From b13b7f3990f5883c4ffc1d8124e1ca84162b68ca Mon Sep 17 00:00:00 2001
From: David Daney <ddaney@caviumnetworks.com>
Date: Tue, 4 Aug 2009 17:25:42 +0000
Subject: [PATCH] mutex.h (gomp_mutex_unlock): Add comment about needed memory
barrier semantics.
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
---
libgomp/ChangeLog | 6 ++++++
libgomp/config/linux/mips/mutex.h | 27 +++++++++++++++++++++++++++
libgomp/config/linux/mutex.h | 10 ++++++++++
3 files changed, 43 insertions(+)
create mode 100644 libgomp/config/linux/mips/mutex.h
diff --git a/libgomp/ChangeLog b/libgomp/ChangeLog
index e10c45589a4e..6b9592bda731 100644
--- a/libgomp/ChangeLog
+++ b/libgomp/ChangeLog
@@ -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.
diff --git a/libgomp/config/linux/mips/mutex.h b/libgomp/config/linux/mips/mutex.h
new file mode 100644
index 000000000000..668cc11b29a9
--- /dev/null
+++ b/libgomp/config/linux/mips/mutex.h
@@ -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"
diff --git a/libgomp/config/linux/mutex.h b/libgomp/config/linux/mutex.h
index 07a2156a4629..1905ce012fde 100644
--- a/libgomp/config/linux/mutex.h
+++ b/libgomp/config/linux/mutex.h
@@ -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);
--
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