Step 18. EventHub.getEvent
这个函数定义在frameworks/base/libs/ui/EventHub.cpp文件中：
- bool EventHub::getEvent(RawEvent* outEvent)
- {
- outEvent->deviceId = 0;
- outEvent->type = 0;
- outEvent->scanCode = 0;
- outEvent->keyCode = 0;
- outEvent->flags = 0;
- outEvent->value = 0;
- outEvent->when = 0;
- // Note that we only allow one caller to getEvent(), so don't need
- // to do locking here... only when adding/removing devices.
- if (!mOpened) {
- mError = openPlatformInput() ? NO_ERROR : UNKNOWN_ERROR;
- mOpened = true;
- mNeedToSendFinishedDeviceScan = true;
- }
- for (;;) {
- // Report any devices that had last been added/removed.
- if (mClosingDevices != NULL) {
- device_t* device = mClosingDevices;
- LOGV("Reporting device closed: id=0x%x, name=%s\n",
- device->id, device->path.string());
- mClosingDevices = device->next;
- if (device->id == mFirstKeyboardId) {
- outEvent->deviceId = 0;
- } else {
- outEvent->deviceId = device->id;
- }
- outEvent->type = DEVICE_REMOVED;
- outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
- delete device;
- mNeedToSendFinishedDeviceScan = true;
- return true;
- }
- if (mOpeningDevices != NULL) {
- device_t* device = mOpeningDevices;
- LOGV("Reporting device opened: id=0x%x, name=%s\n",
- device->id, device->path.string());
- mOpeningDevices = device->next;
- if (device->id == mFirstKeyboardId) {
- outEvent->deviceId = 0;
- } else {
- outEvent->deviceId = device->id;
- }
- outEvent->type = DEVICE_ADDED;
- outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
- mNeedToSendFinishedDeviceScan = true;
- return true;
- }
- if (mNeedToSendFinishedDeviceScan) {
- mNeedToSendFinishedDeviceScan = false;
- outEvent->type = FINISHED_DEVICE_SCAN;
- outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
- return true;
- }
- // Grab the next input event.
- for (;;) {
- // Consume buffered input events, if any.
- if (mInputBufferIndex < mInputBufferCount) {
- const struct input_event& iev = mInputBufferData[mInputBufferIndex++];
- const device_t* device = mDevices[mInputDeviceIndex];
- LOGV("%s got: t0=%d, t1=%d, type=%d, code=%d, v=%d", device->path.string(),
- (int) iev.time.tv_sec, (int) iev.time.tv_usec, iev.type, iev.code, iev.value);
- if (device->id == mFirstKeyboardId) {
- outEvent->deviceId = 0;
- } else {
- outEvent->deviceId = device->id;
- }
- outEvent->type = iev.type;
- outEvent->scanCode = iev.code;
- if (iev.type == EV_KEY) {
- status_t err = device->layoutMap->map(iev.code,
- & outEvent->keyCode, & outEvent->flags);
- LOGV("iev.code=%d keyCode=%d flags=0x%08x err=%d\n",
- iev.code, outEvent->keyCode, outEvent->flags, err);
- if (err != 0) {
- outEvent->keyCode = AKEYCODE_UNKNOWN;
- outEvent->flags = 0;
- }
- } else {
- outEvent->keyCode = iev.code;
- }
- outEvent->value = iev.value;
- // Use an event timestamp in the same timebase as
- // java.lang.System.nanoTime() and android.os.SystemClock.uptimeMillis()
- // as expected by the rest of the system.
- outEvent->when = systemTime(SYSTEM_TIME_MONOTONIC);
- return true;
- }
- // Finish reading all events from devices identified in previous poll().
- // This code assumes that mInputDeviceIndex is initially 0 and that the
- // revents member of pollfd is initialized to 0 when the device is first added.
- // Since mFDs[0] is used for inotify, we process regular events starting at index 1.
- mInputDeviceIndex += 1;
- if (mInputDeviceIndex >= mFDCount) {
- break;
- }
- const struct pollfd& pfd = mFDs[mInputDeviceIndex];
- if (pfd.revents & POLLIN) {
- int32_t readSize = read(pfd.fd, mInputBufferData,
- sizeof(struct input_event) * INPUT_BUFFER_SIZE);
- if (readSize < 0) {
- if (errno != EAGAIN && errno != EINTR) {
- LOGW("could not get event (errno=%d)", errno);
- }
- } else if ((readSize % sizeof(struct input_event)) != 0) {
- LOGE("could not get event (wrong size: %d)", readSize);
- } else {
- mInputBufferCount = readSize / sizeof(struct input_event);
- mInputBufferIndex = 0;
- }
- }
- }
- ......
- mInputDeviceIndex = 0;
- // Poll for events. Mind the wake lock dance!
- // We hold a wake lock at all times except during poll(). This works due to some
- // subtle choreography. When a device driver has pending (unread) events, it acquires
- // a kernel wake lock. However, once the last pending event has been read, the device
- // driver will release the kernel wake lock. To prevent the system from going to sleep
- // when this happens, the EventHub holds onto its own user wake lock while the client
- // is processing events. Thus the system can only sleep if there are no events
- // pending or currently being processed.
- release_wake_lock(WAKE_LOCK_ID);
- int pollResult = poll(mFDs, mFDCount, -1);
- acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);
- if (pollResult <= 0) {
- if (errno != EINTR) {
- LOGW("poll failed (errno=%d)\n", errno);
- usleep(100000);
- }
- }
- }
- }
这个函数比较长，我们一步一步来分析。
首先，如果是第一次进入到这个函数中时，成员变量mOpened的值为false，于是就会调用openPlatformInput函数来打开系统输入设备，在本文中，我们主要讨论的输入设备就是键盘了。打开了这些输入设备文件后，就可以对这些输入设备进行是监控了。如果不是第一次进入到这个函数，那么就会分析当前有没有输入事件发生，如果有，就返回这个事件，否则就会进入等待状态，等待下一次输入事件的发生。在我们这个场景中，就是等待下一次键盘事件的发生了。
我们先分析openPlatformInput函数的实现，然后回过头来分析这个getEvent函数的具体的实现。
本文转自 Luoshengyang 51CTO博客，原文链接：http://blog.51cto.com/shyluo/966613，如需转载请自行联系原作者
