Question

我在实际的生产代码中使用了以下代码的版本。它在将来的某个时间设置一个等待计时器，然后有一个工作线程等待它触发：

//Create timer
hWTimer = ::CreateWaitableTimer(NULL, FALSE, NULL);

//Number of minutes to wait
int nMinutesToWait = 5;

//Predict when it should fire
COleDateTime dtWhen = COleDateTime::GetCurrentTime() + COleDateTimeSpan(0, 0, nMinutesToWait, 0);

//Set timer
SetWaitableTimerSecondsFromNow(hWTimer, nMinutesToWait * 60);

//Waiting part
if(::WaitForSingleObject(hWTimer, INFINITE) == WAIT_OBJECT_0)
{
    //Timer has fired, compare when
    _TRACE(L"Time scheduled for: %s, time fired: %s", 
        dtWhen.Format(),
        COleDateTime::GetCurrentTime().Format());
}

BOOL SetWaitableTimerSecondsFromNow(HANDLE hWTimer, double fSecs2Wait)
{
    //INFO: I'm setting the timer to a relative time to ensure that it
    //      doesn't fire in case the system clock is adjusted.
    LARGE_INTEGER li;
    li.QuadPart = -10000000LL * (LONGLONG)fSecs2Wait;   //Convert to 100 nanosecond intervals (MUST BE NEGATIVE)
    if(li.QuadPart >= 0)
        return FALSE;

    return ::SetWaitableTimer(hWTimer, &li, 0, NULL, NULL, FALSE);
}

效果很好，在大多数情况下，计时器需要点火的时间和实际点火的时间是100％匹配。但是极少数情况下，计时器会提前10-15秒发射，仅需5分钟。似乎这个问题主要发生在Windows XP上。

有谁知道这里发生了什么以及如何减轻它？

等待计时器参差不齐的精度

0 个答案: