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mutex.h (gomp_mutex_unlock): Add comment about needed memory barrier semantics.

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2009-08-04  David Daney  <ddaney@caviumnetworks.com>

	* config/linux/mutex.h (gomp_mutex_unlock): Add comment about
	needed memory barrier semantics.
	* config/linux/mips/mutex.h: New file.

From-SVN: r150463
This commit is contained in:
David Daney 2009-08-04 17:25:42 +00:00 committed by David Daney
parent 481817e4b9
commit b13b7f3990
3 changed files with 43 additions and 0 deletions
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6
libgomp/ChangeLog
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@ -1,3 +1,9 @@
2009-08-04 David Daney <ddaney@caviumnetworks.com>
* config/linux/mutex.h (gomp_mutex_unlock): Add comment about
needed memory barrier semantics.
* config/linux/mips/mutex.h: New file.
2009-07-30 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
* configure.ac (_AC_ARG_VAR_PRECIOUS): Use m4_rename_force.

27
libgomp/config/linux/mips/mutex.h Normal file
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@ -0,0 +1,27 @@
/* Copyright (C) 2009 Free Software Foundation, Inc.
This file is part of the GNU OpenMP Library (libgomp).
Libgomp is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
/* MIPS needs the same correct usage of __sync_synchronize and
__sync_lock_test_and_set as ia64. So we just use its mutex.h. */
#include "config/linux/ia64/mutex.h"

10
libgomp/config/linux/mutex.h
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@ -48,6 +48,16 @@ static inline void gomp_mutex_lock (gomp_mutex_t *mutex)
extern void gomp_mutex_unlock_slow (gomp_mutex_t *mutex);
static inline void gomp_mutex_unlock (gomp_mutex_t *mutex)
{
/* Warning: By definition __sync_lock_test_and_set() does not have
proper memory barrier semantics for a mutex unlock operation.
However, this default implementation is written assuming that it
does, which is true for some targets.
Targets that require additional memory barriers before
__sync_lock_test_and_set to achieve the release semantics of
mutex unlock, are encouraged to include
"config/linux/ia64/mutex.h" in a target specific mutex.h instead
of using this file. */
int val = __sync_lock_test_and_set (mutex, 0);
if (__builtin_expect (val > 1, 0))
gomp_mutex_unlock_slow (mutex);