Clock_gettime () returns about 1-2 ms of inaccuracy every 50-100 ms (Debian wheezy on Virtualbox)

Question

I recently had a closely related thread here .

However, replacing cin.ignore()with usleep(50e3). It does not report exactly every 50 ms. Watch reports

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

As you can see (sorry, but maybe a long conclusion, but just in case), there is a constant inaccuracy.

Why is it that affects it and how can it be fixed?

Answer 1

, sleep, , . .

usleep() useconds, , . , - .

, .

Answer 2

, , .

, " ", " X ", " X ". , , , , , .

, , , , , (, Universal ? ).

Answer 3

( /), , 1 " 0" " 1 ".

MSDN :

(, MSDN ) :

" , . , , (). () (, , , ). . , . . ± 1 , , . . , , .