From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id 6FCD6385780F for ; Tue, 20 Apr 2021 13:39:03 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 6FCD6385780F Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-547-O9OPD412M1OyhHaRzwgqHA-1; Tue, 20 Apr 2021 09:39:01 -0400 X-MC-Unique: O9OPD412M1OyhHaRzwgqHA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 93ED4881E1D; Tue, 20 Apr 2021 13:38:03 +0000 (UTC) Received: from localhost (unknown [10.33.36.164]) by smtp.corp.redhat.com (Postfix) with ESMTP id 39BB519D9B; Tue, 20 Apr 2021 13:38:03 +0000 (UTC) Date: Tue, 20 Apr 2021 14:38:02 +0100 From: Jonathan Wakely To: Thomas Rodgers Cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org, trodgers@redhat.com, Thomas Rodgers Subject: Re: [PATCH] [libstdc++] Refactor/cleanup of atomic wait implementation Message-ID: <20210420133802.GL3008@redhat.com> References: <20210415124617.GN3008@redhat.com> <20210419192305.406972-1-rodgert@appliantology.com> MIME-Version: 1.0 In-Reply-To: <20210419192305.406972-1-rodgert@appliantology.com> X-Clacks-Overhead: GNU Terry Pratchett X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline X-Spam-Status: No, score=-8.0 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libstdc++@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++ mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 20 Apr 2021 13:39:08 -0000 On 19/04/21 12:23 -0700, Thomas Rodgers wrote: >+ struct __timed_backoff_spin_policy >+ { >+ __wait_clock_t::time_point _M_deadline; >+ __wait_clock_t::time_point _M_t0; >+ >+ template >+ __timed_backoff_spin_policy(chrono::time_point<_Clock, _Dur> >+ __deadline = _Clock::time_point::max(), >+ chrono::time_point<_Clock, _Dur> >+ __t0 = _Clock::now()) noexcept >+ : _M_deadline(__to_wait_clock(__deadline)) >+ , _M_t0(__to_wait_clock(__t0)) >+ { } >+ >+ bool >+ operator()() const noexcept > { >- static_assert(sizeof(__timed_waiters) == sizeof(__waiters)); >- return static_cast<__timed_waiters&>(__waiters::_S_for(__t)); >+ using namespace literals::chrono_literals; >+ auto __now = __wait_clock_t::now(); >+ if (_M_deadline <= __now) >+ return false; >+ >+ auto __elapsed = __now - _M_t0; >+ if (__elapsed > 128ms) >+ { >+ this_thread::sleep_for(64ms); >+ } >+ else if (__elapsed > 64us) >+ { >+ this_thread::sleep_for(__elapsed / 2); >+ } >+ else if (__elapsed > 4us) >+ { >+ __thread_yield(); >+ } >+ else >+ return false; Ah, the reason for some of the time outs I'm seeing is that this function doesn't return anything! /home/jwakely/gcc/12/include/c++/12.0.0/bits/atomic_timed_wait.h: In member function 'bool std::__detail::__timed_backoff_spin_policy::operator()() const': /home/jwakely/gcc/12/include/c++/12.0.0/bits/atomic_timed_wait.h:259:7: warning: control reaches end of non-void function [-Wreturn-type] 259 | } | ^ Should it return true if it waited?