Date: Thu, 28 Feb 2013 09:50:01 GMT From: Mark Linimon <linimon@lonesome.com> To: freebsd-threads@FreeBSD.org Subject: Re: misc/150959: [libc] Stub pthread_once in libc should call _libc_once] Message-ID: <201302280950.r1S9o10K028610@freefall.freebsd.org>
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The following reply was made to PR threads/150959; it has been noted by GNATS.
From: Mark Linimon <linimon@lonesome.com>
To: bug-followup@FreeBSD.org
Cc:
Subject: Re: misc/150959: [libc] Stub pthread_once in libc should call
_libc_once]
Date: Thu, 28 Feb 2013 03:46:03 -0600
apparently this email never made it into the audit-trail
----- Forwarded message from John Baldwin <jhb@freebsd.org> -----
Date: Mon, 27 Sep 2010 11:46:27 -0400
From: John Baldwin <jhb@freebsd.org>
To: freebsd-threads@freebsd.org
Cc: arundel@freebsd.org, freebsd-bugs@freebsd.org
Subject: Re: misc/150959: [libc] Stub pthread_once in libc should call
_libc_once
User-Agent: KMail/1.13.5 (FreeBSD/7.3-CBSD-20100819; KDE/4.4.5; amd64; ; )
On Sunday, September 26, 2010 1:11:52 pm arundel@freebsd.org wrote:
> Old Synopsis: Stub pthread_once in libc should call _libc_once
> New Synopsis: [libc] Stub pthread_once in libc should call _libc_once
>
> Responsible-Changed-From-To: freebsd-bugs->freebsd-threads
> Responsible-Changed-By: arundel
> Responsible-Changed-When: Sun Sep 26 17:08:28 UTC 2010
> Responsible-Changed-Why:
> Over to maintainer(s).
As you note in the history, libstdc++ depends on this behavior, so it is not
likely to be changed. Possibly changing the stub to always return an error
would be ok, except that POSIX defines no errors for pthread_once(). Note
that this behavior also matches Solaris apparently:
(From /usr/include/c++/4.2/bits/gthr-default.h)
#if __GXX_WEAK__ && _GLIBCXX_GTHREAD_USE_WEAK
/* On Solaris 2.6 up to 9, the libc exposes a POSIX threads interface even if
-pthreads is not specified. The functions are dummies and most return an
error value. However pthread_once returns 0 without invoking the routine
it is passed so we cannot pretend that the interface is active if -pthreads
is not specified. On Solaris 2.5.1, the interface is not exposed at all so
we need to play the usual game with weak symbols. On Solaris 10 and up, a
working interface is always exposed. On FreeBSD 6 and later, libc also
exposes a dummy POSIX threads interface, similar to what Solaris 2.6 up
to 9 does. FreeBSD >= 700014 even provides a pthread_cancel stub in libc,
which means the alternate __gthread_active_p below cannot be used there.
*/
#if defined(__FreeBSD__) || (defined(__sun) && defined(__svr4__))
To be honest, I would favor libc exporting '__isthreaded' in some fashion so
that libstdc++ could depend on that instead. I think the symbol is already
public so that libthr can set it.
--
John Baldwin
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