From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-398018-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 19685 invoked by alias); 6 Aug 2012 04:19:35 -0000
Received: (qmail 19675 invoked by uid 22791); 6 Aug 2012 04:19:30 -0000
X-SWARE-Spam-Status: No, hits=-3.6 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 06 Aug 2012 04:19:17 +0000
From: "architectbum at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/54185] New: condition_variable not properly destructed
Date: Mon, 06 Aug 2012 04:19:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: architectbum at hotmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-54185-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
X-SW-Source: 2012-08/txt/msg00290.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54185

             Bug #: 54185
           Summary: condition_variable not properly destructed
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: architectbum@hotmail.com


Created attachment 27947
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27947
a possible patch to solve the problem

The c11 standard (draft 3337, paragraph 30.5.1.5) states that
condition_variable may be destructed even if not all wait() calls have
returned, so long as all of those calls are blocking on the associated lock
rather than on *this. However, in gcc 4.7.1 the following snippets sometimes
fail with a segfault in thread A or simply inconsistent results:
  condition_variable *volatile cond = new condition_variable;
  // in thread A
    cond->wait();
  // in thread B, later
    cond->notify_all();
    delete cond;

It appears that the underlying libpthread also allows the destruction of cond
immediately after all blocking threads have been notified, by means of a block
in __pthread_cond_destroy while all of the wait() calls wake and begin to
reacquire their locks.

However, the current implementation in condition_variable.cc uses a default
destructor:
  condition_variable::~condition_variable() noexcept = default;
rather than calling __gthread_cond_destroy, and therefore the pthread cond
object is deleted without the block provided by __pthread_cond_destroy.

The attached patch seems to fix the problem with gcc-4.7.1 (verified on my
system, x86_64-pc-linux-gnu).

The patch undoes the replacement (in the presence of __GTHREAD_COND_INIT) of
~condition_variable with "= default" from
http://gcc.gnu.org/viewcvs?view=revision&revision=180411, which seems to have
been inadvertent.