How to use nanosleep() in C? What are `tim.tv_sec` and `tim.tv_nsec`?

tv_nsec is the sleep time in nanoseconds. 500000us = 500000000ns, so you want:

nanosleep((const struct timespec[]){{0, 500000000L}}, NULL);

500000 microseconds are 500000000 nanoseconds. You only wait for 500 ns = 0.5 µs.

Half a second is 500,000,000 nanoseconds, so your code should read:

tim.tv_sec  = 0;
tim.tv_nsec = 500000000L;

As things stand, you code is sleeping for 1.0000005s (1s + 500ns).

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