Android input子系统之InputReader获取输入事件详细分析--EventHub->getevents

此文章只分析EventHub获取输入事件的getevents函数的具体实现

首先在EventHub的构造函数中,将以下变量进行初始化,以下初始化变量在getevents中会用到


        mBuiltInKeyboardId(NO_BUILT_IN_KEYBOARD),  mNextDeviceId(1), mControllerNumbers(),

        mOpeningDevices(0), mClosingDevices(0),mNeedToSendFinishedDeviceScan(false),
        mNeedToReopenDevices(false), mNeedToScanDevices(true),

        mPendingEventCount(0), mPendingEventIndex(0), mPendingINotify(false)

下面来分析getevents:

size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize)

1.定义一个 input_event 结构的 readBuffer[buffersize] 来存储从 /dev/input/event*读取到的数据

2.定义一个 RawEvent的指针,指向 getEvents方法的参数 buffer指针中,返回给调用者InputReader对象的loopOnce方法

3.定义一个size_t capacity = bufferSize;

4.bool awoken = false;

5.进入到一个fo循环中

5.1 获取当前系统的时间,单位为ns 

    nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);

5.2  判断变量 mNeedToReopenDevices,来判断是否重新打开设备,mNeedToReopenDevices变量在EventHub的构造函数中初始化false,所以此条件并不成立,不需要重新ReopenDevices,关于mNeedToReopenDevices变量的调用过程详细分析参见

https://blog.csdn.net/qq_30025621/article/details/79944825

    if (mNeedToReopenDevices) {    

            mNeedToReopenDevices = false;

            ALOGI("Reopening all input devices due to a configuration change.");

            closeAllDevicesLocked();
            mNeedToScanDevices = true;

            break; // return to the caller before we actually rescan

    }

5.3 如果mClosingDevices存在,那么将用mClosingDevices中的每一个对象构造RawEvent对象,并将

    mNeedToSendFinishedDeviceScan设置为true,mClosingDevices详细分析参考如下:

    

    android input子系统--InputReader EventHub::getevents之mClosingDevices调用过程详细分析

        while (mClosingDevices) {
            Device* device = mClosingDevices;
            ALOGV("Reporting device closed: id=%d, name=%s\n",
                 device->id, device->path.string());
            mClosingDevices = device->next;
            event->when = now;
            event->deviceId = device->id == mBuiltInKeyboardId ? BUILT_IN_KEYBOARD_ID : device->id;
            event->type = DEVICE_REMOVED;
            event += 1;
            delete device;
            mNeedToSendFinishedDeviceScan = true;
            if (--capacity == 0) {
                break;
            }
        }

5.4 判断mNeedToScanDevices变量,确定是否需要进行设备的扫描(是否有设备发生变化),在系统开始初始化的时候,

    mNeedToScanDevices=true,所以此处成立,当mNeedToReopenDevices=true的时候,mNeedToScanDevices

    也为true,关于mNeedToScanDevices变量的详细分析,参考:

    android input子系统--InputReader EventHub::getevents之mNeedToScanDevices变量详细分析

        if (mNeedToScanDevices) {
            mNeedToScanDevices = false;
            scanDevicesLocked();
            mNeedToSendFinishedDeviceScan = true;

        }

5.5

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