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Re: Dummy pthread functions in libc considered harmful
- From: Alexander Monakov <amonakov at ispras dot ru>
- To: Rich Felker <dalias at libc dot org>
- Cc: Ondřej Bílka <neleai at seznam dot cz>, Samuel Thibault <samuel dot thibault at ens-lyon dot org>, Andreas Schwab <schwab at suse dot de>, libc-alpha at sourceware dot org
- Date: Mon, 31 Aug 2015 17:54:46 +0300 (MSK)
- Subject: Re: Dummy pthread functions in libc considered harmful
- Authentication-results: sourceware.org; auth=none
- References: <mvmr3ms4sbj dot fsf at hawking dot suse dot de> <20150824153816 dot GC3210 at type dot bordeaux dot inria dot fr> <20150824162250 dot GD32742 at brightrain dot aerifal dot cx> <20150825125035 dot GA3463 at domone> <alpine dot LNX dot 2 dot 20 dot 1508251557030 dot 18864 at monopod dot intra dot ispras dot ru> <20150825143615 dot GH32742 at brightrain dot aerifal dot cx>
On Tue, 25 Aug 2015, Rich Felker wrote:
> > (however when libpthread is not linked in, you know that pthread_mutex_lock is
> > not operating on shared memory: you'd need pthread_mutexattr_setpshared, which
> > is not provided in libc.so.6)
>
> This is false. The process that maps and locks the process-shared
> mutex need not be the one that called pthread_mutex_init. I ran into
> this issue when optimizing static linking; you can't omit
> process-shared code when the program doesn't reference
> pthread_mutexattr_setpshared, because it could get the mutex from
> another program -- that's the whole point of having it be
> process-shared.
As a result, a libc "stub" mutex must:
- contain a full implementation for process-shared mutexes
- for non-shared mutexes in single-threaded processes, modify them
consistently with non-stub implementation (but modifications need not be
atomic)
Does Glibc do the former? (the bug report is about Glibc not doing the latter)
Alexander