c++ - clock_gettime() 每 50-100 毫秒返回大约 1-2 毫秒的误差(Virtualbox 上的 Debian wheezy)

Question

前一段时间我有一个密切相关的线程here .

但是，将 cin.ignore() 替换为 usleep(50e3)。它不会准确地每 50 毫秒报告一次。时钟报告

Time Passed:    s: 0 ms: 50
Time Passed:    s: 0 ms: 101
Time Passed:    s: 0 ms: 152
Time Passed:    s: 0 ms: 202
Time Passed:    s: 0 ms: 252
Time Passed:    s: 0 ms: 303
Time Passed:    s: 0 ms: 353
Time Passed:    s: 0 ms: 403
Time Passed:    s: 0 ms: 454
Time Passed:    s: 0 ms: 504
Time Passed:    s: 0 ms: 554
Time Passed:    s: 0 ms: 605
Time Passed:    s: 0 ms: 657
Time Passed:    s: 0 ms: 708
Time Passed:    s: 0 ms: 758
Time Passed:    s: 0 ms: 808
Time Passed:    s: 0 ms: 862
Time Passed:    s: 0 ms: 915
Time Passed:    s: 0 ms: 965
Time Passed:    s: 1 ms: 15
Time Passed:    s: 1 ms: 66
Time Passed:    s: 1 ms: 116
Time Passed:    s: 1 ms: 169
Time Passed:    s: 1 ms: 221
Time Passed:    s: 1 ms: 271
Time Passed:    s: 1 ms: 322
Time Passed:    s: 1 ms: 372
Time Passed:    s: 1 ms: 423
Time Passed:    s: 1 ms: 473
Time Passed:    s: 1 ms: 524
Time Passed:    s: 1 ms: 574
Time Passed:    s: 1 ms: 625
Time Passed:    s: 1 ms: 676
Time Passed:    s: 1 ms: 727
Time Passed:    s: 1 ms: 778
Time Passed:    s: 1 ms: 833
Time Passed:    s: 1 ms: 883
Time Passed:    s: 1 ms: 935
Time Passed:    s: 1 ms: 986
Time Passed:    s: 2 ms: 37
Time Passed:    s: 2 ms: 91
Time Passed:    s: 2 ms: 142
Time Passed:    s: 2 ms: 192
Time Passed:    s: 2 ms: 243
Time Passed:    s: 2 ms: 294
Time Passed:    s: 2 ms: 346
Time Passed:    s: 2 ms: 396
Time Passed:    s: 2 ms: 450
Time Passed:    s: 2 ms: 501
Time Passed:    s: 2 ms: 552
Time Passed:    s: 2 ms: 602
Time Passed:    s: 2 ms: 652
Time Passed:    s: 2 ms: 703
Time Passed:    s: 2 ms: 753
Time Passed:    s: 2 ms: 804
Time Passed:    s: 2 ms: 855
Time Passed:    s: 2 ms: 906
Time Passed:    s: 2 ms: 956
Time Passed:    s: 3 ms: 7
Time Passed:    s: 3 ms: 57
Time Passed:    s: 3 ms: 107
Time Passed:    s: 3 ms: 158
Time Passed:    s: 3 ms: 208
Time Passed:    s: 3 ms: 258
Time Passed:    s: 3 ms: 315
Time Passed:    s: 3 ms: 365
Time Passed:    s: 3 ms: 416
Time Passed:    s: 3 ms: 466
Time Passed:    s: 3 ms: 517
Time Passed:    s: 3 ms: 567
Time Passed:    s: 3 ms: 618
Time Passed:    s: 3 ms: 668
Time Passed:    s: 3 ms: 719
Time Passed:    s: 3 ms: 769
Time Passed:    s: 3 ms: 824
Time Passed:    s: 3 ms: 875
Time Passed:    s: 3 ms: 926
Time Passed:    s: 3 ms: 976
Time Passed:    s: 4 ms: 27
Time Passed:    s: 4 ms: 79
Time Passed:    s: 4 ms: 129
Time Passed:    s: 4 ms: 182
Time Passed:    s: 4 ms: 233
Time Passed:    s: 4 ms: 283
Time Passed:    s: 4 ms: 334
Time Passed:    s: 4 ms: 384
Time Passed:    s: 4 ms: 436
Time Passed:    s: 4 ms: 486
Time Passed:    s: 4 ms: 537
Time Passed:    s: 4 ms: 587
Time Passed:    s: 4 ms: 638
Time Passed:    s: 4 ms: 688
Time Passed:    s: 4 ms: 739
Time Passed:    s: 4 ms: 789
Time Passed:    s: 4 ms: 844
Time Passed:    s: 4 ms: 895
Time Passed:    s: 4 ms: 946
Time Passed:    s: 4 ms: 997
Time Passed:    s: 5 ms: 47
Time Passed:    s: 5 ms: 101
Time Passed:    s: 5 ms: 151
Time Passed:    s: 5 ms: 202
Time Passed:    s: 5 ms: 252
Time Passed:    s: 5 ms: 303
Time Passed:    s: 5 ms: 354
Time Passed:    s: 5 ms: 404
Time Passed:    s: 5 ms: 455

如您所见(抱歉，输出可能很长，但以防万一)，始终存在不准确性。

为什么会这样，有什么影响，如何解决？

Answer 1

当您的进程通过调用 sleep 函数进入休眠状态时，系统调度程序会推迟唤醒它，直到请求的时间耗尽。之后它可能唤醒进程或者可能需要更长的时间。

The usleep() function will cause the calling thread to be suspended from execution until either the number of real-time microseconds specified by the argument useconds has elapsed or a signal is delivered to the calling thread and its action is to invoke a signal-catching function or to terminate the process. The suspension time may be longer than requested due to the scheduling of other activity by the system.

许多操作系统不保证它们会在 sleep 时间结束后立即唤醒进程。