[mustpax]

Noisy means there is a lot of variance in the actual time the process spends sleeping. When you say sleep(1) most OSes interpret that as saying, sleep as short as you can. Based on the scheduler internals, that can vary a lot.

[tptacek]

Which OS interprets sleep(1) (ie, "sleep for 1 second") as "sleep for as short as you can"?

On WinAPI, Sleep is denominated in milliseconds.

On BSD, sleep(3) is a library wrapper around nanosleep(2).

Linux's man pages make no mention of the magic number "1" as a "sleep 1 timeslice" shortcut; also, older Linux man pages warn that sleep(3) can be implemented in terms of alarm(1), which is used all over POSIX as an I/O timeout and would blow up the world if it alarmed in milliseconds.

If you want to sleep "as short as you can", sleep for 0 seconds, or call any other system call to yield your process back to the scheduler.

[xpaulbettsx]

Windows also only guarantees that your process will sleep at least as long as you specify. Not that it will sleep exactly as long.

[mustpax]

Thanks for the correction. I was just talking about the de facto behavior I have seen on Linux and BSD for very short sleep intervals (way shorter than 1 second), not necessarily about the behavior as specified by the system call. I should have been clearer.

[tptacek]

I really don't think you've ever seen BSD return in milliseconds after a 1-second sleep. Respectfully, I think you're pretty much just wrong.

[mustpax]

Well, that is not what I meant at all, I meant that I've seen BSD return in say 2 microseconds after calling usleep(1).

But that's usleep not sleep, which is the inaccuracy I was admitting to in the first place.

[tptacek]

Ok, but (a) this article is talking about literally POSIX sleep(3), and (b) there is a ton of confusion on this thread about whether sleep is ms-denominated or seconds-denominated.

Sorry to pile on you, though.

[Dylan16807]

Read it again. He's talking about near-zero sleep calls, not one second sleep calls.

[tptacek]

POSIX sleep() doesn't take subsecond intervals. Maybe he's talking about usleep()?