Android输入设备处理流程
原文地址::http://hi.baidu.com/viataa/blog/item/5a179f8fe349876f9e2fb4af.html
Android系统硬件的访问是通过HAL(Hardware Abstract Layer)来进行的，HAL就起到来Hardware adapter的作用。对于输入设备，如KeyPad、TouchPanel等，Android用EventHub具体的对其进行了封装。
输入设备驱动程序对用户空间应用程序提供一些设备文件，这些设备文件放在/dev/input里面。
1. EventHub扫描/dev/input下所有设备文件，并打开它们。
bool EventHub::openPlatformInput(void)
{
...
mFDCount = 1;
mFDs = (pollfd *)calloc(1, sizeof(mFDs[0]));
mDevices = (device_t **)calloc(1, sizeof(mDevices[0]));
mFDs[0].events = POLLIN;
mDevices[0] = NULL;
res = scan_dir(device_path);
...
return true;
}
int EventHub::scan_dir(const char *dirname)
{
char devname[PATH_MAX];
char *filename;
DIR *dir;
struct dirent *de;
dir = opendir(dirname);
if(dir == NULL)
return -1;
strcpy(devname, dirname);
filename = devname + strlen(devname);
*filename++ = '/';
while((de = readdir(dir)))
{
if(de->d_name[0] == '.' &&
(de->d_name[1] == '\0' ||
(de->d_name[1] == '.' && de->d_name[2] == '\0')))
continue;
strcpy(filename, de->d_name);
open_device(devname);
}
closedir(dir);
return 0;
}
}
EventHub对外提供了一个函数用于从输入设备文件中读取数据。
bool EventHub::getEvent(int32_t* outDeviceId, int32_t* outType,
int32_t* outScancode, int32_t* outKeycode, uint32_t *outFlags,
int32_t* outValue, nsecs_t* outWhen)
{
...
while(1)
{
// First, 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;
*outDeviceId = device->id;
if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0;
*outType = DEVICE_REMOVED;
delete device;
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;
*outDeviceId = device->id;
if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0;
*outType = DEVICE_ADDED;
return true;
}
release_wake_lock(WAKE_LOCK_ID);
pollres = poll(mFDs, mFDCount, -1);
acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);
if (pollres <= 0)
{
if (errno != EINTR)
{
LOGW("select failed (errno=%d)\n", errno);
usleep(100000);
}
continue;
}
for(i = 1; i < mFDCount; i++)
{
if(mFDs[i].revents)
{
LOGV("revents for %d = 0x%08x", i, mFDs[i].revents);
if(mFDs[i].revents & POLLIN)
{
res = read(mFDs[i].fd, &iev, sizeof(iev));
if (res == sizeof(iev))
{
LOGV("%s got: t0=%d, t1=%d, type=%d, code=%d, v=%d",
mDevices[i]->path.string(),
(int) iev.time.tv_sec, (int) iev.time.tv_usec,
iev.type, iev.code, iev.value);
*outDeviceId = mDevices[i]->id;
if (*outDeviceId == mFirstKeyboardId) *outDeviceId = 0;
*outType = iev.type;
*outScancode = iev.code;
if (iev.type == EV_KEY)
{
err = mDevices[i]->layoutMap->map(iev.code, outKeycode, outFlags);
LOGV("iev.code=%d outKeycode=%d outFlags=0x%08x err=%d\n",
iev.code, *outKeycode, *outFlags, err);
if (err != 0)
{
*outKeycode = 0;
*outFlags = 0;
}
}
else
{
*outKeycode = iev.code;
}
*outValue = iev.value;
*outWhen = s2ns(iev.time.tv_sec) + us2ns(iev.time.tv_usec);
return true;
}
else
{
if (res<0)
{
LOGW("could not get event (errno=%d)", errno);
}
else
{
LOGE("could not get event (wrong size: %d)", res);
}
continue;
}
}
}
}
...
}
对于按键事件，调用mDevices[i]->layoutMap->map进行映射。映射实际是由 KeyLayoutMap::map完成的，KeyLayoutMap类里读取配置文件qwerty.kl，由配置文件qwerty.kl决定键值的映射 关系。你可以通过修改./development/emulator/keymaps/qwerty.kl来改变键值的映射关系。
2. JNI函数
在frameworks/base/services/jni/com_android_server_KeyInputQueue.cpp文件 中，向JAVA提供了函数android_server_KeyInputQueue_readEvent，用于读取输入设备事件。
static jboolean
android_server_KeyInputQueue_readEvent(JNIEnv* env,
jobject clazz,
jobject event)
{
gLock.lock();
sp<EventHub> hub = gHub;
if (hub == NULL)
{
hub = new EventHub;
gHub = hub;
}
gLock.unlock();
int32_t deviceId;
int32_t type;
int32_t scancode, keycode;
uint32_t flags;
int32_t value;
nsecs_t when;
bool res = hub->getEvent(&deviceId, &type, &scancode, &keycode,
&flags, &value, &when);
env->SetIntField(event, gInputOffsets.mDeviceId, (jint)deviceId);
env->SetIntField(event, gInputOffsets.mType, (jint)type);
env->SetIntField(event, gInputOffsets.mScancode, (jint)scancode);
env->SetIntField(event, gInputOffsets.mKeycode, (jint)keycode);
env->SetIntField(event, gInputOffsets.mFlags, (jint)flags);
env->SetIntField(event, gInputOffsets.mValue, value);
env->SetLongField(event, gInputOffsets.mWhen,
(jlong)(nanoseconds_to_milliseconds(when)));
return res;
}
readEvent调用hub->getEvent读了取事件，然后转换成JAVA的结构。
3. 事件中转线程
在frameworks/base/services/java/com/android/server/KeyInputQueue.java里创建了一个线程，它循环的读取事件，然后把事件放入事件队列里。
Thread mThread = new Thread("InputDeviceReader")
{
public void run()
{
android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_URGENT_DISPLAY);
try
{
RawInputEvent ev = new RawInputEvent();
while (true)
{
InputDevice di;
readEvent(ev);
send = preprocessEvent(di, ev);
addLocked(di, curTime, ev.flags, ..., me);
}
}
}
};
注：readEvent就是调用了JNI的android_server_KeyInputQueue_readEven函数
4. 输入事件分发线程
在frameworks/base/services/java/com/android/server/WindowManagerService.java里创建了一个输入事件分发线程，它负责把事件分发到相应的窗口上去。
在WindowManagerService构造函数中调用
mInputThread = new InputDispatcherThread();
mInputThread.start();
private final class InputDispatcherThread extends Thread
{
// Time to wait when there is nothing to do: 9999 seconds.
static final int LONG_WAIT=9999*1000;
public InputDispatcherThread()
{
super("InputDispatcher");
}
@Override
public void run()
{
while (true) process();
}
private void process()
{
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_URGENT_DISPLAY);
... ...
while (true)
{
long curTime = SystemClock.uptimeMillis();
// Retrieve next event, waiting only as long as the next
// repeat timeout. If the configuration has changed, then
// don't wait at all -- we'll report the change as soon as
// we have processed all events.
QueuedEvent ev = mQueue.getEvent(
(int)((!configChanged && curTime < nextKeyTime)
? (nextKeyTime-curTime) : 0));
... ...
try
{
if (ev != null)
{
switch (ev.classType)
{
case RawInputEvent.CLASS_KEYBOARD:
...
dispatchKey((KeyEvent)ev.event, 0, 0);
mQueue.recycleEvent(ev);
break;
case RawInputEvent.CLASS_TOUCHSCREEN:
//Slog.i(TAG, "Read next event " + ev);
dispatchPointer(ev, (MotionEvent)ev.event, 0, 0);
break;
case RawInputEvent.CLASS_TRACKBALL:
dispatchTrackball(ev, (MotionEvent)ev.event, 0, 0);
break;
case RawInputEvent.CLASS_CONFIGURATION_CHANGED:
configChanged = true;
break;
default:
mQueue.recycleEvent(ev);
break;
}
} else if (configChanged)
{
configChanged = false;
sendNewConfiguration();
}
else if (lastKey != null)
{
curTime = SystemClock.uptimeMillis();
... ...
dispatchKey(newEvent, 0, 0);
}
else
{
curTime = SystemClock.uptimeMillis();
lastKeyTime = curTime;
nextKeyTime = curTime + LONG_WAIT;
}
}
catch (Exception e)
{
... ...
}
}
}