Android Input子系统 -- EventHub

前言

前面其实也有提到EventHub的构造函数，里面就是创建epoll实例，然后把一些事件触发的文件描述符加入到epoll里面统一管理。

• 监控/dev/input/目录的iNotify文件mINotifyFd
• 接收Kernel驱动事件(/dev/input/eventX)的文件描述符
• 用来唤醒InputReader线程的管道读文件

EventHub是服务于InputReader线程的，前面在InputRead的构造函数里面有创建EventHub的实例。

InputReader线程

InputReader线程主要就是查看threadLoop接口中代码的实现，threadLoop返回值是true代表的是会不断的循环，返回false的话就不会继续在调用threadLoop函数。

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bool InputReaderThread::threadLoop() { mReader->loopOnce(); return true; }

不停的调用InputReader的loopOnce函数

loopOnce函数

InputReader.cpp

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void InputReader::loopOnce() { ... { AutoMutex _l(mLock); uint32_t changes = mConfigurationChangesToRefresh; if (changes) { timeoutMillis = 0; ... } else if (mNextTimeout != LLONG_MAX) { nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC); timeoutMillis = toMillisecondTimeoutDelay(now, mNextTimeout); } } //从EventHub读取事件，其中EVENT_BUFFER_SIZE = 256 size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE); { // acquire lock AutoMutex _l(mLock); mReaderIsAliveCondition.broadcast(); if (count) { //处理事件 processEventsLocked(mEventBuffer, count); } if (oldGeneration != mGeneration) { inputDevicesChanged = true; getInputDevicesLocked(inputDevices); } ... } // release lock if (inputDevicesChanged) { //输入设备发生改变 mPolicy->notifyInputDevicesChanged(inputDevices); } //发送事件到nputDispatcher mQueuedListener->flush(); }

两个关键的地方，从注释可以很明确的看出来，首先是获取到底层的input事件，处理事件，然后发送到InputDispatcher线程

• mEventHub->getEvents
• processEventsLocked(mEventBuffer, count)
• mQueuedListener->flush

EventHub->getEvents

EventHub.cpp

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size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) { AutoMutex _l(mLock); //加锁 struct input_event readBuffer[bufferSize]; RawEvent* event = buffer; //原始事件 size_t capacity = bufferSize; //容量大小为256 bool awoken = false; for (;;) { nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC); ... if (mNeedToScanDevices) { mNeedToScanDevices = false; scanDevicesLocked(); //扫描设备 mNeedToSendFinishedDeviceScan = true; } while (mOpeningDevices != NULL) { Device* device = mOpeningDevices; mOpeningDevices = device->next; event->when = now; event->deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id; event->type = DEVICE_ADDED; //添加设备的事件 event += 1; mNeedToSendFinishedDeviceScan = true; if (--capacity == 0) { break; } } ... bool deviceChanged = false; while (mPendingEventIndex < mPendingEventCount) { //从mPendingEventItems读取事件项 const struct epoll_event& eventItem = mPendingEventItems[mPendingEventIndex++]; ... //获取设备ID所对应的device ssize_t deviceIndex = mDevices.indexOfKey(eventItem.data.u32); Device* device = mDevices.valueAt(deviceIndex); if (eventItem.events & EPOLLIN) { //从设备不断读取事件，放入到readBuffer int32_t readSize = read(device->fd, readBuffer, sizeof(struct input_event) * capacity); if (readSize == 0 || (readSize < 0 && errno == ENODEV)) { deviceChanged = true; closeDeviceLocked(device);//设备已被移除则执行关闭操作 } else if (readSize < 0) { ... } else if ((readSize % sizeof(struct input_event)) != 0) { ... } else { int32_t deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id; size_t count = size_t(readSize) / sizeof(struct input_event); for (size_t i = 0; i < count; i++) { //获取readBuffer的数据 struct input_event& iev = readBuffer[i]; //将input_event信息, 封装成RawEvent event->when = nsecs_t(iev.time.tv_sec) * 1000000000LL + nsecs_t(iev.time.tv_usec) * 1000LL; event->deviceId = deviceId; event->type = iev.type; event->code = iev.code; event->value = iev.value; event += 1; capacity -= 1; } if (capacity == 0) { mPendingEventIndex -= 1; break; } } } ... } ... mLock.unlock(); //poll之前先释放锁 //等待input事件的到来 int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, timeoutMillis); ... mLock.lock(); //poll之后再次请求锁 if (pollResult < 0) { //出现错误 mPendingEventCount = 0; if (errno != EINTR) { usleep(100000); //系统发生错误则休眠1s } } else { mPendingEventCount = size_t(pollResult); } } return event - buffer; //返回所读取的事件个数 }

虽然精简了代码还是比较长，主要是以下几点：

• EventHub是采用了INotify和epoll机制监听目录/dev/input下设备节点，当有IO事件，会通过epoll_wait返回事件的详细信息
• 当epoll_wait被返回有IO数据的时候，通过read函数读取input事件的数据
• 把input_event结构体转化为RawEvent事件

InputEventReader.h

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struct input_event { struct timeval time; //事件发生的时间点 __u16 type; __u16 code; __s32 value; }; struct RawEvent { nsecs_t when; //事件发生的时间店 int32_t deviceId; //产生事件的设备Id int32_t type; // 事件类型 int32_t code; int32_t value; };

事件类型：

1. DEVICE_ADD
2. DEVICE_REMOVED
3. FINISHED_DEVICE_SCAN
4. type

InputReader->processEventsLocked

InputReader.cpp

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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; //同一设备的事件打包处理 } //数据事件的处理 processEventsForDeviceLocked(deviceId, rawEvent, batchSize); } else { switch (rawEvent->type) { case EventHubInterface::DEVICE_ADDED: //设备添加 addDeviceLocked(rawEvent->when, rawEvent->deviceId); break; case EventHubInterface::DEVICE_REMOVED: //设备移除 removeDeviceLocked(rawEvent->when, rawEvent->deviceId); break; case EventHubInterface::FINISHED_DEVICE_SCAN: //设备扫描完成 handleConfigurationChangedLocked(rawEvent->when); break; default: ALOG_ASSERT(false);//不会发生 break; } } count -= batchSize; rawEvent += batchSize; } }

主要是根据不同的事件类型做不同的处理，我们比较关注对数据的处理，主要是看这个函数processEventsForDeviceLocked

事件处理 processEventsForDeviceLocked

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void InputReader::processEventsForDeviceLocked(int32_t deviceId, const RawEvent* rawEvents, size_t count) { ssize_t deviceIndex = mDevices.indexOfKey(deviceId); ... InputDevice* device = mDevices.valueAt(deviceIndex); if (device->isIgnored()) { return; //可忽略则直接返回 } //调用对应设备的process函数 device->process(rawEvents, count); }

通过deviceId来获取合适的InputDevice，InputDevice是当检测到/dev/input/下有设备节点添加的时候创建的

调用对应的device的process函数

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void InputDevice::process(const RawEvent* rawEvents, size_t count) { size_t numMappers = mMappers.size(); for (const RawEvent* rawEvent = rawEvents; count--; rawEvent++) { if (mDropUntilNextSync) { if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) { mDropUntilNextSync = false; } } else if (rawEvent->type == EV_SYN && rawEvent->code == SYN_DROPPED) { mDropUntilNextSync = true; reset(rawEvent->when); } else { for (size_t i = 0; i < numMappers; i++) { InputMapper* mapper = mMappers[i]; //调用具体mapper来处理 mapper->process(rawEvent); } } } }

这里处理输入事件主要是把Linux下发送过来的RawEvent转化为Android 的Key Event和Key Code，在Android中不同的输入设备对应不同的Key Layout文件，这里就是选择对应的kl文件来处理。

下面专门针对按键的事件处理跟一下流程。

按键事件处理流程

InputReader.cpp

KeyBoardInputMapper->process

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void KeyboardInputMapper::process(const RawEvent* rawEvent) { switch (rawEvent->type) { case EV_KEY: { int32_t scanCode = rawEvent->code; int32_t usageCode = mCurrentHidUsage; mCurrentHidUsage = 0; if (isKeyboardOrGamepadKey(scanCode)) { int32_t keyCode; //获取所对应的KeyCode if (getEventHub()->mapKey(getDeviceId(), scanCode, usageCode, &keyCode, &flags)) { keyCode = AKEYCODE_UNKNOWN; flags = 0; } // processKey(rawEvent->when, rawEvent->value != 0, keyCode, scanCode, flags); } break; } case EV_MSC: ... case EV_SYN: ... } }

通过mapKey函数获取对应scanCode的Android Key Code

EventHub.cpp

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status_t EventHub::mapKey(int32_t deviceId, int32_t scanCode, int32_t usageCode, int32_t metaState, int32_t* outKeycode, int32_t* outMetaState, uint32_t* outFlags) const { AutoMutex _l(mLock); Device* device = getDeviceLocked(deviceId); //获取设备对象 status_t status = NAME_NOT_FOUND; if (device) { sp kcm = device->getKeyCharacterMap(); if (kcm != NULL) { //根据scanCode找到keyCode if (!kcm->mapKey(scanCode, usageCode, outKeycode)) { *outFlags = 0; status = NO_ERROR; } } } ... return status; }

真正干活做转换的是KeyCharacterMap::mapKey函数。

InputReader.cpp

InputMapper->processKey

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void KeyboardInputMapper::processKey(nsecs_t when, bool down, int32_t keyCode, int32_t scanCode, uint32_t policyFlags) { if (down) { if (mParameters.orientationAware && mParameters.hasAssociatedDisplay) { keyCode = rotateKeyCode(keyCode, mOrientation); } ssize_t keyDownIndex = findKeyDown(scanCode); if (keyDownIndex >= 0) { //mKeyDowns记录着所有按下的键 keyCode = mKeyDowns.itemAt(keyDownIndex).keyCode; } else { ... mKeyDowns.push(); //压入栈顶 KeyDown& keyDown = mKeyDowns.editTop(); keyDown.keyCode = keyCode; keyDown.scanCode = scanCode; } mDownTime = when; //记录按下时间点 } else { ssize_t keyDownIndex = findKeyDown(scanCode); if (keyDownIndex >= 0) { //键抬起操作，则移除按下事件 keyCode = mKeyDowns.itemAt(keyDownIndex).keyCode; mKeyDowns.removeAt(size_t(keyDownIndex)); } else { return; //键盘没有按下操作，则直接忽略抬起操作 } } nsecs_t downTime = mDownTime; ... //创建NotifyKeyArgs对象, when记录eventTime, downTime记录按下时间； NotifyKeyArgs args(when, getDeviceId(), mSource, policyFlags, down ? AKEY_EVENT_ACTION_DOWN : AKEY_EVENT_ACTION_UP, AKEY_EVENT_FLAG_FROM_SYSTEM, keyCode, scanCode, newMetaState, downTime); //通知key事件 getListener()->notifyKey(&args); }

• mKeyDowns记录着所有按下的键
• mDownTime记录按下时间点
• KeyboardInputMapper的mContext指向InputReader，getListener()获取mQueuedListener，然后调用notifyKey接口

InputListener.cpp

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void QueuedInputListener::notifyKey(const NotifyKeyArgs* args) { mArgsQueue.push(new NotifyKeyArgs(*args)); }

把事件放入向量mArgsQueue，然后就是把事件发送给InputDispatcher线程了

发送事件 QueuedInputListener->flush

InputListener.cpp

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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(); }

遍历刚才的向量，调用对应的notify接口，NotifyArgs的实现子类包含：

• NotifyConfigurationChangedArgs
• NotifyKeyArgs
• NotifyMotionArgs
• NotifySwitchArgs
• NotifyDeviceResetArgs

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void NotifyKeyArgs::notify(const sp& listener) const { listener->notifyKey(this); // this是指NotifyKeyArgs }

InputDispatcher.cpp

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void InputDispatcher::notifyKey(const NotifyKeyArgs* args) { if (!validateKeyEvent(args->action)) { return; } ... int32_t keyCode = args->keyCode; if (keyCode == AKEYCODE_HOME) { if (args->action == AKEY_EVENT_ACTION_DOWN) { property_set("sys.domekey.down", "1"); } else if (args->action == AKEY_EVENT_ACTION_UP) { property_set("sys.domekey.down", "0"); } } if (metaState & AMETA_META_ON && args->action == AKEY_EVENT_ACTION_DOWN) { ... } else if (args->action == AKEY_EVENT_ACTION_UP) { ... } KeyEvent event; //初始化KeyEvent对象 event.initialize(args->deviceId, args->source, args->action, flags, keyCode, args->scanCode, metaState, 0, args->downTime, args->eventTime); //mPolicy是指NativeInputManager对象。 mPolicy->interceptKeyBeforeQueueing(&event, /*byref*/ policyFlags); bool needWake; { mLock.lock(); if (shouldSendKeyToInputFilterLocked(args)) { mLock.unlock(); policyFlags |= POLICY_FLAG_FILTERED; //当inputEventObj不为空, 则事件被filter所拦截 if (!mPolicy->filterInputEvent(&event, policyFlags)) { return; } mLock.lock(); } int32_t repeatCount = 0; //创建KeyEntry对象 KeyEntry* newEntry = new KeyEntry(args->eventTime, args->deviceId, args->source, policyFlags, args->action, flags, keyCode, args->scanCode, metaState, repeatCount, args->downTime); //将KeyEntry放入队列 needWake = enqueueInboundEventLocked(newEntry); mLock.unlock(); } if (needWake) { //唤醒InputDispatcher线程 mLooper->wake(); } }

主要完成以下几个事情：

• 调用NativeInputManager.interceptKeyBeforeQueueing，加入队列前执行拦截动作，但并不改变流程
  • ​ IMS.interceptKeyBeforeQueueing
  • ​ InputMonitor.interceptKeyBeforeQueueing（继承IMS.WindowManagerCallbacks）
  • ​ PhoneWindowManager.interceptKeyBeforeQueueing（继承WindowManagerPolicy）
• 当mInputFilterEnabled=true（该值默认为false，可通过setInputFilterEnabled设置），则调用NativeInputManager.filterInputEvent过滤输入事件
  • ​ 当返回值为false则过滤事件，不往下发
• 生成KeyEvent，并调用enqueueInboundEventLocked，把事件加入到InputDispatchered的成员变量mInboundQueue。
• 唤醒InputDispatcher线程

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void Looper::wake() { uint64_t inc = 1; ssize_t nWrite = TEMP_FAILURE_RETRY(write(mWakeEventFd, &inc, sizeof(uint64_t))); if (nWrite != sizeof(uint64_t)) { if (errno != EAGAIN) { ALOGW("Could not write wake signal, errno=%d", errno); } } }

InputDispatcher线程主要是用来跟JAVA层的IMS和WMS通信的，给JAVA层IMS上报输入事件，找到对应的Window。

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