Android(安卓)Input流程

一.input 系统初始化

安卓系统启动时,会开启SystemServer进程,SystemServer执行main函数,调用startOtherService()初始化windowManagerService和InputManagerService等
InputManagerService的构造函数如下,mPtr是一个指向nativeInputManager对象的指针.

        mPtr = nativeInit(this, mContext, mHandler.getLooper().getQueue());        LocalServices.addService(InputManagerInternal.class, new LocalService());

这里的nativeInit方法调用到com_android_server_input_InputManagerService.cpp中NativeInputManager的构造函数
这里会构造一个EventHub对象并将它传入InputManager的构造函数中,

321    sp eventHub = new EventHub();322    mInputManager = new InputManager(eventHub, this, this);

27InputManager::InputManager(28        const sp& eventHub,29        const sp& readerPolicy,30        const sp& dispatcherPolicy) {31    mDispatcher = new InputDispatcher(dispatcherPolicy);32    mReader = new InputReader(eventHub, readerPolicy, mDispatcher);33    initialize();34}

initialize函数中会设置两个线程来运行InputReader和InputDispatcher

49    mReaderThread = new InputReaderThread(mReader);50    mDispatcherThread = new InputDispatcherThread(mDispatcher);

inputManagerService会设置一个回调,供windowManager调用,之后会调用inputManager的start()方法

wm = WindowManagerService.main(context, inputManager,                    mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,                    !mFirstBoot, mOnlyCore);inputManager.setWindowManagerCallbacks(wm.getInputMonitor());inputManager.start();

start方法会最终调用到InputManager.cpp 文件中的 status_t InputManager::start()函数
主要步骤如下,运行dispatcherThread的run()方法和mReaderThread的run()方法.

54    status_t result = mDispatcherThread->run("InputDispatcher", PRIORITY_URGENT_DISPLAY);55    if (result) {56        ALOGE("Could not start InputDispatcher thread due to error %d.", result);57        return result;58    }5960    result = mReaderThread->run("InputReader", PRIORITY_URGENT_DISPLAY);61    if (result) {62        ALOGE("Could not start InputReader thread due to error %d.", result);6364        mDispatcherThread->requestExit();65        return result;66    }6768    return OK;

新建位图图像.jpg

二.读取input events

mReaderThread->run()方法会调用自身的 threadLoop()方法,进而调用mReader的loopOnce()方法,
loopOnce()方法主要分为三个主要的步骤.

步骤一:

在该方法中会通过EventHub来获取input事件,计算缓冲区大小,判断是否有新的事件产生,然后用processEventsLocked()方法来处理events

 size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE);314        if (count) {315            processEventsLocked(mEventBuffer, count);316        }

步骤二:

在processEventsLocked()方法中会调用processEventsForDeviceLocked(deviceId, rawEvent, batchSize)函数,该函数会确定设备编号并调用

531    device->process(rawEvents, count);

安卓系统中每种输入设备都对应了一种Mapper,比如SwitchInputMapper, VibratorInputMapper,KeyBoardInputMapper

在process()函数中会调用对应mapper的processKey()函数,在该函数中具体处理不同的input事件

在processKey()函数中会调用 getListener()->notifyKey(), 也就是调用mQueuedListener.notifyKey();

而这个listener的notifyKey()方法只有一行代码,将notifyKeyArgs对象放入到mArgsQueue队列中.

mArgsQueue.push(**new** NotifyKeyArgs(*args));

步骤三:

最后一步会将mQueuedListener队列中的所有内容全部清空.

mQueuedListener->flush();

flush()函数中将所有的NotifyArgs对象取出,依次执行args->notify()

171void QueuedInputListener::flush() {172    size_t count = mArgsQueue.size();173    for (size_t i = 0; i < count; i++) {174        NotifyArgs* args = mArgsQueue[i];175        args->notify(mInnerListener);176        delete args;177    }178    mArgsQueue.clear();179}

而notify()函数会调用innnerListener的notifyKey()函数,innerListener实际上就是构造InputReader时传入的InputDispatcher,所以调用的就是InputDispatcher的notifyKey()函数

62void NotifyKeyArgs::notify(const sp& listener) const {63    listener->notifyKey(this);64}

在notifyKey()函数中会新建一个KeyEvent对象并进行初始化,然后调用mPolicy的interceptKeyBeforeQueueing__(mPolicy就是NativeInputManagers)

2548    KeyEvent event;2549    event.initialize(args->deviceId, args->source, args->action,2550            flags, keyCode, args->scanCode, metaState, 0,2551            args->downTime, args->eventTime);25522553    mPolicy->interceptKeyBeforeQueueing(&event, /*byref*/ policyFlags);

这里会在c++代码中调用java层的代码,会先把keyEvent转换为jobject对象，然后调用java层对应的interceptBeforeQueueing函数

894        jobject keyEventObj = android_view_KeyEvent_fromNative(env, keyEvent);896        if (keyEventObj) {897            wmActions = env->CallIntMethod(mServiceObj,898                    gServiceClassInfo.interceptKeyBeforeQueueing,899                    keyEventObj, policyFlags);

这里调用了native的interceptKeyBeforeQueueing函数,用到了在初始化时设定的一个windowManager持有的回调.

        // Native callback.        private int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {            return mWindowManagerCallbacks.interceptKeyBeforeQueueing(event, policyFlags);        }

通过这个windowManager持有的回调，最终会调用到WindowPhoneManager的interceptKeyBeforeQueueing函数(mpolicy就是windowPhoneManager),这样以来对input的管理最终集中到了windowManager中.

    /* Provides an opportunity for the window manager policy to intercept early key     * processing as soon as the key has been read from the device. */    @Override    public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {        return mService.mPolicy.interceptKeyBeforeQueueing(event, policyFlags);    }

input events从java层的windowManagerService的拦截函数返回后,会继续在notify()函数中运行,这里会继续判断是否打开了过滤器开关,如果打开了就对event进行过滤,并返回

2559        if (shouldSendKeyToInputFilterLocked(args)) {2560            mLock.unlock();25612562            policyFlags |= POLICY_FLAG_FILTERED;2563            if (!mPolicy->filterInputEvent(&event, policyFlags)) {2564                return; // event was consumed by the filter2565            }25662567            mLock.lock();2568        }

将event信息存储在一个KeyEntry对象中,调用enqueueInboundEventLocked函数并判断是否需要唤醒

2571        KeyEntry* newEntry = new KeyEntry(args->eventTime,2572                args->deviceId, args->source, policyFlags,2573                args->action, flags, keyCode, args->scanCode,2574                metaState, repeatCount, args->downTime);25752576        needWake = enqueueInboundEventLocked(newEntry);

之后如果需要唤醒,就会调用mLooper.wake()唤醒分发线程进行事件分发.

三.分发events到UI窗口

回到InputDispatcher中分析:
mDispatcherThread::threadLoop()方法中会调用dispatchOnce()函数,该函数中主要调用两个方法一个是
DispatchOnceInnerLocked()函数.

319        if (!haveCommandsLocked()) {320            dispatchOnceInnerLocked(&nextWakeupTime);321        }

主要会调用到pokeUserActivityLocked()函数

394        // Poke user activity for this event.395        if (mPendingEvent->policyFlags & POLICY_FLAG_PASS_TO_USER) {396            pokeUserActivityLocked(mPendingEvent);397        }

在 pokeUserActivityLocked()函数中会将key事件封装成系统需要处理的key事件.

1902    CommandEntry* commandEntry = postCommandLocked(1903            & InputDispatcher::doPokeUserActivityLockedInterruptible);1904    commandEntry->eventTime = eventEntry->eventTime;1905    commandEntry->userActivityEventType = eventType;

在这里会调用 doPokeUserActivityLockedInterruptible函数,函数中会调用NativeInputManager的pokeUserActivity函数

mPolicy->pokeUserActivity(commandEntry->eventTime, commandEntry->userActivityEventType);

通过JNI调用到java层PowerManagerService中的 userActivityFromNative函数,

106        env->CallVoidMethod(gPowerManagerServiceObj,107                gPowerManagerServiceClassInfo.userActivityFromNative,108                nanoseconds_to_milliseconds(eventTime), eventType, 0);

    private void userActivityInternal(long eventTime, int event, int flags, int uid) {        synchronized (mLock) {            if (userActivityNoUpdateLocked(eventTime, event, flags, uid)) {                updatePowerStateLocked();            }        }    }

回到dispatchOnceInnerLocked函数之后会对event的类型进行判断,按照event的类型进行不同的操作.
首先会调用 findFocusedWindowTargetLocked函数得到要对应的UI窗口

875    int32_t injectionResult = findFocusedWindowTargetsLocked(currentTime,876            entry, inputTargets, nextWakeupTime);

如果是按键事件,会调用dispatchKeyLocked()函数,又会调用dispatchEventLocked()函数：
确定对应输出的UI窗口,并得到它们之间的connection.

1029        const InputTarget& inputTarget = inputTargets.itemAt(i);10301031        ssize_t connectionIndex = getConnectionIndexLocked(inputTarget.inputChannel);

之后会调用prepareDispatchCycleLocked函数

之后会进入到enqueueDispatchEntriesLocked函数中.

1945            enqueueDispatchEntriesLocked(currentTime, connection,1946                    splitMotionEntry, inputTarget);1947            splitMotionEntry->release();

connection中维护一个outboundQueue队列,这个队列中存储input与该window之间的事件.
如果队列为空,就开始循环分发.

1974    // If the outbound queue was previously empty, start the dispatch cycle going.1975    if (wasEmpty && !connection->outboundQueue.isEmpty()) {1976        startDispatchCycleLocked(currentTime, connection);1977    }

在startDisplayCycleLocked函数中：
会不断地取出事件进行分发,具体的分发过程利用到了linux的epoll机制,后面有具体分析.

 status = connection->inputPublisher.publishMotionEvent

操作完成后会释放掉pendingEvent

478    if (done) {479        if (dropReason != DROP_REASON_NOT_DROPPED) {480            dropInboundEventLocked(mPendingEvent, dropReason);481        }482        mLastDropReason = dropReason;483484        releasePendingEventLocked();485        *nextWakeupTime = LONG_LONG_MIN;  // force next poll to wake up immediately486    }

Looper利用epoll机制接收events,并调用callback回调的handleEvent方法.也就是NativeInputEventReceiver的handleEvent() 方法

361            // Invoke the callback.  Note that the file descriptor may be closed by362            // the callback (and potentially even reused) before the function returns so363            // we need to be a little careful when removing the file descriptor afterwards.364            int callbackResult = response.request.callback->handleEvent(fd, events, data);

而为什么会调用到这个InputEventReciever呢,InputEventReceiver是在ViewRootImpl中的setView()方法中被声明的,它的构造函数中有两个变量: mInputChannel和 Looper.myLooper()

mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,        Looper.myLooper());

而在InputEventReceiver的构造函数中,会先取得主线程的looper对象和client端的java层inputChannel对象,然后调用NativeInit()方法进行初始化.

        mInputChannel = inputChannel;        mMessageQueue = looper.getQueue();        mReceiverPtr = nativeInit(new WeakReference(this),                inputChannel, mMessageQueue);

在JNI层,首先获得了inputChannel和messageQueue的指针,并构造一个NativeInputEventReceiver对象.

352    sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,353            inputChannelObj);359    sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);365    sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,366            receiverWeak, inputChannel, messageQueue);

之后会调用receiver的initialize()方法.

122status_t NativeInputEventReceiver::initialize() {123    setFdEvents(ALOOPER_EVENT_INPUT);124    return OK;125}

setFdEvents函数中,会将client端的inputChannel的socket文件描述符加入到Looper的监控中.

162void NativeInputEventReceiver::setFdEvents(int events) {163    if (mFdEvents != events) {164        mFdEvents = events;165        int fd = mInputConsumer.getChannel()->getFd();166        if (events) {167            mMessageQueue->getLooper()->addFd(fd, 0, events, this, NULL);168        } else {169            mMessageQueue->getLooper()->removeFd(fd);170        }171    }172}173

InitInputChannel.jpg

当有消息到来的时候,会调用inputChannel对应的NativeInputEventReceiver回调函数.
它的handleEvent()函数中会调用consumeEvents函数,

        status_t status = consumeEvents(env, false /*consumeBatches*/, -1, NULL);

在 consumeEvents()函数中会调用到InputChannel的receiveMessage方法.

493            // Receive a fresh message.494            status_t result = mChannel->receiveMessage(&mMsg);

然后通过JNI调用到java层InputEventReceiver的dispatchInputEvent()回调函数.

330 env->CallVoidMethod(receiverObj.get(),331 gInputEventReceiverClassInfo.dispatchInputEvent, seq, inputEventObj);

    private void dispatchInputEvent(int seq, InputEvent event) {        mSeqMap.put(event.getSequenceNumber(), seq);        onInputEvent(event);    }

然后调用到ViewRoot的OnInputEvent()方法,继而调用了enqueuInputEvent()方法,

        if (processImmediately) {            doProcessInputEvents();        } else {            scheduleProcessInputEvents();        }

之后进入到delieverInputEvent()方法中,对stage进行判断,如果为空则结束分发,否则

        if (stage != null) {            stage.deliver(q);        } else {            finishInputEvent(q);        }

deliver()函数中会执行stage的onPorcess()方法.

              apply(q, onProcess(q));

这里的stage时这样取值的

        if (q.shouldSendToSynthesizer()) {            stage = mSyntheticInputStage;        } else {            stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;        }

这里InputStage的设计用到了流水线或者叫

责任链的模式

InputStage结构.jpg

InputStage有很多子类,所有InputStage类的构造方法都会传入一个InputStage类的变量,这样最终会形成流水线线式的处理结构,每经过一个InputStage对象的处理都会进行判断,看是否还需要将 events继续向前传输,如果需要就调用forward()函数让该变量中存储的下一个InputStage对象处理该events,如果不需要就调用finish()函数结束events的传输.
只需知道最终会调用到ViewRootImpl的enqueueInputEvent()方法.
该方法中会立即或者延迟处理events.

        if (processImmediately) {            doProcessInputEvents();        } else {            scheduleProcessInputEvents();        }

在　doProcessInputEvent()方法中会判断是否要经过IME输入法框架处理.

stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;

最后经过判断后会层层处理,最终进入到view.dispatchKeyEvent()方法中.

四.

最后返回到dispatchOnceLocked()函数中,执行runCommandsLockedInterruptible()函数.

323        // Run all pending commands if there are any.324        // If any commands were run then force the next poll to wake up immediately.325        if (runCommandsLockedInterruptible()) {326            nextWakeupTime = LONG_LONG_MIN;327        }

五.Epoll机制

epoll.jpg

Looper->wake()函数利用了linux中的epoll机制。
首先,注册一个epoll的实例描述符,将所有的管道对象的fd都注册到该epoll实例上,利用epoll_wait函数来睡眠等待管道上IO事件的发生;
调用PollOnce()函数来启动epoll_wait的睡眠等待,而wake()函数则是向epoll中的管道写入一个字符来唤醒epoll_wait.

六.InputChannel分析

InputChannel结构.jpeg

首先是server端的inputChannel注册
首先打开一对InputChannelPair，调用到JNI中的
android_view_InputChannel_nativeOpenInputChannelPair方法,最终会调用到linux中的socketPair()函数打开一对socket管道,而inputChannel就是由socket管道来构建的.

184 outServerChannel = **new** InputChannel(serverChannelName, sockets[0]);

inputChannel在WMS中注册,保存在一个WindowState的类中,WMS使用这对inputChannel的第一个
然后会调用registerInputChannel方法进行注册.

mInputManager.registerInputChannel(win.mInputChannel, win.mInputWindowHandle);

最终会调用Native层的方法

nativeRegisterInputChannel(mPtr, inputChannel, inputWindowHandle, false);

将inputChannel和connection保存在映射表中,mLooper加入对该fd的监听,当有数据到来的时候会唤醒等待的线程.

3511        sp connection = new Connection(inputChannel, inputWindowHandle, monitor);35123513        int fd = inputChannel->getFd();3514        mConnectionsByFd.add(fd, connection);3516        if (monitor) {3517            mMonitoringChannels.push(inputChannel);3518        }35193520        mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);

而当InputDispatcher分发消息时,会调用InputChannel::sendMessage()方法,该方法调用了linux socket中的send函数,向socket管道中写入数据.

client端inputChannel的注册

WMS中创建的inputChannel跨进程传输到cilent端,转换为client端的inputChannel使用.

讲解java JNI的注册:http://my.oschina.net/u/157503/blog