Incorrect predictions if code contains usleep calls

[mbUSC]

How to reproduce the problem

1. #define _GNU_SOURCE 1
2. 
3. #include <stdio.h>
4. #include <pthread.h>
5. #include <unistd.h>
6. #include <coz.h>
7. 
8. static const unsigned int NUM_ITERATIONS = 100000;
9. 
10. void* threadA_fn(void* barrier) {
11.     for (int i = 0; i < NUM_ITERATIONS; i++) {
12.         usleep(2500);
13.         pthread_barrier_wait(barrier);
14.         COZ_PROGRESS;
15.     }
16. }
17. 
18. void* threadB_fn(void* barrier) {
19.     for (int i = 0; i < NUM_ITERATIONS; i++) {
20.         usleep(10000);
21.         pthread_barrier_wait(barrier);
22.         COZ_PROGRESS;
23.     }
24. }
25. 
26. int main(void) {
27.     pthread_t threadA;
28.     pthread_t threadB;
29.     pthread_barrier_t barrier;
30. 
31.     pthread_barrier_init(&barrier, NULL, 2);
32. 
33.     pthread_create(&threadA, NULL, threadA_fn, &barrier);
34.     pthread_create(&threadB, NULL, threadB_fn, &barrier);
35. 
36.     pthread_join(threadA, NULL);
37.     pthread_join(threadB, NULL);
38. 
39.     pthread_barrier_destroy(&barrier);
40. }

Environment

Processor: 12th Gen Intel(R) Core(TM) i7-12800H 2.40 GHz
Installed RAM: 32.0 GB (31.6 GB usable)
OS: Windows 11 (WSL)

Results from Coz