From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 108119 invoked by alias); 10 Apr 2015 08:38:02 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 108017 invoked by uid 89); 10 Apr 2015 08:38:01 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.0 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-Spam-User: qpsmtpd, 2 recipients X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Fri, 10 Apr 2015 08:38:00 +0000 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (Postfix) with ESMTPS id 378F891C06; Fri, 10 Apr 2015 08:37:59 +0000 (UTC) Received: from localhost (ovpn-116-37.ams2.redhat.com [10.36.116.37]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t3A8bvju012747; Fri, 10 Apr 2015 04:37:58 -0400 Date: Fri, 10 Apr 2015 08:38:00 -0000 From: Jonathan Wakely To: Torvald Riegel Cc: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: Re: [patch] Fix shared_timed_mutex::try_lock_until() et al Message-ID: <20150410083757.GV9755@redhat.com> References: <20150407142830.GG9755@redhat.com> <1428512373.924.26.camel@triegel.csb> <20150408191159.GQ9755@redhat.com> <20150408193808.GR9755@redhat.com> <1428624966.924.32.camel@triegel.csb> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <1428624966.924.32.camel@triegel.csb> User-Agent: Mutt/1.5.23 (2014-03-12) X-SW-Source: 2015-04/txt/msg00438.txt.bz2 On 10/04/15 02:16 +0200, Torvald Riegel wrote: >On Wed, 2015-04-08 at 20:38 +0100, Jonathan Wakely wrote: >> On 08/04/15 20:11 +0100, Jonathan Wakely wrote: >> >We can get rid of the _Mutex type then, and just use std::mutex, >> >and that also means we can provide the timed locking functions >> >even when !defined(_GTHREAD_USE_MUTEX_TIMEDLOCK). >> > >> >And so maybe we should use this fallback implementation instead of >> the >> >pthread_rwlock_t one when !defined(_GTHREAD_USE_MUTEX_TIMEDLOCK), >> >so that they have a complete std::shared_timed_mutex (this applies >> >to at least Darwin, not sure which other targets). >> >> Here's a further patch to do that (which really needs to go into >> 5.0 too, so we don't switch Darwin to the new pthread_rwlock_t >> version and then have to swtich it back again in 6.0). > >I understand why a mutex with timeouts isn't required anymore, but >why do you now add it to the USE_PTHREAD_RWLOCK_T condition? If >pthread_rwlock_t is available, why would we need a normal mutex with >timeouts? Darwin and HPUX support pthread_rwlock_t but not the timed lock functions, see https://gcc.gnu.org/PR64847 and (part of) https://gcc.gnu.org/PR64368 which were "fixed" by https://gcc.gnu.org/r220161 which just disables the timed lock functions on those targets, using #if _GTHREAD_USE_MUTEX_TIMEDLOCK. That means Darwin and HPUX have an incomplete shared_timed_mutex that doesn't support the timed functions (i.e. what might get added to C++17 as std::shared_mutex). The patch below gives Darwin and HPUX a fully conforming (albeit slower) shared_timed_mutex, by ensuring we don't use pthread_rwlock_t for targets that can't use timed functions with pthread_rwlock_t. If std::shared_mutex is added to the standard we could use pthread_rwlock_t for that even on Darwin and HPUX, because it provides everything needed for a non-timed std::shared_mutex. >For example, this chunk here (and others too): > >> diff --git a/libstdc++-v3/include/std/shared_mutex b/libstdc >> ++-v3/include/std/shared_mutex >> index 7f26465..351a4f6 100644 >> --- a/libstdc++-v3/include/std/shared_mutex >> +++ b/libstdc++-v3/include/std/shared_mutex >> @@ -57,7 +57,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION >> /// shared_timed_mutex >> class shared_timed_mutex >> { >> -#ifdef _GLIBCXX_USE_PTHREAD_RWLOCK_T >> +#if defined(_GLIBCXX_USE_PTHREAD_RWLOCK_T) && >> _GTHREAD_USE_MUTEX_TIMEDLOCK >> typedef chrono::system_clock __clock_t; >> >> #ifdef PTHREAD_RWLOCK_INITIALIZER >