参考文章：http://blog.csdn.net/windskier/article/details/6966264
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总的来说是：
1.InputReader从EventHub读事件，写到InputDispatcher的队列中。
2.InputDispatcher从队列中读事件，分发给ViewRoot。
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具体一点是：
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1.文件InputDispatcher.cpp (frameworks\base\services\input)?190644?2011/12/12
?InputDispatcher有个内部类叫做 Connection。有两个重要属性：
一个是InputChannel，负责维护发送事件到ViewRoot的通道。
一个是InputPublisher，负责通知ViewRoot。
InputChannel维护了一个共享内存和一对管道。用来连接InputPublisher和InputConsummer
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2.文件 android_view_InputQueue.cpp (frameworks\base\core\jni)?19672?2011/12/12
的类??NativeInputQueue 也有两个重要的属性：
??????? sp<InputChannel> inputChannel;
??????? InputConsumer inputConsumer;
这两个属性与1InputDispatcher的两个属性一一对应。这样就在NativeInputQueue? 和 InputDispatcher之间 通过管道和共享内存，建立了一个进程间通信机制。负责事件的传输。
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经过研究发现，InputDispatcher一次就发布一个事件给所有的target。然后就等待应答信号。所有信号应答完毕后，清空InputChannel。在下一轮的dispatchOnce中，找到当前的焦点窗口，构造InpuChannel，并注册：
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void InputDispatcher::addWindowTargetLocked(const sp<InputWindowHandle>& windowHandle, int32_t targetFlags, BitSet32 pointerIds) { mCurrentInputTargets.push(); const InputWindowInfo* windowInfo = windowHandle->getInfo(); InputTarget& target = mCurrentInputTargets.editTop(); target.inputChannel = windowInfo->inputChannel; target.flags = targetFlags; target.xOffset = - windowInfo->frameLeft; target.yOffset = - windowInfo->frameTop; target.scaleFactor = windowInfo->scaleFactor; target.pointerIds = pointerIds;}3.Dispatcher有个超时机制：
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enum DropReason { DROP_REASON_NOT_DROPPED = 0, DROP_REASON_POLICY = 1, DROP_REASON_APP_SWITCH = 2, DROP_REASON_DISABLED = 3, DROP_REASON_BLOCKED = 4, DROP_REASON_STALE = 5, };?其中DROP_REASON_STALE 的超时是10秒。如果超过了10秒，事件没有处理掉，那么就直接丢弃。
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// Default input dispatching timeout if there is no focused application or paused window// from which to determine an appropriate dispatching timeout.const nsecs_t DEFAULT_INPUT_DISPATCHING_TIMEOUT = 5000 * 1000000LL; // 5 sec// Amount of time to allow for all pending events to be processed when an app switch// key is on the way. This is used to preempt input dispatch and drop input events// when an application takes too long to respond and the user has pressed an app switch key.const nsecs_t APP_SWITCH_TIMEOUT = 500 * 1000000LL; // 0.5sec// Amount of time to allow for an event to be dispatched (measured since its eventTime)// before considering it stale and dropping it.const nsecs_t STALE_EVENT_TIMEOUT = 10000 * 1000000LL; // 10sec// Motion samples that are received within this amount of time are simply coalesced// when batched instead of being appended. This is done because some drivers update// the location of pointers one at a time instead of all at once.// For example, when there are 10 fingers down, the input dispatcher may receive 10// samples in quick succession with only one finger's location changed in each sample.//// This value effectively imposes an upper bound on the touch sampling rate.// Touch sensors typically have a 50Hz - 200Hz sampling rate, so we expect distinct// samples to become available 5-20ms apart but individual finger reports can trickle// in over a period of 2-4ms or so.//// Empirical testing shows that a 2ms coalescing interval (500Hz) is not enough,// a 3ms coalescing interval (333Hz) works well most of the time and doesn't introduce// significant quantization noise on current hardware.const nsecs_t MOTION_SAMPLE_COALESCE_INTERVAL = 3 * 1000000LL; // 3ms, 333Hz
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