EventHub(void)
: mBuiltInKeyboardId(NO_BUILT_IN_KEYBOARD),
mNextDeviceId(1),
mControllerNumbers(),
mOpeningDevices(nullptr),
mClosingDevices(nullptr),
mNeedToSendFinishedDeviceScan(false),
mNeedToReopenDevices(false),
mNeedToScanDevices(true),
mPendingEventCount(0),
mPendingEventIndex(0),
mPendingINotify(false) {
ensureProcessCanBlockSuspend();
// 创建出epoll
mEpollFd = epoll_create1(EPOLL_CLOEXEC);
LOG_ALWAYS_FATAL_IF(mEpollFd < 0, "Could not create epoll instance: %s", strerror(errno));
// 创建inotify
mINotifyFd = inotify_init();
// 通过inotify来监听DEVICE_PATH路径（/dev/input)下的文件改变（增加或者删除）
mInputWd = inotify_add_watch(mINotifyFd, DEVICE_PATH, IN_DELETE | IN_CREATE);
// 省略若干行
struct epoll_event eventItem = {};
eventItem.events = EPOLLIN | EPOLLWAKEUP;
eventItem.data.fd = mINotifyFd;
// 将mINotifyFd添加到epoll中
int result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mINotifyFd, &eventItem);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not add INotify to epoll instance. errno=%d", errno);
// 创建管道
int wakeFds[2];
result = pipe(wakeFds);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not create wake pipe. errno=%d", errno);
mWakeReadPipeFd = wakeFds[0];
mWakeWritePipeFd = wakeFds[1];
// 设置管道读取端非阻塞属性
result = fcntl(mWakeReadPipeFd, F_SETFL, O_NONBLOCK);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake read pipe non-blocking. errno=%d",
errno);
// 设置管道写入端非阻塞属性
result = fcntl(mWakeWritePipeFd, F_SETFL, O_NONBLOCK);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake write pipe non-blocking. errno=%d",
errno);
eventItem.data.fd = mWakeReadPipeFd;
// 将读取端管道描述符添加到epoll
result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeReadPipeFd, &eventItem);
LOG_ALWAYS_FATAL_IF(result != 0, "Could not add wake read pipe to epoll instance. errno=%d",
errno);
}
在EventHub的构造方法中，我们可以看到：首先会创建出epoll，然后创建出inotify来监听/dev/input路径下文件的增删，并将inotify添加到epoll中进行监听，还会创建出一个管道，并将管道读取端也添加到epoll中。这样当有新的输入设备接入或者删除事，就会触发唤醒epoll进行处理。
EventHub如何获取输入事件
在上面介绍的InputReader中，我们了解到loopOnce方法中通过调用EventHub的getEvents来获取输入事件。那么，我们继续看getEvents方法，此方法比较长，我们先看下大概的框架。
size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) {
for (;;) {
// Reopen input devices if needed.
if (mNeedToReopenDevices) {
// 如果存在需要reopen的设备，则先关闭所有device
// 然后设置需要scan设备的标识
}
// Report any devices that had last been added/removed.
while (mClosingDevices) {
// 如果存在需要关闭的设备，则遍历所有需要关闭的设备链表，
// 删除对应的device，并构建event
}
// 需要扫描device，则调用scanDevicesLocked方法扫描
// 最后更新device列表
if (mNeedToScanDevices) {
}
//存在需要open的device，则更新mOpeningDevices链表
// 并构建event
while (mOpeningDevices != nullptr) {
}
// 需要scanFinish事件，则构建对应event
if (mNeedToSendFinishedDeviceScan) {
}
// Grab the next input event.
// 遍历需要处理的事件列表
while (mPendingEventIndex < mPendingEventCount) {
const struct epoll_event& eventItem = mPendingEventItems[mPendingEventIndex++];
if (eventItem.data.fd == mINotifyFd) {
// 如果是inotify事件，则修改对应标识，后面会扫描处理对于的变更
}
if (eventItem.data.fd == mWakeReadPipeFd) {
// 管道事件，则设置wake为true，跳出循环继续执行
}
// This must be an input event
if (eventItem.events & EPOLLIN) {
// 真正的输入事件
}
}
// 开始wait时释放锁
mLock.unlock(); // release lock before poll
// epoll等待唤醒
int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, timeoutMillis);
// 唤醒开始执行时则加锁
mLock.lock(); // reacquire lock after poll
}
// All done, return the number of events we read.
return event - buffer;
}
通过以上getEvents方法的大致流程，能够看到首先会查看是否有需要reopen的device并进行处理，接着处理需要close的device，然后是判断是否需要扫描设备并进行device扫描；接着处理新接入的设备，然后开始遍历待处理的事件，并分别处理inotify、管道以及真正的输入事件；过程中如果有event被处理则就会break掉for循环继续进行下一次处理，如果所有事件都已处理完就会走到下面的epoll_wait进入wait状态等待唤醒。
EventHub处理reopen设备
// Reopen input devices if needed.
if (mNeedToReopenDevices) {
// 设置mNeedToReopenDevices为false，避免下次循环继续处理
mNeedToReopenDevices = false;
ALOGI("Reopening all input devices due to a configuration change.");
// 关闭所有device
closeAllDevicesLocked();
// 标识需要扫描device，后面循环会进行扫描设备
mNeedToScanDevices = true;
// 跳出for循环，继续后续处理
break; // return to the caller before we actually rescan
}
处理reopen设备，首先是重置reopen标识，然后调用closeAllDevicesLocked来关闭所有的device，接着标识设备需要扫描，最后break退出此次循环，继续下一次循环处理。继续看closeAllDevicesLocked方法：
void EventHub::closeAllDevicesLocked() {
mUnattachedVideoDevices.clear();
while (mDevices.size() > 0) {
// 循环遍历所有device，并调用closeDeviceLocked来进行关闭
closeDeviceLocked(mDevices.valueAt(mDevices.size() - 1));
}
}
void EventHub::closeDeviceLocked(Device* device) {
// 省略若干行
// 从epoll移除此device的监听
unregisterDeviceFromEpollLocked(device);
// 省略若干行
// 从device列表中移除此设备
mDevices.removeItem(device->id);
// 关闭device
device->close();
// Unlink for opening devices list if it is present.
Device* pred = nullptr;
bool found = false;
// 从已经打开的device列表中查找对应的device
for (Device* entry = mOpeningDevices; entry != nullptr;) {
if (entry == device) {
found = true;
break;
}
pred = entry;
entry = entry->next;
}
// 如果找到，则从打开的device列表中将其移除
if (found) {
// Unlink the device from the opening devices list then delete it.
// We don't need to tell the client that the device was closed because
// it does not even know it was opened in the first place.
ALOGI("Device %s was immediately closed after opening.", device->path.c_str());
if (pred) {
pred->next = device->next;
} else {
mOpeningDevices = device->next;
}
// 删除对应device
delete device;
} else {
// Link into closing devices list.
// The device will be deleted later after we have informed the client.
// 打开的device列表中没找到，则将device添加到待移除的设备列表中
device->next = mClosingDevices;
mClosingDevices = device;
}
}
EventHub处理close设备
关闭device时首先从epoll中删除对应的监听并从device列表中将其移除，然后在已经打开的device列表中查找，如果找到则将其从open的device列表中移除，否则就将其添加到close的device列表中去，后面会处理close列表。这里我们继续看下epoll移除device的unregisterDeviceFromEpollLocked方法：
status_t EventHub::unregisterDeviceFromEpollLocked(Device* device) {
if (device->hasValidFd()) {
// 如果设备存在有效的fd，则调用unregisterFdFromEpoll将其从epoll中移除
status_t result = unregisterFdFromEpoll(device->fd);
}
return OK;
}
status_t EventHub::unregisterFdFromEpoll(int fd) {
// 调用epoll_ctl并传递EPOLL_CTL_DEL的flag将fd从epoll中移除
if (epoll_ctl(mEpollFd, EPOLL_CTL_DEL, fd, nullptr)) {
ALOGW("Could not remove fd from epoll instance: %s", strerror(errno));
return -errno;
}
return OK;
}
接着我们继续看getEvents中对带关闭设备的处理过程：
// Report any devices that had last been added/removed.
// 遍历所有需要关闭的device链表
while (mClosingDevices) {
Device* device = mClosingDevices;
ALOGV("Reporting device closed: id=%d, name=%s\n", device->id, device->path.c_str());
// 移动表头到到下一个位置
mClosingDevices = device->next;
// 构建设备移除的event
event->when = now;
event->deviceId = (device->id == mBuiltInKeyboardId)
? ReservedInputDeviceId::BUILT_IN_KEYBOARD_ID
: device->id;
event->type = DEVICE_REMOVED;
event += 1;
// 删除对于device
delete device;
// 标识需要构建扫描完成的条件
mNeedToSendFinishedDeviceScan = true;
}
处理关闭的device，首先是遍历整个需要关闭的device链表，并依次对每一个device，构造设备移除的event，然后删除对应的device，最后标识需要构建扫描完成的事件条件，待后面添加扫描完成的event。
EventHub扫描设备
前面如果有处理reopen设备，则会关闭所有设备，并设置需要扫描设备的标识，然后这里会调用scanDevicesLocked方法来扫描device。
if (mNeedToScanDevices) {
// 重置需要扫描的标识，避免下一次继续扫描设备
mNeedToScanDevices = false;
// 开始扫描设备
scanDevicesLocked();
// 标识后面需要有扫描完成的event
mNeedToSendFinishedDeviceScan = true;
}
扫描设备会调用scanDevicesLocked方法进行扫描处理，我们继续看：
void EventHub::scanDevicesLocked() {
// 继续调用scanDirLocked来扫描设备，这里传入的路径为/dev/input
status_t result = scanDirLocked(DEVICE_PATH);
if (result < 0) {
ALOGE("scan dir failed for %s", DEVICE_PATH);
}
// 省略若干行
// 如果存在虚拟的键盘，则在这里创建虚拟键盘
if (mDevices.indexOfKey(ReservedInputDeviceId::VIRTUAL_KEYBOARD_ID) < 0) {
createVirtualKeyboardLocked();
}
}
首先调用scanDirLocked扫描/dev/input目录来索引可用的device，然后判断如果存在虚拟的键盘，则调用createVirtualKeyboardLocked方法来创建虚拟键盘设备。
status_t EventHub::scanDirLocked(const char* dirname) {
char devname[PATH_MAX];
char* filename;
DIR* dir;
struct dirent* de;
// 打开/dev/input目录
dir = opendir(dirname);
if (dir == nullptr) return -1;
strcpy(devname, dirname);
filename = devname + strlen(devname);
*filename++ = '/';
// 遍历/dev/input目录
while ((de = readdir(dir))) {
if (de->d_name[0] == '.' &&
(de->d_name[1] == '\0' || (de->d_name[1] == '.' && de->d_name[2] == '\0')))
continue;
strcpy(filename, de->d_name);
// 如果文件名有效，则打开对于device
openDeviceLocked(devname);
}
// 关闭目录
closedir(dir);
return 0;
}
扫描device主要是扫描/dev/input目录，遍历每一个设备文件并调用openDeviceLocked方法来打开对应的device，最后关闭目录。
status_t EventHub::openDeviceLocked(const char* devicePath) {
char buffer[80];
ALOGV("Opening device: %s", devicePath);
// 打开device文件
int fd = open(devicePath, O_RDWR | O_CLOEXEC | O_NONBLOCK);
// 省略若干行
// 然后依次获取设备的名称、驱动版本、设备的厂商等信息、物理路径、唯一的id等信息
// 接着判断是键盘或者游戏面板、鼠标等设备类型进行特殊处理
// 最后将设备添加到epoll中进行监听
if (registerDeviceForEpollLocked(device) != OK) {
// 添加失败则删除设备并退出
delete device;
return -1;
}
// 省略若干行
// 将设备添加到device列表
addDeviceLocked(device);
return OK;
}
openDeviceLocked方法中，首先通过open方法打开对应的设备文件，然后会获取设备的各种信息并进行相应的处理，接着通过registerDeviceForEpollLocked方法将device添加到epoll中去，最后再通过addDeviceLocked方法将device添加到设备列表当中去。
status_t EventHub::registerDeviceForEpollLocked(Device* device) {
// 省略若干行
// 调用registerFdForEpoll将设备描述符添加到epoll中去
status_t result = registerFdForEpoll(device->fd);
// 省略若干行
return result;
}
status_t EventHub::registerFdForEpoll(int fd) {
// TODO(b/121395353) - consider adding EPOLLRDHUP
struct epoll_event eventItem = {};
// 设置event类型为EPOLLIN 和 EPOLLWAKEUP
eventItem.events = EPOLLIN | EPOLLWAKEUP;
eventItem.data.fd = fd;
// 通过epoll_ctl调用并传入EPOLL_CTL_ADD的flag添加对应fd到epoll中
if (epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, &eventItem)) {
ALOGE("Could not add fd to epoll instance: %s", strerror(errno));
return -errno;
}
return OK;
}
void EventHub::addDeviceLocked(Device* device) {
// 将设备添加到device列表中
mDevices.add(device->id, device);
// 将device添加到open的设备链表中
device->next = mOpeningDevices;
mOpeningDevices = device;
}
我们能够看到在registerFdForEpoll方法中，设备的fd被添加为EPOLLIN和EPOLLWAKEUP类型的，所以这两种类型的事件到来时就可以唤醒epoll工作，然后在addDeviceLocked方法中会将设备添加到device列表和open的device链表中去。
EventHub处理open设备
在getEvents方法中，会遍历整个open的设备链表，迭代每个设备，然后构建设备添加的event，最后标识扫描完成的变量；如果在处理过程中，buffer已经满了，则会break掉，未处理的设备会在下一次迭代时继续处理。
// 迭代每一个open的device
while (mOpeningDevices != nullptr) {
Device* device = mOpeningDevices;
ALOGV("Reporting device opened: id=%d, name=%s\n", device->id, device->path.c_str());
// 修改头指针
mOpeningDevices = device->next;
// 构建DEVICE_ADDED的event
event->when = now;
event->deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;
event->type = DEVICE_ADDED;
event += 1;
// 设置scan完成标识
mNeedToSendFinishedDeviceScan = true;
// buffer满了，则跳出
if (--capacity == 0) {
break;
}
}
EventHub处理event
// 迭代处理所有event
while (mPendingEventIndex < mPendingEventCount) {
const struct epoll_event& eventItem = mPendingEventItems[mPendingEventIndex++];
if (eventItem.data.fd == mINotifyFd) {
// event为device变更，则标识mPendingINotify，后面会进行处理
if (eventItem.events & EPOLLIN) {
mPendingINotify = true;
} else {
ALOGW("Received unexpected epoll event 0x%08x for INotify.", eventItem.events);
}
continue;
}
// event是wake管道消息
if (eventItem.data.fd == mWakeReadPipeFd) {
if (eventItem.events & EPOLLIN) {
ALOGV("awoken after wake()");
// 标识被唤醒，后面epoll就不会进入wait状态
awoken = true;
char buffer[16];
ssize_t nRead;
do {// 从管道中读取出消息内容
nRead = read(mWakeReadPipeFd, buffer, sizeof(buffer));
} while ((nRead == -1 && errno == EINTR) || nRead == sizeof(buffer));
} else {
ALOGW("Received unexpected epoll event 0x%08x for wake read pipe.",
eventItem.events);
}
continue;
}
// 通过event中的设备描述符获取对应device
Device* device = getDeviceByFdLocked(eventItem.data.fd);
// 省略若干行
// This must be an input event
if (eventItem.events & EPOLLIN) {
// event是input事件
// 从device中读取出事件内容
int32_t readSize =
read(device->fd, readBuffer, sizeof(struct input_event) * capacity);
if (readSize == 0 || (readSize < 0 && errno == ENODEV)) {
// Device was removed before INotify noticed.
ALOGW("could not get event, removed? (fd: %d size: %" PRId32
" bufferSize: %zu capacity: %zu errno: %d)\n",
device->fd, readSize, bufferSize, capacity, errno);
// 出错，则关闭对应device，并标识设备发生变更
deviceChanged = true;
closeDeviceLocked(device);
}
// 省略若干行
else {
// 获取deviceId
int32_t deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;
// 遍历读取到的所有event，并构建出RawEvent
size_t count = size_t(readSize) / sizeof(struct input_event);
for (size_t i = 0; i < count; i++) {
struct input_event& iev = readBuffer[i];
event->when = processEventTimestamp(iev);
event->deviceId = deviceId;
event->type = iev.type;
event->code = iev.code;
event->value = iev.value;
event += 1;
capacity -= 1;
}
// 如果buffer满了，则break掉
if (capacity == 0) {
// The result buffer is full. Reset the pending event index
// so we will try to read the device again on the next iteration.
mPendingEventIndex -= 1;
break;
}
}
}
}
这里处理event时，首先处理设备的变更事件，然后会处理wake管道事件，最后才会处理真正的input事件；处理input事件时会遍历每一个获取到的event，并构建出对应的RawEvent。
EventHub处理inotify事件
// readNotify() will modify the list of devices so this must be done after
// processing all other events to ensure that we read all remaining events
// before closing the devices.
if (mPendingINotify && mPendingEventIndex >= mPendingEventCount) {
// 标识已经处理过
mPendingINotify = false;
// 处理inotify事件
readNotifyLocked();
deviceChanged = true;
}
status_t EventHub::readNotifyLocked() {
// 省略若干行
// 从mINotifyFd读取事件内容
res = read(mINotifyFd, event_buf, sizeof(event_buf));
// 省略若干行
// 遍历每一个inotify_event
while (res >= (int)sizeof(*event)) {
event = (struct inotify_event*)(event_buf + event_pos);
if (event->len) {
if (event->wd == mInputWd) {
// 是input类型的变更
// 获取设备对应的文件路径
std::string filename = StringPrintf("%s/%s", DEVICE_PATH, event->name);
if (event->mask & IN_CREATE) {
// 是设备连入事件，则调用openDeviceLocked来添加设备
// 上面已经介绍过，这里就不展开了
openDeviceLocked(filename.c_str());
} else {
// 否则是设备断开事件，则调用closeDeviceByPathLocked关闭设备
ALOGI("Removing device '%s' due to inotify event\n", filename.c_str());
closeDeviceByPathLocked(filename.c_str());
}
}
// 省略若干行
}
event_size = sizeof(*event) + event->len;
res -= event_size;
event_pos += event_size;
}
return 0;
}
这里首先会从mINotifyFd读取对应的inotify事件，然后遍历每一个event，判断是设备接入还是断开并分别进行设备添加和移除的处理。
void EventHub::closeDeviceByPathLocked(const char* devicePath) {
// 从device列表中根据设备路径查找device
Device* device = getDeviceByPathLocked(devicePath);
if (device) {
// 找到则调用closeDeviceLocked来关闭device
// 上面reopen时已经介绍过，这里不再展开
closeDeviceLocked(device);
return;
}
ALOGV("Remove device: %s not found, device may already have been removed.", devicePath);
}
EventHub::Device* EventHub::getDeviceByPathLocked(const char* devicePath) const {
// 遍历整个device列表
for (size_t i = 0; i < mDevices.size(); i++) {
Device* device = mDevices.valueAt(i);
// 根据设备路径配备device
if (device->path == devicePath) {
return device;
}
}
return nullptr;
}
这里关闭设备，首先是通过设备的路径从device列表中查找对应的device，如果找到了，则调用closeDeviceLocked去处理设备的关闭。
小结
通过以上介绍，我们可以了解到EventHub的创建过程以及其采用epoll加inotify的方式来实现input设备以及input事件的监听；另外，在getEvents方法中，包含了整个设备的添加、删除以及input事件的处理，而这些事件的处理正是基于EventHub创建时采用的epoll加inotify机制实现的。
