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 [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 0E4613857C48 for ; Tue, 17 May 2022 19:56:39 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 0E4613857C48 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-175-sn_W377PO9uF9-gyBzDBnQ-1; Tue, 17 May 2022 15:56:35 -0400 X-MC-Unique: sn_W377PO9uF9-gyBzDBnQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2784D395AFE5; Tue, 17 May 2022 19:56:35 +0000 (UTC) Received: from localhost (unknown [10.33.36.185]) by smtp.corp.redhat.com (Postfix) with ESMTP id E2EF3492C14; Tue, 17 May 2022 19:56:34 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Cc: Thomas Rodgers Subject: [committed] libstdc++: Relax memory ordering for default memory resource object Date: Tue, 17 May 2022 20:56:34 +0100 Message-Id: <20220517195634.164341-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) 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, 17 May 2022 19:56:40 -0000 Tested powerpc64le-linux, pushed to trunk. -- >8 -- Currently pmr::set_default_resource and pmr::get_default_resource both use sequentially consistent memory ordering. This is overkill. The standard only requires that a call to set_default_resource synchronizes with subsequent calls to set_default_resource and get_default_resource. Using acquire-release for the setter and acquire for the getter is sufficient to meet the requirement. Reviewed-by: Thomas Rodgers libstdc++-v3/ChangeLog: * src/c++17/memory_resource.cc (set_default_resource): Use memory_order_acq_rel. (get_default_resource): Use memory_order_acquire. --- libstdc++-v3/src/c++17/memory_resource.cc | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc index bb6334c9694..8bc55a69f1f 100644 --- a/libstdc++-v3/src/c++17/memory_resource.cc +++ b/libstdc++-v3/src/c++17/memory_resource.cc @@ -112,13 +112,13 @@ namespace pmr mutex mx; memory_resource* val; - memory_resource* load() + memory_resource* load(std::memory_order) { lock_guard lock(mx); return val; } - memory_resource* exchange(memory_resource* r) + memory_resource* exchange(memory_resource* r, std::memory_order) { lock_guard lock(mx); return std::__exchange(val, r); @@ -134,12 +134,12 @@ namespace pmr memory_resource* val; - memory_resource* load() const + memory_resource* load(std::memory_order) const { return val; } - memory_resource* exchange(memory_resource* r) + memory_resource* exchange(memory_resource* r, std::memory_order) { return std::__exchange(val, r); } @@ -166,12 +166,12 @@ namespace pmr { if (r == nullptr) r = new_delete_resource(); - return default_res.obj.exchange(r); + return default_res.obj.exchange(r, std::memory_order_acq_rel); } memory_resource* get_default_resource() noexcept - { return default_res.obj.load(); } + { return default_res.obj.load(std::memory_order_acquire); } // Member functions for std::pmr::monotonic_buffer_resource -- 2.34.3