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0 pointsigravious16y ago0 comments

Excuse my ignorance: what do you mean by noisy?

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4 comments · 1 top-level

mustpax16y ago· 3 in thread

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.

tptacek16y ago

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.

xpaulbettsx16y ago

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

mustpax16y ago

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.

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