如何在 C（Linux）中的 while 循环中准确睡眠？

Question

在 C 代码（Linux 操作系统）中，我需要在一个 while 循环内准确地休眠 - 比如说，10000 微秒，共 1000 次。我试过usleep、nanosleep、select、pselect和其他一些方法都没有成功。 在大约 50 次中，它的睡眠时间会延长 %100（大约 20000 我们）。 我需要在每次延迟后执行一个动作。因此，每个延迟都必须非常准确。 有没有办法为这种情况做准确的睡眠？ 谢谢..

编辑：

#include <stdio.h>
#include <sys/time.h>

int main(int argc, char *argv[]) {
    struct timespec t0, t1;
    long err;
    int i = 0;

    while (i < 1000) {
        clock_gettime(CLOCK_MONOTONIC, &t0);
        usleep(10000);
        clock_gettime(CLOCK_MONOTONIC, &t1);
        err = (long) ((t1.tv_sec - t0.tv_sec) * 1e6
                + (t1.tv_nsec - t0.tv_nsec) / 1000) - 10000;
        printf("i = %d err = %ld\n", i, err);
        i++;
    }

    return 0;
}

结果（日志文件）：

i = 0 err = -146
i = 1 err = -207
i = 2 err = -8
i = 3 err = -4
i = 4 err = -22
i = 5 err = 31
i = 6 err = -45
i = 7 err = 9
i = 8 err = 61
i = 9 err = -71
i = 10 err = -24
i = 11 err = 14
i = 12 err = -12
i = 13 err = -32
i = 14 err = -15
i = 15 错误 = 42
i = 16 错误 = -51
i = 17 错误 = -19
i = 18 错误 = -12
i = 19 错误 = 4
i = 20错误 = 12
i = 21 错误 = -36
i = 22 错误 = -38
i = 23 错误 = 18
i = 24 错误 = 1
i = 25 错误 = - 21
i = 26 err = -37
i = 27 err = 31
i = 28 err = -4
i = 29 err = -45
i = 30 err = -37
i = 31 错误 = 20
i = 32 错误 = -10
i = 33 错误 = -5
i = 34 错误 = -12
i = 35 错误 = -5i = 36 err = -10
i = 37 err = -12
i = 38 err = -2
i = 39 err = 14
i = 40 err = -34
i = 41 错误 = -10
i = 42 错误 = -6
i = 43 错误 = 15
i = 44 错误 = -34
i = 45 错误 = -12
i = 46 错误 = -15
i = 47 错误 = -25
i = 48 错误 = 11614
i = 49 错误 = 2340
i = 50 错误 = 589
i = 5 1 错误 = 12254
i = 52 错误 = -93
i = 53 错误 = -19

Answer 1

睡眠时间较短，然后轮询高频计数器以完成延迟。将所有延迟都基于计数器的原始读数，以防止随时间漂移。例如，previous_count = counter(), wait_count = previous_count + delay_count, delay until counter() - wait_count >= 0, previous_count += delay_count, ... 。如果所需的频率不是 counter() 频率的精确倍数，则使用一个变量来表示延迟的小数部分（我称之为剩余计数）。

由于您提到了 Windows，这里是一个以固定频率运行的线程的示例，并且与 Windows XP 兼容，其中 Sleep(1) 最多可能需要 2 毫秒。 dwLateStep 是一种调试辅助工具，每次循环时间过长时都会增加（如果可能，它会赶上）。延迟基于计数器的原始读数（使用 uWait、uRem、uPrev、uDelta），因此在很长一段时间内没有漂移。这基本上是游戏实现固定频率物理线程的方式。请注意，.net 框架不用于这些类型的游戏，因为它会间歇性地暂停进程以重新打包分页内存。此类游戏会将物理线程优先级设置为高于正常水平，以防止其他线程或进程对其进行干扰。

typedef unsigned long long UI64;        /* unsigned 64 bit int */
#define FREQ    400                     /* frequency */
DWORD    dwLateStep;                    /* late step count */
LARGE_INTEGER liPerfFreq;               /* 64 bit frequency */
LARGE_INTEGER liPerfTemp;               /* used for query */
UI64 uFreq = FREQ;                      /* process frequency */
UI64 uOrig;                             /* original tick */
UI64 uWait;                             /* tick rate / freq */
UI64 uRem = 0;                          /* tick rate % freq */
UI64 uPrev;                             /* previous tick based on original tick */
UI64 uDelta;                            /* current tick - previous */
UI64 u2ms;                              /* 2ms of ticks */
UI64 i;

    /* ... */ /* wait for some event to start thread */
    QueryPerformanceFrequency(&liPerfFreq);
    u2ms = ((UI64)(liPerfFreq.QuadPart)+499) / ((UI64)500);

    timeBeginPeriod(1);                 /* set period to 1ms */
    Sleep(128);                         /* wait for it to stabilize */

    QueryPerformanceCounter((PLARGE_INTEGER)&liPerfTemp);
    uOrig = uPrev = liPerfTemp.QuadPart;

    for(i = 0; i < (uFreq*30); i++){
        /* update uWait and uRem based on uRem */
        uWait = ((UI64)(liPerfFreq.QuadPart) + uRem) / uFreq;
        uRem  = ((UI64)(liPerfFreq.QuadPart) + uRem) % uFreq;
        /* wait for uWait ticks */
        while(1){
            QueryPerformanceCounter((PLARGE_INTEGER)&liPerfTemp);
            uDelta = (UI64)(liPerfTemp.QuadPart - uPrev);
            if(uDelta >= uWait)
                break;
            if((uWait - uDelta) > u2ms)
                Sleep(1);
        }
        if(uDelta >= (uWait*2))
            dwLateStep += 1;
        uPrev += uWait;
        /* fixed frequency code goes here */
        /*  along with some type of break when done */
        /*  otherwise, this example runs for 30 seconds */
    }

    timeEndPeriod(1);                   /* restore period */