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;}open_device(devname) { open(...)  ioctl(...)}

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 jbooleanandroid_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();

InputDispatcherThread的实现代码如下：

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)            {                ... ...            }        }    }

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