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Date: Mon, 29 Feb 2016 23:59:20 -0500
From: Rich Felker <dalias@...c.org>
To: James Marshall <jcmarsh@...ail.gwu.edu>
Cc: musl@...ts.openwall.com
Subject: Re: sched_* implemented?
On Mon, Feb 29, 2016 at 11:32:34PM -0500, James Marshall wrote:
> Hi,
>
> I'm working on a realtime application and am trying to use musl. I would
> like to call sched_setscheduler, but it looks like this is just a stub in
> musl.
>
> However,
> http://nsz.repo.hu/git/?p=musl-tables;a=blob_plain;f=tab_posix.html;hb=HEAD
> has it marked as implemented. Am I missing something? Is there a patch
> available?
>
> If there is not, any idea of how difficult it would be for me to add it in?
> Or would I be better off using syscall directly instead?
>
> Your help and time is appreciated.
The reason it doesn't do anything is that Linux does not provide a way
to set scheduling parameters for a _process_, only for threads. The
sched_setscheduler syscall is documented as taking a pid but actually
takes a thread id and only operates on that thread. glibc just ignores
this and provides sched_* functions that do the wrong thing.
Fortunately there's an easy fix: use pthread_setschedparam, and
pthread_self to get the pthread_t value you need to pass to it.
Rich
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