[Boost-commit] svn:boost r58094 - trunk/boost

Subject: [Boost-commit] svn:boost r58094 - trunk/boost
From: pdimov_at_[hidden]
Date: 2009-12-02 06:47:58

Author: pdimov
Date: 2009-12-02 06:47:58 EST (Wed, 02 Dec 2009)
New Revision: 58094
URL: http://svn.boost.org/trac/boost/changeset/58094

Log:
Add memory_order_consume.
Text files modified: 
   trunk/boost/memory_order.hpp |    22 ++++++++++++++++++++--                  
   1 files changed, 20 insertions(+), 2 deletions(-)

Modified: trunk/boost/memory_order.hpp
==============================================================================
--- trunk/boost/memory_order.hpp	(original)
+++ trunk/boost/memory_order.hpp	2009-12-02 06:47:58 EST (Wed, 02 Dec 2009)
@@ -11,7 +11,7 @@
 //
 //  Defines enum boost::memory_order per the C++0x working draft
 //
-//  Copyright (c) 2008 Peter Dimov
+//  Copyright (c) 2008, 2009 Peter Dimov
 //
 //  Distributed under the Boost Software License, Version 1.0.
 //  See accompanying file LICENSE_1_0.txt or copy at
@@ -21,13 +21,31 @@
 namespace boost
 {
 
+//
+// Enum values are chosen so that code that needs to insert
+// a trailing fence for acquire semantics can use a single
+// test such as:
+//
+// if( mo & memory_order_acquire ) { ...fence... }
+//
+// For leading fences one can use:
+//
+// if( mo & memory_order_release ) { ...fence... }
+//
+// Architectures such as Alpha that need a fence on consume
+// can use:
+//
+// if( mo & ( memory_order_acquire | memory_order_consume ) ) { ...fence... }
+//
+
 enum memory_order
 {
     memory_order_relaxed = 0,
     memory_order_acquire = 1,
     memory_order_release = 2,
     memory_order_acq_rel = 3, // acquire | release
-    memory_order_seq_cst = 7  // acq_rel | 4
+    memory_order_seq_cst = 7, // acq_rel | 4
+    memory_order_consume = 8
 };
 
 } // namespace boost