winapi - WaitForSingleObjectEx 是否允许提前唤醒？

Question

我正在总结一种情况，其中事件超时的 WaitForSingleObjectEx 没有返回“已发出信号”，但超时尚未过去。

具体来说，为了在 Qt 中调试这个问题，我更改了 this code :

bool QMutexPrivate::wait(int timeout)
{
    return (WaitForSingleObjectEx(event, timeout < 0 ? INFINITE : timeout, FALSE) == WAIT_OBJECT_0);
}

此代码(包括测量值):

bool QMutexPrivate::wait(int timeout)
{
    LARGE_INTEGER StartingTime, EndingTime, ElapsedMicroseconds;
    LARGE_INTEGER Frequency;

    QueryPerformanceFrequency(&Frequency);
    QueryPerformanceCounter(&StartingTime);

    auto result = (WaitForSingleObjectEx(event, timeout < 0 ? INFINITE : timeout, FALSE) == WAIT_OBJECT_0);

    QueryPerformanceCounter(&EndingTime);
    ElapsedMicroseconds.QuadPart = EndingTime.QuadPart - StartingTime.QuadPart;

    ElapsedMicroseconds.QuadPart *= 1000000;
    ElapsedMicroseconds.QuadPart /= Frequency.QuadPart;
    if (!result && timeout > 0)
        std::cerr << "Waited for " << ElapsedMicroseconds.QuadPart << " microseconds when asked " << timeout << std::endl;
    return result;
}

其中事件是通过CreateEvent(0, FALSE, FALSE, 0);创建的。

强调此代码路径会打印如下语句:

Waited for 96734 microseconds when asked for 100 msecs

WaitForSingleObjectEx 是否允许提前唤醒，即在指定的超时之前(由于内核中的计时器合并或类似技术)，或者我应该在其他地方调查我的问题？ documentation并不能帮助我澄清这一点。

Answer 1

MSDN 上 Wait Functions and Time-out Intervals :

The accuracy of the specified time-out interval depends on the resolution of the system clock. The system clock "ticks" at a constant rate. If the time-out interval is less than the resolution of the system clock, the wait may time out in less than the specified length of time. If the time-out interval is greater than one tick but less than two, the wait can be anywhere between one and two ticks, and so on.

To increase the accuracy of the time-out interval for the wait functions, call the timeGetDevCaps function to determine the supported minimum timer resolution and the timeBeginPeriod function to set the timer resolution to its minimum. Use caution when calling timeBeginPeriod, as frequent calls can significantly affect the system clock, system power usage, and the scheduler. If you call timeBeginPeriod, call it one time early in the application and be sure to call the timeEndPeriod function at the very end of the application.