C++ 睡眠函数

问题描述

我正在尝试执行一个有点准确的睡眠功能.我测量了我的睡眠功能睡了多长时间并将它们并排放置.下面示例的格式是:预期毫秒:结果毫秒".

I am trying to execute a sleep function that is somewhat accurate. I measured how long my sleep function slept for and put them side by side. The format for the samples down below are: "expected ms:outcome ms".

我尝试了很多选项，但仍然找不到解决方案.以下是我尝试过的路线:

I have tried many options and I still can't find a solution. Here are the routes I tried:

Sleep(<time>)

/* milliseconds */
38.4344 46.4354
41.728 47.7818
0.556 0.0012
43.6532 46.8087
0.4523 0.0009
62.8664 76.995
1.5363 15.4592
75.9435 78.1663
91.5194 92.0786
0.6533 0.001
39.7423 45.6729
0.5022 0.0008
54.7837 60.597
0.4248 0.0011
39.2165 45.6977
0.4854 0.0008
10.6741 15.054

• 几乎没有明显的 CPU 使用率，这很好，但结果仍然不准确.

/* Windows sleep in 100ns units */
BOOLEAN nanosleep(LONGLONG ns){
    /* Declarations */
    HANDLE timer;   /* Timer handle */
    LARGE_INTEGER li;   /* Time defintion */
    /* Create timer */
    if(!(timer = CreateWaitableTimer(NULL, TRUE, NULL)))
        return FALSE;
    /* Set timer properties */
    li.QuadPart = -ns;
    if(!SetWaitableTimer(timer, &li, 0, NULL, NULL, FALSE)){
        CloseHandle(timer);
        return FALSE;
    }
    /* Start & wait for timer */
    WaitForSingleObject(timer, INFINITE);
    /* Clean resources */
    CloseHandle(timer);
    /* Slept without problems */
    return TRUE;
}

/* milliseconds */
1.057 14.7561
66.5977 79.4437
0.409 14.7597
152.053 156.757
1.26725 15.747
19.025 30.6343
67.3235 78.678
0.4203 14.4713
65.3507 74.4703
0.4525 14.8102
28.6145 29.7099
72.0035 74.7315
0.5971 14.8625
55.7059 59.3889
0.4791 14.5419
50.9913 61.6719
0.5929 15.5558

• CPU 使用率较低，这很好，但仍然不准确.
• 我在某处读到使用多媒体定时器可以提供准确的睡眠.

代码源

void super_sleep(double ms)
{
    auto a = std::chrono::steady_clock::now();
    while ((std::chrono::steady_clock::now() - a) < std::chrono::milliseconds(static_cast<int>(ms))) {
        continue;
    }
}

/* milliseconds */
55.7059 55.0006
0.5669 0.0008
66.5977 66.0009
0.4213 0.0009
0.7228 0.0007
7.5374 7.0006
0.8825 0.0007
0.4143 0.0009
59.8062 59.0005
51.7157 51.0006
54.0807 54.0006
11.8834 11.0006
65.3507 65.0004
14.429 14.0006
0.4452 0.0012
1.6797 1.0004
96.0012 96.0006

• 工作得比其他尝试好很多，但占用了我高达 7% 的 CPU.

我也尝试使用 std::this_thread::sleep_for() 并收到与 Route 2 类似的结果.

I also tried using std::this_thread::sleep_for() and received similar result to Route 2.

我使用的是 Windows 10 20H2、C++17 和 i9 9900k.

I am on Windows 10 20H2, C++17 and i9 9900k.

推荐答案

获得相当良好准确性(但并不完美，因为 Windows 不是实时操作系统)的一种方法是使用一个标准睡眠功能，但睡眠时间短 - 然后忙 - 等待剩余时间.这通常会使 CPU 使用率保持在较低水平.

One way to get pretty good accuracy (but not perfect since Windows isn't a Real Time OS), is to use one of the standard sleep functions, but sleep short - and then busy-wait the remaining time. That usually keeps the CPU usage low.

template<class T, class U>
void Sleep(std::chrono::duration<T,U> ss) {
    auto target = std::chrono::steady_clock::now() + ss; // the target end time

    // Sleep short. 5 ms is just an example. You need to trim that parameter.
    std::this_thread::sleep_until(target - std::chrono::milliseconds(5));

    // busy-wait the remaining time
    while(std::chrono::steady_clock::now() < target) {}
}

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