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Android输入输出机制之来龙去脉之前生后世

博客分类：

Android游戏框架

Android

密码太多记不了，怎么办？

http://a.app.qq.com/o/simple.jsp?pkgname=com.wa505.kf.epassword

补充一下更详细的解说图，在输入输出系统中存在很多类，这些类很难分清进程边界。

从图中可以看出，整个输入输出采用的是双队列缓冲。

其中的进程间通信采用的是共享内存+管道+信号量，整个通信过程没有涉及Binder。因为使用了android中的匿名共享内存，而共享内存不存在数据复制的问题，因此速度非常快。

先讲一下基本一般的输入处理方式的知识。一般的输入输出采用生产者，消费者模式，并构造队列进行处理，如下图

这种输入模型在android的系统中很多地方采用，先从最底层说起：

为了由于触屏事件频率很高，android设计者讲一个循环线程，拆分为两级循环，并做了个队列来进行缓冲。

InputDispatcherThread和InputReaderThread。InputDispatcherThread在自己的循环中对InputReaderThread请求同步，InputReaderThread收到同步信号后，把事件放入InputDispatcher的队列中。

具体代码如下：

InputReader.cpp中有很多InputMapper,有SwitchInputMapper，KeyBoardInputMapper，TrackballInputMapper，SingleTouchInputMapper，

MultiTouchInputMapper。当线程从EventHub读取到Event后，调用这些InputMapper的pocess方法：

文件InputReader.cpp中：

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


void InputReader::loopOnce() {
    RawEvent rawEvent;
    mEventHub->getEvent(& rawEvent);

#if DEBUG_RAW_EVENTS
    LOGD("Input event: device=0x%x type=0x%x scancode=%d keycode=%d value=%d",
            rawEvent.deviceId, rawEvent.type, rawEvent.scanCode, rawEvent.keyCode,
            rawEvent.value);
#endif

    process(& rawEvent);
}

process如下

void InputReader::process(const RawEvent* rawEvent) {
    switch (rawEvent->type) {
    default:
        consumeEvent(rawEvent);
        break;
    }
}

void InputReader::process(const RawEvent* rawEvent) {
    switch (rawEvent->type) {
        consumeEvent(rawEvent);
        break;
    }
}

consumeEvent(rawEvent);

方法是关键，下面继续跟进；

void InputReader::consumeEvent(const RawEvent* rawEvent) {
    int32_t deviceId = rawEvent->deviceId;

    { 
        device->process(rawEvent);
    } // release device registry reader lock
}

device->process(rawEvent)行，跟进去：

void InputDevice::process(const RawEvent* rawEvent) {
    size_t numMappers = mMappers.size();
    for (size_t i = 0; i < numMappers; i++) {
        InputMapper* mapper = mMappers[i];
        mapper->process(rawEvent);
    }
}

下面进入了IputMapper，InputMapper是个纯虚类，process是个纯虚方法，随便找个例子跟进去：

void SingleTouchInputMapper::process(const RawEvent* rawEvent) {
    switch (rawEvent->type) {
    case EV_KEY:
        switch (rawEvent->scanCode) {
        case BTN_TOUCH:
            mAccumulator.fields |= Accumulator::FIELD_BTN_TOUCH;
            mAccumulator.btnTouch = rawEvent->value != 0;
            // Don't sync immediately.  Wait until the next SYN_REPORT since we might
            // not have received valid position information yet.  This logic assumes that
            // BTN_TOUCH is always followed by SYN_REPORT as part of a complete packet.
            break;
        }
        break;
    case EV_SYN:
        switch (rawEvent->scanCode) {
        case SYN_REPORT:
            sync(rawEvent->when);
            break;
        }
        break;
    }
}

最关键的是

 sync(rawEvent->when);

展开如下：

void SingleTouchInputMapper::sync(nsecs_t when) {

    syncTouch(when, true);

 
}

void TouchInputMapper::syncTouch(nsecs_t when, bool havePointerIds) {
   
    if (touchResult == DISPATCH_TOUCH) {
        detectGestures(when);
        dispatchTouches(when, policyFlags);
    }
}

这两行，一个是虚拟键盘，一个是触摸屏。

TouchResult touchResult = consumeOffScreenTouches(when, policyFlags);

dispatchTouches

只说触摸屏，虚拟键类似，触摸屏调用的是

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

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

这个方法展开如下：

void TouchInputMapper::dispatchTouch(nsecs_t when, uint32_t policyFlags,
        TouchData* touch, BitSet32 idBits, uint32_t changedId, uint32_t pointerCount,
        int32_t motionEventAction) {
    int32_t pointerIds[MAX_POINTERS];
    PointerCoords pointerCoords[MAX_POINTERS];
    int32_t motionEventEdgeFlags = 0;
    float xPrecision, yPrecision;

    { 
    getDispatcher()->notifyMotion(when, getDeviceId(), getSources(), policyFlags,
            motionEventAction, 0, getContext()->getGlobalMetaState(), motionEventEdgeFlags,
            pointerCount, pointerIds, pointerCoords,
            xPrecision, yPrecision, mDownTime);
}

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

 void InputDispatcher::notifyMotion(nsecs_t eventTime, int32_t deviceId, int32_t source,
        uint32_t policyFlags, int32_t action, int32_t flags, int32_t metaState, int32_t edgeFlags,
        uint32_t pointerCount, const int32_t* pointerIds, const PointerCoords* pointerCoords,
        float xPrecision, float yPrecision, nsecs_t downTime) {      

 // Just enqueue a new motion event.
        MotionEntry* newEntry = mAllocator.obtainMotionEntry(eventTime,
                deviceId, source, policyFlags, action, flags, metaState, edgeFlags,
                xPrecision, yPrecision, downTime,
                pointerCount, pointerIds, pointerCoords);

        needWake = enqueueInboundEventLocked(newEntry);
}

最后一句：

 needWake = enqueueInboundEventLocked(newEntry);

bool InputDispatcher::enqueueInboundEventLocked(EventEntry* entry) {
    bool needWake = mInboundQueue.isEmpty();
    mInboundQueue.enqueueAtTail(entry);

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

    return needWake;
}

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

那么InputDispatcher又是如何从队列中取出来的呢？累了。

InputDiapather的

dispatchOnce

方法如下：

void InputDispatcher::dispatchOnce() {
    nsecs_t keyRepeatTimeout = mPolicy->getKeyRepeatTimeout();
    nsecs_t keyRepeatDelay = mPolicy->getKeyRepeatDelay();

    nsecs_t nextWakeupTime = LONG_LONG_MAX;
    { // acquire lock
        AutoMutex _l(mLock);
        dispatchOnceInnerLocked(keyRepeatTimeout, keyRepeatDelay, & nextWakeupTime);

        if (runCommandsLockedInterruptible()) {
            nextWakeupTime = LONG_LONG_MIN;  // force next poll to wake up immediately
        }
    } // release lock

    // Wait for callback or timeout or wake.  (make sure we round up, not down)
    nsecs_t currentTime = now();
    int32_t timeoutMillis;
    if (nextWakeupTime > currentTime) {
        uint64_t timeout = uint64_t(nextWakeupTime - currentTime);
        timeout = (timeout + 999999LL) / 1000000LL;
        timeoutMillis = timeout > INT_MAX ? -1 : int32_t(timeout);
    } else {
        timeoutMillis = 0;
    }

    mLooper->pollOnce(timeoutMillis);
}

最关键的是

  dispatchOnceInnerLocked(keyRepeatTimeout, keyRepeatDelay, & nextWakeupTime);

和

    mLooper->pollOnce(timeoutMillis);//这个是个回调。

代码又长又臭

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

}

dispatchMotionLocked

方法调用prepareDispatchCycleLocked，调用startDispatchCycleLocked，最终调用

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

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

    然后// Send the dispatch signal.
    status = connection->inputPublisher.sendDispatchSignal();
    if (status) {
        LOGE("channel '%s' ~ Could not send dispatch signal, status=%d",
                connection->getInputChannelName(), status);
        abortBrokenDispatchCycleLocked(currentTime, connection);
        return;
    }

至此，InputDisapatcher也结束了。

既然发布出去，必然有订阅者：在InputTransport.cpp中

status_t InputConsumer::consume(InputEventFactoryInterface* factory, InputEvent** outEvent) {
#if DEBUG_TRANSPORT_ACTIONS
    LOGD("channel '%s' consumer ~ consume",
            mChannel->getName().string());
#endif

    *outEvent = NULL;

    int ashmemFd = mChannel->getAshmemFd();
    int result = ashmem_pin_region(ashmemFd, 0, 0);
    if (result != ASHMEM_NOT_PURGED) {
        if (result == ASHMEM_WAS_PURGED) {
            LOGE("channel '%s' consumer ~ Error %d pinning ashmem fd %d because it was purged "
                    "which probably indicates that the publisher and consumer are out of sync.",
                    mChannel->getName().string(), result, ashmemFd);
            return INVALID_OPERATION;
        }

        LOGE("channel '%s' consumer ~ Error %d pinning ashmem fd %d.",
                mChannel->getName().string(), result, ashmemFd);
        return UNKNOWN_ERROR;
    }

    if (mSharedMessage->consumed) {
        LOGE("channel '%s' consumer ~ The current message has already been consumed.",
                mChannel->getName().string());
        return INVALID_OPERATION;
    }

    // Acquire but *never release* the semaphore.  Contention on the semaphore is used to signal
    // to the publisher that the message has been consumed (or is in the process of being
    // consumed).  Eventually the publisher will reinitialize the semaphore for the next message.
    result = sem_wait(& mSharedMessage->semaphore);
    if (result < 0) {
        LOGE("channel '%s' consumer ~ Error %d in sem_wait.",
                mChannel->getName().string(), errno);
        return UNKNOWN_ERROR;
    }

    mSharedMessage->consumed = true;

    switch (mSharedMessage->type) {
    case AINPUT_EVENT_TYPE_KEY: {
        KeyEvent* keyEvent = factory->createKeyEvent();
        if (! keyEvent) return NO_MEMORY;

        populateKeyEvent(keyEvent);

        *outEvent = keyEvent;
        break;
    }

    case AINPUT_EVENT_TYPE_MOTION: {
        MotionEvent* motionEvent = factory->createMotionEvent();
        if (! motionEvent) return NO_MEMORY;

        populateMotionEvent(motionEvent);

        *outEvent = motionEvent;
        break;
    }

    default:
        LOGE("channel '%s' consumer ~ Received message of unknown type %d",
                mChannel->getName().string(), mSharedMessage->type);
        return UNKNOWN_ERROR;
    }

    return OK;
}

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

聚焦到这里

status_t NativeInputQueue::registerInputChannel(JNIEnv* env, jobject inputChannelObj,
        jobject inputHandlerObj, jobject messageQueueObj) {
    sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
            inputChannelObj);
    if (inputChannel == NULL) {
        LOGW("Input channel is not initialized.");
        return BAD_VALUE;
    }

#if DEBUG_REGISTRATION
    LOGD("channel '%s' - Registered", inputChannel->getName().string());
#endif

    sp<Looper> looper = android_os_MessageQueue_getLooper(env, messageQueueObj);

    { // acquire lock
        AutoMutex _l(mLock);

        if (getConnectionIndex(inputChannel) >= 0) {
            LOGW("Attempted to register already registered input channel '%s'",
                    inputChannel->getName().string());
            return BAD_VALUE;
        }

        uint16_t connectionId = mNextConnectionId++;
        sp<Connection> connection = new Connection(connectionId, inputChannel, looper);
        status_t result = connection->inputConsumer.initialize();
        if (result) {
            LOGW("Failed to initialize input consumer for input channel '%s', status=%d",
                    inputChannel->getName().string(), result);
            return result;
        }

        connection->inputHandlerObjGlobal = env->NewGlobalRef(inputHandlerObj);

        int32_t receiveFd = inputChannel->getReceivePipeFd();
        mConnectionsByReceiveFd.add(receiveFd, connection);

        looper->addFd(receiveFd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);
    } // release lock

    android_view_InputChannel_setDisposeCallback(env, inputChannelObj,
            handleInputChannelDisposed, this);
    return OK;
}

也许更想知道的是消息队列在什么地方，进入InputQueue.java来看

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

在ViewRoot.java中有这么几行

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

完毕。

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

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

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

looper就是android中的【用户进程的循环】

注册的代码为：

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

回调的java函数为

    
回调的java代码的方法入口为：InputQueue.java中的。

@SuppressWarnings("unused")
    private static void dispatchMotionEvent(InputHandler inputHandler,
            MotionEvent event, long finishedToken) {
        Runnable finishedCallback = FinishedCallback.obtain(finishedToken);
        inputHandler.handleMotion(event, finishedCallback);
    }

这样就回调到了ViewRoot中