android Anr Input类型系统源码解析

我们常说Input超时，都是指的是Input事件分发超时，因此整个超时计算以及触发都在InputDispatcher这个类中。其代码路径如下：/frameworks/native/services/inputflinger/InputDispatcher.cpp，Input分发事件的时候就是不断执行InputDispatcher的threadLoop来读取Input事件，并调用dispatchOnce进行分发事件的。当然如果没有Input事件的时候，他会执行mLooper->pollOnce，进入等待状态。这个就和Android应用UI主线程的Looper一样，MessageQueue里面没有消息的时候，等待于nativePollOnce方法，其实最终还是调用Looper->pollOnce进入等待状态。

InputDispatcherThread dispatchOnce

// --- InputDispatcherThread ---InputDispatcherThread::InputDispatcherThread(const sp<InputDispatcherInterface>& dispatcher) :Thread(/*canCallJava*/ true), mDispatcher(dispatcher) {
}InputDispatcherThread::~InputDispatcherThread() {
}bool InputDispatcherThread::threadLoop() {mDispatcher->dispatchOnce();return true;
}} // namespace android

这个一个input 事件分发的线程。当收到一个消息的时候，会调用下面的DispatchOnce方法。

void InputDispatcher::dispatchOnce() {nsecs_t nextWakeupTime = LONG_LONG_MAX;{ // acquire lockAutoMutex _l(mLock);mDispatcherIsAliveCondition.broadcast();// Run a dispatch loop if there are no pending commands.// The dispatch loop might enqueue commands to run afterwards.if (!haveCommandsLocked()) {dispatchOnceInnerLocked(&nextWakeupTime);}// Run all pending commands if there are any.// If any commands were run then force the next poll to wake up immediately.if (runCommandsLockedInterruptible()) {nextWakeupTime = LONG_LONG_MIN;}} // release lock// Wait for callback or timeout or wake.  (make sure we round up, not down)nsecs_t currentTime = now();int timeoutMillis = toMillisecondTimeoutDelay(currentTime, nextWakeupTime);mLooper->pollOnce(timeoutMillis);
}

当一个input事件开始处理的时候，会在startDispatchCycleLocked 方法里面，给input 事件设置一个开始的时间。后面用来做超时判断使用。

void InputDispatcher::startDispatchCycleLocked(nsecs_t currentTime,const sp<Connection>& connection) {
#if DEBUG_DISPATCH_CYCLEALOGD("channel '%s' ~ startDispatchCycle",connection->getInputChannelName().c_str());
#endifwhile (connection->status == Connection::STATUS_NORMAL&& !connection->outboundQueue.isEmpty()) {DispatchEntry* dispatchEntry = connection->outboundQueue.head;dispatchEntry->deliveryTime = currentTime;

当一个事件，分发到InputDispatch.cpp，最终会调用到findFocusedWindowTargetsLocked 方法。
在里面，会先去调用checkWindowReadyForMoreInputLocked，检查一下当前的窗口是不是已经准备好可以处理新来的这个事件了。

int32_t InputDispatcher::findFocusedWindowTargetsLocked(nsecs_t currentTime,const EventEntry* entry, Vector<InputTarget>& inputTargets, nsecs_t* nextWakeupTime) {int32_t injectionResult;std::string reason;// Check whether the window is ready for more input.reason = checkWindowReadyForMoreInputLocked(currentTime,mFocusedWindowHandle, entry, "focused");if (!reason.empty()) {injectionResult = handleTargetsNotReadyLocked(currentTime, entry,mFocusedApplicationHandle, mFocusedWindowHandle, nextWakeupTime, reason.c_str());goto Unresponsive;}// Success!  Output targets.injectionResult = INPUT_EVENT_INJECTION_SUCCEEDED;addWindowTargetLocked(mFocusedWindowHandle,InputTarget::FLAG_FOREGROUND | InputTarget::FLAG_DISPATCH_AS_IS, BitSet32(0),inputTargets);// Done.
Failed:
Unresponsive:nsecs_t timeSpentWaitingForApplication = getTimeSpentWaitingForApplicationLocked(currentTime);updateDispatchStatisticsLocked(currentTime, entry,injectionResult, timeSpentWaitingForApplication);
#if DEBUG_FOCUSALOGD("findFocusedWindow finished: injectionResult=%d, ""timeSpentWaitingForApplication=%0.1fms",injectionResult, timeSpentWaitingForApplication / 1000000.0);
#endifreturn injectionResult;
}

checkWindowReadyForMoreInputLocked 检查是不是发生了anr:

std::string InputDispatcher::checkWindowReadyForMoreInputLocked(nsecs_t currentTime,const sp<InputWindowHandle>& windowHandle, const EventEntry* eventEntry,const char* targetType) {// If the window is paused then keep waiting.if (windowHandle->getInfo()->paused) {return StringPrintf("Waiting because the %s window is paused.", targetType);}// Touch events can always be sent to a window immediately because the user intended// to touch whatever was visible at the time.  Even if focus changes or a new// window appears moments later, the touch event was meant to be delivered to// whatever window happened to be on screen at the time.//// Generic motion events, such as trackball or joystick events are a little trickier.// Like key events, generic motion events are delivered to the focused window.// Unlike key events, generic motion events don't tend to transfer focus to other// windows and it is not important for them to be serialized.  So we prefer to deliver// generic motion events as soon as possible to improve efficiency and reduce lag// through batching.//// The one case where we pause input event delivery is when the wait queue is piling// up with lots of events because the application is not responding.// This condition ensures that ANRs are detected reliably.if (!connection->waitQueue.isEmpty()&& currentTime >= connection->waitQueue.head->deliveryTime+ STREAM_AHEAD_EVENT_TIMEOUT) {return StringPrintf("Waiting to send non-key event because the %s window has not ""finished processing certain input events that were delivered to it over ""%0.1fms ago.  Wait queue length: %d.  Wait queue head age: %0.1fms.",targetType, STREAM_AHEAD_EVENT_TIMEOUT * 0.000001f,connection->waitQueue.count(),(currentTime - connection->waitQueue.head->deliveryTime) * 0.000001f);}}return "";
}

这个方法是最关键的，他会去判断一下等待处理的事件队列是不是空的，如果不是空的，那么查看下队首的的消息处理事件是不是超时了，如果超时了，就会出发ANR.

总结：

Input 类型的ANR，如果你点击了屏幕，做了一个很耗时的操作，5s之后是不是弹出ANR弹窗的。只有当你再次点击屏幕的时候，才会触发。因为input 类型的ANR,他没有使用Handler.sendMessageDeley 这种方式去做处理。当点击了一个按钮，如果这个onClick 里面把线程睡眠了20s，只要你不再次点击屏幕，都不会触发ANR。只有在这个过程中，你再次点击屏幕，又走到了InputDispath.cpp 的DispatchOnce 里面，他会去检测，当前窗口的input 事件是不是处理完了，如果没有处理完，那么判断一下当前的时间和input消息队列里队首的input 事件，是否大于5s，如果大于5s，触发ANR 逻辑。

参考：
https://www.jianshu.com/p/1c827675f457
https://blog.csdn.net/abm1993/article/details/80461752
https://www.jianshu.com/p/914df9091a80
https://blog.csdn.net/abm1993/article/details/80461752