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Boost-Commit : |
From: bdawes_at_[hidden]
Date: 2007-10-08 13:58:50
Author: bemandawes
Date: 2007-10-08 13:58:49 EDT (Mon, 08 Oct 2007)
New Revision: 39811
URL: http://svn.boost.org/trac/boost/changeset/39811
Log:
thread16 - update effects for try_lock and timed_lock as per Hans Boehm
Text files modified:
sandbox/committee/LWG/thread_library.html | 37 ++++++++++++++++++++++++++++++-------
1 files changed, 30 insertions(+), 7 deletions(-)
Modified: sandbox/committee/LWG/thread_library.html
==============================================================================
--- sandbox/committee/LWG/thread_library.html (original)
+++ sandbox/committee/LWG/thread_library.html 2007-10-08 13:58:49 EDT (Mon, 08 Oct 2007)
@@ -2,7 +2,7 @@
<html lang="en"><head>
- <meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>Thread Working Draft 15</title>
+ <meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>Thread Working Draft 16</title>
<style>
p {text-align:justify}
@@ -888,8 +888,21 @@
<i>Precondition:</i> For non-recursive mutexes the current thread of execution shall not own the mutex.
</p>
<p>
-<i>Effects:</i> If ownership can be obtained without blocking, then ownership is obtained,
-else there is no effect and <tt>try_lock()</tt> immediately returns.
+<i>Effects:</i>
+If ownership can be obtained without blocking,
+then an attempt is made to obtain ownership.
+If ownership is not obtained,
+there is no effect and <code>try_lock()</code> immediately returns.
+[<i>Note:</i> It is expected that <code>try_lock()</code> almost
+always obtains ownership if the lock is available,
+but it is not guaranteed that it always does so.
+Since a failed <code>try_lock()</code> is not an acquire operation [1.10],
+the resulting memory visibility rules are weak enough
+that they would render such a guarantee essentially useless.
+And such a guarantee would preclude potentially interesting
+<code>try_lock()</code> implementations based on <code>compare_swap</code>.
+— <i>end note</i>]
+
</p>
<p>
<i>Returns:</i> <tt>true</tt> if ownership was obtained, otherwise <tt>false</tt>.
@@ -1043,10 +1056,20 @@
<b>[Crowl: Roundup here instead of under various locks.]</b>
</p>
<p>
-<i>Effects:</i> The function attempts to obtain ownership of the mutex within the specified time.
-If the indicated time is less than or equal to <tt>0</tt>, the function still attempts to obtain ownership without
-blocking (as if by calling <tt>try_lock()</tt>). If the function returns within the specified
-time duration, it shall have obtained ownership.
+<i>Effects:</i>
+The function attempts to obtain ownership of the mutex
+within the specified time.
+If the indicated time is less than or equal to <tt>0</tt>,
+the function still attempts to obtain ownership without
+blocking (as if by calling <tt>try_lock()</tt>).
+If the function returns within the specified time duration,
+it shall have obtained ownership.
+[<i>Note:</i>
+As with <code>try_lock()</code>,
+there is no guarantee that ownership will be obtained
+if the lock is available,
+but implementations are expected to make a strong effort to do so.
+— <i>end note</i>]
</p>
<p>
<i>Returns:</i> <tt>true</tt> if ownership was obtained, otherwise <tt>false</tt>.
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