Activity取消注册InputChannel(十二)

1,概念

在启动一个acitivity时,将该activity和服务进程的InputChannel对应,这样事件就可以通过sockets进行通信了。

但是只有当前显示的acitivity才会获取事件,这就说明,在有一刻,会断开其他acitivity和服务进程的对应关系。

比如,销毁activity时就会断开该对应关系。

2,取消注册分析

销毁activity时会调用activity的finish方法,

private void finish(boolean finishTask) {if (mParent == null) {int resultCode;Intent resultData;synchronized (this) {resultCode = mResultCode;resultData = mResultData;}if (false) Log.v(TAG, "Finishing self: token=" + mToken);try {if (resultData != null) {resultData.prepareToLeaveProcess();}if (ActivityManagerNative.getDefault().finishActivity(mToken, resultCode, resultData, finishTask)) {mFinished = true;}} catch (RemoteException e) {// Empty}} else {mParent.finishFromChild(this);}}

直接调用ActivityManagerNative的finishActivity方法,然后跨进程调用ActivityManagerService的finishActivity方法,

AMS服务处理之后,然后又回调apk的ActivityThread进行处理, ActivityThread首先发送DESTROY_ACTIVITY消息切换到主线程,

调用handleDestroyActivity方法进一步处理。流程图如下,

从应用apk转到系统服务进程,然后又转回应用apk,

又从应用apk转到系统服务进程,终于出现了IMS服务,

C/C++层调用流程图如下,

转个来转个去,终于找到点子上了,

static void nativeUnregisterInputChannel(JNIEnv* env, jclass /* clazz */,jlong ptr, jobject inputChannelObj) {NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,inputChannelObj);if (inputChannel == NULL) {throwInputChannelNotInitialized(env);return;}android_view_InputChannel_setDisposeCallback(env, inputChannelObj, NULL, NULL);status_t status = im->unregisterInputChannel(env, inputChannel);if (status && status != BAD_VALUE) { // ignore already unregistered channelString8 message;message.appendFormat("Failed to unregister input channel.  status=%d", status);jniThrowRuntimeException(env, message.string());}

im是NativeInputManager对象,而NativeInputManager是com_android_server_input_InputManagerService.cpp中的一个内部类,

status_t NativeInputManager::unregisterInputChannel(JNIEnv* /* env */,const sp<InputChannel>& inputChannel) {return mInputManager->getDispatcher()->unregisterInputChannel(inputChannel);
}

得到的是InputDispatcher对象,调用其unregisterInputChannel方法,

status_t InputDispatcher::unregisterInputChannel(const sp<InputChannel>& inputChannel) {
#if DEBUG_REGISTRATIONALOGD("channel '%s' ~ unregisterInputChannel", inputChannel->getName().string());
#endif{ // acquire lockAutoMutex _l(mLock);status_t status = unregisterInputChannelLocked(inputChannel, false /*notify*/);if (status) {return status;}} // release lock// Wake the poll loop because removing the connection may have changed the current// synchronization state.mLooper->wake();return OK;
}

status_t InputDispatcher::unregisterInputChannelLocked(const sp<InputChannel>& inputChannel,bool notify) {ssize_t connectionIndex = getConnectionIndexLocked(inputChannel);if (connectionIndex < 0) {ALOGW("Attempted to unregister already unregistered input channel '%s'",inputChannel->getName().string());return BAD_VALUE;}sp<Connection> connection = mConnectionsByFd.valueAt(connectionIndex); // 找到索引mConnectionsByFd.removeItemsAt(connectionIndex); // 从mConnectionsByFd中删除if (connection->monitor) {removeMonitorChannelLocked(inputChannel);}mLooper->removeFd(inputChannel->getFd());//从Looper中删除nsecs_t currentTime = now();abortBrokenDispatchCycleLocked(currentTime, connection, notify);connection->status = Connection::STATUS_ZOMBIE;return OK;
}

这2个方法和注册(registerInputChannel)刚好相反,

Looper的removeFd方法如下,

int Looper::removeFd(int fd, int seq) {
#if DEBUG_CALLBACKSALOGD("%p ~ removeFd - fd=%d, seq=%d", this, fd, seq);
#endif{ // acquire lockAutoMutex _l(mLock);ssize_t requestIndex = mRequests.indexOfKey(fd);if (requestIndex < 0) {return 0;}// Check the sequence number if one was given.if (seq != -1 && mRequests.valueAt(requestIndex).seq != seq) {
#if DEBUG_CALLBACKSALOGD("%p ~ removeFd - sequence number mismatch, oldSeq=%d",this, mRequests.valueAt(requestIndex).seq);
#endifreturn 0;}// Always remove the FD from the request map even if an error occurs while// updating the epoll set so that we avoid accidentally leaking callbacks.mRequests.removeItemsAt(requestIndex); // 移除索引
•••

在Looper中,底层消息来时, pollInner方法会遍历mResponses数组,并将回调handleEvent方法,

for (size_t i = 0; i < mResponses.size(); i++) {Response& response = mResponses.editItemAt(i);if (response.request.ident == POLL_CALLBACK) {int fd = response.request.fd;int events = response.events;void* data = response.request.data;
#if DEBUG_POLL_AND_WAKE || DEBUG_CALLBACKSALOGD("%p ~ pollOnce - invoking fd event callback %p: fd=%d, events=0x%x, data=%p",this, response.request.callback.get(), fd, events, data);
#endif// Invoke the callback.  Note that the file descriptor may be closed by// the callback (and potentially even reused) before the function returns so// we need to be a little careful when removing the file descriptor afterwards.int callbackResult = response.request.callback->handleEvent(fd, events, data);if (callbackResult == 0) {removeFd(fd, response.request.seq);}// Clear the callback reference in the response structure promptly because we// will not clear the response vector itself until the next poll.response.request.callback.clear();result = POLL_CALLBACK;}}

由于在removeFd方法中已经去掉了被销毁(未显示)的activity的对应索引,所以仅有当前显示的activity才可以收到消息。