Android Input子系统核心服务

基于Android 7.0源码分析

核心服务的类图

• InputManagerService
  • 负责管理Android输入子系统
  • 封装C++层的InputManager并提供回调
• NativeInputManager
  • InputManagerService的JNI实现
  • InputManagerService与C++层的InputManager之间的桥梁
• InputManager
  • Android系统输入事件处理的核心
• InputReader
  • 包含一些列InputMapper
• InputReaderThread
  • "InputReader"线程负责读取、预处理原始输入事件以及发送事件到由"InputDispatcherThread"线程管理队列中
• InputDispatcher
• InputDispatcherThread
  • "InputDispatcher"线程负责将新的事件异步的发送给应用
• EventHub
  • 从系统的输入设备获取事件，管理输入设备

核心服务的创建

下面从InputManagerService的创建开始分析

    ......
    // 添加Systrace以及system log
    traceBeginAndSlog("StartInputManagerService");
    // context为systemserver的上下文
    inputManager = new InputManagerService(context);
    Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
    ......

下面看InputManagerService的构造函数

    public InputManagerService(Context context) {
        this.mContext = context;
        // 创建InputManagerHandler用于与"android.display"线程通信
        this.mHandler = new InputManagerHandler(DisplayThread.get().getLooper());

        mUseDevInputEventForAudioJack =
                context.getResources().getBoolean(R.bool.config_useDevInputEventForAudioJack);
        Slog.i(TAG, "Initializing input manager, mUseDevInputEventForAudioJack="
                + mUseDevInputEventForAudioJack);
        // 创建NativeInputManager
        mPtr = nativeInit(this, mContext, mHandler.getLooper().getQueue());

        // 添加LocalService到LocalServices，用于SystemServer内部通信
        LocalServices.addService(InputManagerInternal.class, new LocalService());
    }

下面看nativeInit

static jlong nativeInit(JNIEnv* env, jclass /* clazz */,
        jobject serviceObj, jobject contextObj, jobject messageQueueObj) {
    // 这里messageQueue为"android.display"线程的消息队列
    sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
    if (messageQueue == NULL) {
        jniThrowRuntimeException(env, "MessageQueue is not initialized.");
        return 0;
    }

    // 创建NativeInputManager
    NativeInputManager* im = new NativeInputManager(contextObj, serviceObj,
            messageQueue->getLooper());
    im->incStrong(0);
    return reinterpret_cast<jlong>(im);
}

下面看NativeInputManager的创建

NativeInputManager::NativeInputManager(jobject contextObj,
        jobject serviceObj, const sp<Looper>& looper) :
        mLooper(looper), mInteractive(true) {
    JNIEnv* env = jniEnv();

    mContextObj = env->NewGlobalRef(contextObj);
    mServiceObj = env->NewGlobalRef(serviceObj);

    {
        AutoMutex _l(mLock);
        mLocked.systemUiVisibility = ASYSTEM_UI_VISIBILITY_STATUS_BAR_VISIBLE;
        mLocked.pointerSpeed = 0;
        mLocked.pointerGesturesEnabled = true;
        mLocked.showTouches = false;
    }
    mInteractive = true;

    // 创建EventHub
    sp<EventHub> eventHub = new EventHub();
    // 创建InputManager
    mInputManager = new InputManager(eventHub, this, this);
}

首先看EventHub的构造函数，然后看InputManager的创建

EventHub::EventHub(void) :
        mBuiltInKeyboardId(NO_BUILT_IN_KEYBOARD), mNextDeviceId(1), mControllerNumbers(),
        mOpeningDevices(0), mClosingDevices(0),
        mNeedToSendFinishedDeviceScan(false),
        mNeedToReopenDevices(false), mNeedToScanDevices(true),
        mPendingEventCount(0), mPendingEventIndex(0), mPendingINotify(false) {
    acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);
    // 创建epoll监听文件描述符
    mEpollFd = epoll_create(EPOLL_SIZE_HINT);
    LOG_ALWAYS_FATAL_IF(mEpollFd < 0, "Could not create epoll instance.  errno=%d", errno);

    // 创建通知事件队列
    mINotifyFd = inotify_init();
    // 创建观察者监视DEVICE_PATH(/dev/input)下的设备文件的创建与删除
    int result = inotify_add_watch(mINotifyFd, DEVICE_PATH, IN_DELETE | IN_CREATE);
    LOG_ALWAYS_FATAL_IF(result < 0, "Could not register INotify for %s.  errno=%d",
            DEVICE_PATH, errno);

    struct epoll_event eventItem;
    memset(&eventItem, 0, sizeof(eventItem));
    eventItem.events = EPOLLIN;
    eventItem.data.u32 = EPOLL_ID_INOTIFY;
    // 监听mINotifyFd
    result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mINotifyFd, &eventItem);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not add INotify to epoll instance.  errno=%d", errno);

    int wakeFds[2];
    // 创建pipe用于主动唤醒EventHub
    result = pipe(wakeFds);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not create wake pipe.  errno=%d", errno);

    mWakeReadPipeFd = wakeFds[0];
    mWakeWritePipeFd = wakeFds[1];

    result = fcntl(mWakeReadPipeFd, F_SETFL, O_NONBLOCK);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake read pipe non-blocking.  errno=%d",
            errno);

    result = fcntl(mWakeWritePipeFd, F_SETFL, O_NONBLOCK);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not make wake write pipe non-blocking.  errno=%d",
            errno);

    eventItem.data.u32 = EPOLL_ID_WAKE;
    // 监听mWakeReadPipeFd
    result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeReadPipeFd, &eventItem);
    LOG_ALWAYS_FATAL_IF(result != 0, "Could not add wake read pipe to epoll instance.  errno=%d",
            errno);

    int major, minor;
    getLinuxRelease(&major, &minor);
    // EPOLLWAKEUP was introduced in kernel 3.5
    mUsingEpollWakeup = major > 3 || (major == 3 && minor >= 5);
}

至此，EventHub还没有监听特定的输入设备文件描述符。下面看InputManager的创建

InputManager::InputManager(
        const sp<EventHubInterface>& eventHub,
        const sp<InputReaderPolicyInterface>& readerPolicy,
        const sp<InputDispatcherPolicyInterface>& dispatcherPolicy) {
    // 创建InputDispatcher，dispatcherPolicy引用NativeInputManager
    mDispatcher = new InputDispatcher(dispatcherPolicy);
    // 创建InputReader, readerPolicy引用NativeInputManager
    mReader = new InputReader(eventHub, readerPolicy, mDispatcher);
    // 创建InputDispatcherThread以及InputReaderThread
    initialize();
}

小结

• 策略模式

• 代理模式

核心服务的启动

下面从InputManagerService的start()开始分析

    ......
    // wm.getInputMonitor()返回InputMonitor对象
    inputManager.setWindowManagerCallbacks(wm.getInputMonitor());
    // 调用InputManagerService的start方法
    inputManager.start();
    ......

    public void start() {
        Slog.i(TAG, "Starting input manager");
        // 调用nativeStart，mPtr为NativeInputManager对象的地址
        nativeStart(mPtr);

        // Add ourself to the Watchdog monitors.
        Watchdog.getInstance().addMonitor(this);

        // 监听Setting数据库的改变
        registerPointerSpeedSettingObserver();
        registerShowTouchesSettingObserver();
        registerAccessibilityLargePointerSettingObserver();
        // 注册广播接收机，接收用户切换广播
        mContext.registerReceiver(new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                updatePointerSpeedFromSettings();
                updateShowTouchesFromSettings();
                updateAccessibilityLargePointerFromSettings();
            }
        }, new IntentFilter(Intent.ACTION_USER_SWITCHED), null, mHandler);
        // 获取Setting数据库信息
        updatePointerSpeedFromSettings();
        updateShowTouchesFromSettings();
        updateAccessibilityLargePointerFromSettings();
    }

下面看NativeStart()的实现

static void nativeStart(JNIEnv* env, jclass /* clazz */, jlong ptr) {
    NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);

    // 调用InputManager的start方法
    status_t result = im->getInputManager()->start();
    if (result) {
        jniThrowRuntimeException(env, "Input manager could not be started.");
    }
}

下面看InputManager的start()实现

status_t InputManager::start() {
    // 启动InputDispatcher线程
    status_t result = mDispatcherThread->run("InputDispatcher", PRIORITY_URGENT_DISPLAY);
    if (result) {
        ALOGE("Could not start InputDispatcher thread due to error %d.", result);
        return result;
    }
    // 启动InputReader线程
    result = mReaderThread->run("InputReader", PRIORITY_URGENT_DISPLAY);
    if (result) {
        ALOGE("Could not start InputReader thread due to error %d.", result);

        mDispatcherThread->requestExit();
        return result;
    }

    return OK;
}

至此，EventHub还不能接收输入事件，当InputReader线程启动后会请求EventHub扫描、添加输入设备,下面分析InputReader启动后，EventHub扫描、添加输入设备的过程。
我们从InputReaderThread的threadLoop()开始分析。

bool InputReaderThread::threadLoop() {
    // 调用InputReader的loopOnce()
    mReader->loopOnce();
    // 返回值为true,循环调用
    return true;
}

下面看InputReader的loopOnce()实现

void InputReader::loopOnce() {
    int32_t oldGeneration;
    int32_t timeoutMillis;
    bool inputDevicesChanged = false;
    ......
    // 读取输入事件，返回读取的事件数
    size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE);
    { // acquire lock
        AutoMutex _l(mLock);
        mReaderIsAliveCondition.broadcast();

        if (count) {
            // 处理输入事件
            processEventsLocked(mEventBuffer, count);
        }
        ......
    }
    ......
    // 通知InputDispatcherThread分发事件
    mQueuedListener->flush();
}

下面首先分析EventHub的getEvents()方法，然后看InputReader的processEventsLocked方法。

size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) {
    ALOG_ASSERT(bufferSize >= 1);

    AutoMutex _l(mLock);

    struct input_event readBuffer[bufferSize];

    RawEvent* event = buffer;
    size_t capacity = bufferSize;
    bool awoken = false;
    for (;;) {
        ......
        // 首次进入mNeedToScanDevices为true，扫描设备
        if (mNeedToScanDevices) {
            mNeedToScanDevices = false;
            scanDevicesLocked();
            mNeedToSendFinishedDeviceScan = true;
        }
        // 构造设备添加事件，mOpeningDevices指向设备链表头
        while (mOpeningDevices != NULL) {
            Device* device = mOpeningDevices;
            ALOGV("Reporting device opened: id=%d, name=%s\n",
                 device->id, device->path.string());
            mOpeningDevices = device->next;
            event->when = now;
            event->deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;
            event->type = DEVICE_ADDED;
            event += 1;
            mNeedToSendFinishedDeviceScan = true;
            if (--capacity == 0) {
                break;
            }
        }
        // 添加设备扫描完成事件
        if (mNeedToSendFinishedDeviceScan) {
            mNeedToSendFinishedDeviceScan = false;
            event->when = now;
            event->type = FINISHED_DEVICE_SCAN;
            event += 1;
            if (--capacity == 0) {
                break;
            }
        }
        ......
        // 有事件立即返回
        if (event != buffer || awoken) {
            break;
        }
        ......
    }

    // All done, return the number of events we read.
    return event - buffer;
}

下面看scanDevicesLocked()的实现

void EventHub::scanDevicesLocked() {
    // 扫描/dev/input下的输入设备
    status_t res = scanDirLocked(DEVICE_PATH);
    if(res < 0) {
        ALOGE("scan dir failed for %s\n", DEVICE_PATH);
    }
    // 创建虚拟按键设备
    if (mDevices.indexOfKey(VIRTUAL_KEYBOARD_ID) < 0) {
        createVirtualKeyboardLocked();
    }
}

下面看scanDirLocked()的实现

status_t EventHub::scanDirLocked(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);
        openDeviceLocked(devname);
    }
    closedir(dir);
    return 0;
}

scanDirLocked()的实现相对简单，扫描/dev/input目录下的设备文件，并打开合法的文件。下面看openDeviceLocked()的实现。

status_t EventHub::openDeviceLocked(const char *devicePath) {
    char buffer[80];

    ALOGV("Opening device: %s", devicePath);
    // 打开设备
    int fd = open(devicePath, O_RDWR | O_CLOEXEC);
    ......
    // Get device name.
    // 获取设备名
    if(ioctl(fd, EVIOCGNAME(sizeof(buffer) - 1), &buffer) < 1) {
        //fprintf(stderr, "could not get device name for %s, %s\n", devicePath, strerror(errno));
    } else {
        buffer[sizeof(buffer) - 1] = '\0';
        identifier.name.setTo(buffer);
    }
    ......
    // Check to see if the device is on our excluded list
    // 检查设备是否在排除列表中
    for (size_t i = 0; i < mExcludedDevices.size(); i++) {
        const String8& item = mExcludedDevices.itemAt(i);
        if (identifier.name == item) {
            ALOGI("ignoring event id %s driver %s\n", devicePath, item.string());
            close(fd);
            return -1;
        }
    }
    ......
    // 创建设备对象分配设备id
    // Allocate device.  (The device object takes ownership of the fd at this point.)
    int32_t deviceId = mNextDeviceId++;
    Device* device = new Device(fd, deviceId, String8(devicePath), identifier);
    ......
    // Load the configuration file for the device.
    // 加载设备配置文件(*.idc)
    loadConfigurationLocked(device);
    // Figure out the kinds of events the device reports.
    // 设置输入设备驱动上报的事件类型
    // EV_KEY 按键事件，EV_ABS 绝对坐标，如Touch事件
    ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(device->keyBitmask)), device->keyBitmask);
    ioctl(fd, EVIOCGBIT(EV_ABS, sizeof(device->absBitmask)), device->absBitmask);
    ioctl(fd, EVIOCGBIT(EV_REL, sizeof(device->relBitmask)), device->relBitmask);
    ioctl(fd, EVIOCGBIT(EV_SW, sizeof(device->swBitmask)), device->swBitmask);
    ioctl(fd, EVIOCGBIT(EV_LED, sizeof(device->ledBitmask)), device->ledBitmask);
    ioctl(fd, EVIOCGBIT(EV_FF, sizeof(device->ffBitmask)), device->ffBitmask);
    ioctl(fd, EVIOCGPROP(sizeof(device->propBitmask)), device->propBitmask);
    ......
    // Register with epoll.
    struct epoll_event eventItem;
    memset(&eventItem, 0, sizeof(eventItem));
    eventItem.events = EPOLLIN;
    if (mUsingEpollWakeup) {
        eventItem.events |= EPOLLWAKEUP;
    }
    eventItem.data.u32 = deviceId;
    // 设备文件描述符添加到EventHub的epoll
    if (epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, &eventItem)) {
        ALOGE("Could not add device fd to epoll instance.  errno=%d", errno);
        delete device;
        return -1;
    }
    ......
    // 设备添加到EventHub的mDevices中
    addDeviceLocked(device);
    return 0;
}

EventHub扫描完输入设备后，产生一系列设备添加事件，下面看InputReader处理设备添加事件。回到InputReader的loopOnce()中看processEventsLocked的实现。

void InputReader::processEventsLocked(const RawEvent* rawEvents, size_t count) {
    for (const RawEvent* rawEvent = rawEvents; count;) {
        int32_t type = rawEvent->type;
        size_t batchSize = 1;
        // 普通的输入事件，同一设备的事件作为一个batch
        if (type < EventHubInterface::FIRST_SYNTHETIC_EVENT) {
            int32_t deviceId = rawEvent->deviceId;
            while (batchSize < count) {
                if (rawEvent[batchSize].type >= EventHubInterface::FIRST_SYNTHETIC_EVENT
                        || rawEvent[batchSize].deviceId != deviceId) {
                    break;
                }
                batchSize += 1;
            }
#if DEBUG_RAW_EVENTS
            ALOGD("BatchSize: %d Count: %d", batchSize, count);
#endif
            processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
        } else {
            switch (rawEvent->type) {
            case EventHubInterface::DEVICE_ADDED:
                // 处理设备添加
                addDeviceLocked(rawEvent->when, rawEvent->deviceId);
                break;
            case EventHubInterface::DEVICE_REMOVED:
                removeDeviceLocked(rawEvent->when, rawEvent->deviceId);
                break;
            case EventHubInterface::FINISHED_DEVICE_SCAN:
                // 处理设备扫描完成
                handleConfigurationChangedLocked(rawEvent->when);
                break;
            default:
                ALOG_ASSERT(false); // can't happen
                break;
            }
        }
        count -= batchSize;
        rawEvent += batchSize;
    }
}

下面重点看设备添加事件处理函数addDeviceLocked()的实现

void InputReader::addDeviceLocked(nsecs_t when, int32_t deviceId) {
    ssize_t deviceIndex = mDevices.indexOfKey(deviceId);
    if (deviceIndex >= 0) {
        ALOGW("Ignoring spurious device added event for deviceId %d.", deviceId);
        return;
    }
    // 从EventHub获取设备信息
    InputDeviceIdentifier identifier = mEventHub->getDeviceIdentifier(deviceId);
    uint32_t classes = mEventHub->getDeviceClasses(deviceId);
    int32_t controllerNumber = mEventHub->getDeviceControllerNumber(deviceId);

    // 创建输入设备并添加相应的InputMapper
    InputDevice* device = createDeviceLocked(deviceId, controllerNumber, identifier, classes);
    device->configure(when, &mConfig, 0);
    device->reset(when);

    if (device->isIgnored()) {
        ALOGI("Device added: id=%d, name='%s' (ignored non-input device)", deviceId,
                identifier.name.string());
    } else {
        ALOGI("Device added: id=%d, name='%s', sources=0x%08x", deviceId,
                identifier.name.string(), device->getSources());
    }
    // 添加到mDevices中
    mDevices.add(deviceId, device);
    bumpGenerationLocked();
    ......
}

下面看createDeviceLocked()的实现

InputDevice* InputReader::createDeviceLocked(int32_t deviceId, int32_t controllerNumber,
        const InputDeviceIdentifier& identifier, uint32_t classes) {
    // 创建InputDevice
    InputDevice* device = new InputDevice(&mContext, deviceId, bumpGenerationLocked(),
            controllerNumber, identifier, classes);
    ......
    // Keyboard-like devices.
    // 类键盘设备添加InputMapper
    uint32_t keyboardSource = 0;
    // 普通的按键类型
    int32_t keyboardType = AINPUT_KEYBOARD_TYPE_NON_ALPHABETIC;
    if (classes & INPUT_DEVICE_CLASS_KEYBOARD) {
        // 普通的按键keyboardSource
        keyboardSource |= AINPUT_SOURCE_KEYBOARD;
    }
    if (classes & INPUT_DEVICE_CLASS_ALPHAKEY) {
        keyboardType = AINPUT_KEYBOARD_TYPE_ALPHABETIC;
    }
    if (classes & INPUT_DEVICE_CLASS_DPAD) {
        keyboardSource |= AINPUT_SOURCE_DPAD;
    }
    if (classes & INPUT_DEVICE_CLASS_GAMEPAD) {
        keyboardSource |= AINPUT_SOURCE_GAMEPAD;
    }

    if (keyboardSource != 0) {
        device->addMapper(new KeyboardInputMapper(device, keyboardSource, keyboardType));
    }

    // Cursor-like devices.
    // 类Cursor（鼠标或者traceball）设备添加InputMapper
    if (classes & INPUT_DEVICE_CLASS_CURSOR) {
        device->addMapper(new CursorInputMapper(device));
    }

    // Touchscreens and touchpad devices.
    // 触摸屏、触控板设备添加InputMapper
    if (classes & INPUT_DEVICE_CLASS_TOUCH_MT) {
        // 通常为MultiTouch
        device->addMapper(new MultiTouchInputMapper(device));
    } else if (classes & INPUT_DEVICE_CLASS_TOUCH) {
        device->addMapper(new SingleTouchInputMapper(device));
    }
    ......
}

InputMapper负责加工原始的输入事件，一个输入设备可以关联多个InputMapper，这样可以处理不同类型的事件。

至此，Input核心服务启动完成，接下来EventHub就可以监听驱动上报的输入事件了。