Android2.3平台输入输出机制之总结

xiaoxiao2021-02-28  77

参考文章:http://blog.csdn.net/windskier/article/details/6966264

 

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。

 

 

具体一点是:

 

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

 

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。

 

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:

 

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:

 

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。

 

 

// 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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