* nice standards complaince issue
@ 2013-04-13 22:23 Justin Cormack
2013-04-15 1:45 ` Rich Felker
0 siblings, 1 reply; 3+ messages in thread
From: Justin Cormack @ 2013-04-13 22:23 UTC (permalink / raw)
To: musl
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According to the man page, Musl nice is not compliant, it is defined to
return 0 if successful
int nice(int inc)
{
#ifdef SYS_nice
return syscall(SYS_nice, inc);
#else
return setpriority(PRIO_PROCESS, 0, getpriority(PRIO_PROCESS,
0)+inc);
#endif
}
However the manpage says it is required to return the new value:
SUSv2 and POSIX.1-2001 specify that nice() should return the new nice
value. However, the Linux syscall and the nice() library function
provided in older versions of (g)libc (earlier than glibc 2.2.4) return 0
on success. The new nice value can be found using getpriority(2).
Since glibc 2.2.4, nice() is implemented as a library function that calls
getpriority(2) to obtain the new nice value to be returned to the
caller. With this implementation, a successful call can legitimately
return -1. To reliably detect an error, set errno to 0 before the call,
and check its value when nice() returns -1.
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: nice standards complaince issue
2013-04-13 22:23 nice standards complaince issue Justin Cormack
@ 2013-04-15 1:45 ` Rich Felker
2013-04-15 7:31 ` Justin Cormack
0 siblings, 1 reply; 3+ messages in thread
From: Rich Felker @ 2013-04-15 1:45 UTC (permalink / raw)
To: musl
On Sat, Apr 13, 2013 at 11:23:08PM +0100, Justin Cormack wrote:
> Since glibc 2.2.4, nice() is implemented as a library function that calls
> getpriority(2) to obtain the new nice value to be returned to the
> caller. With this implementation, a successful call can legitimately
> return -1. To reliably detect an error, set errno to 0 before the call,
> and check its value when nice() returns -1.
Thanks for the heads-up. Actually, I think there's a much bigger issue
with both nice and setpriority: they're affecting one thread rather
than the process. This may technically not be non-conforming as long
as SCHED_OTHER scheduling is in effect, but it's sketchy. Basically
this all stems from a complete failure of Linux to support process
contention scope and the [PS] option of POSIX... (despite glibc
claiming to support it!)
In any case, the issue you reported should be fixed. Do you have a
proposed patch?
Rich
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: nice standards complaince issue
2013-04-15 1:45 ` Rich Felker
@ 2013-04-15 7:31 ` Justin Cormack
0 siblings, 0 replies; 3+ messages in thread
From: Justin Cormack @ 2013-04-15 7:31 UTC (permalink / raw)
To: musl
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On Mon, Apr 15, 2013 at 2:45 AM, Rich Felker <dalias@aerifal.cx> wrote:
> On Sat, Apr 13, 2013 at 11:23:08PM +0100, Justin Cormack wrote:
> > Since glibc 2.2.4, nice() is implemented as a library function that calls
> > getpriority(2) to obtain the new nice value to be returned to the
> > caller. With this implementation, a successful call can legitimately
> > return -1. To reliably detect an error, set errno to 0 before the call,
> > and check its value when nice() returns -1.
>
> Thanks for the heads-up. Actually, I think there's a much bigger issue
> with both nice and setpriority: they're affecting one thread rather
> than the process. This may technically not be non-conforming as long
> as SCHED_OTHER scheduling is in effect, but it's sketchy. Basically
> this all stems from a complete failure of Linux to support process
> contention scope and the [PS] option of POSIX... (despite glibc
> claiming to support it!)
>
> In any case, the issue you reported should be fixed. Do you have a
> proposed patch?
>
Something like
--- src/unistd/nice.c-old 2013-04-15 08:16:06.855064898 +0100
+++ src/unistd/nice.c 2013-04-15 08:21:55.920848795 +0100
@@ -3,10 +3,11 @@
#include "syscall.h"
int nice(int inc)
-{
#ifdef SYS_nice
- return syscall(SYS_nice, inc);
+ int ret = syscall(SYS_nice, inc);
#else
- return setpriority(PRIO_PROCESS, 0, getpriority(PRIO_PROCESS, 0)+inc);
+ int ret = setpriority(PRIO_PROCESS, 0, getpriority(PRIO_PROCESS, 0)+inc);
#endif
+ if (ret < 0) return ret;
+ return 20-getpriority(PRIO_PROCESS, 0);
}
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