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GET /api/1.2/patches/2226286/?format=api
{ "id": 2226286, "url": "http://patchwork.ozlabs.org/api/1.2/patches/2226286/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.12@forge-stage.sourceware.org/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/1.2/projects/17/?format=api", "name": "GNU Compiler Collection", "link_name": "gcc", "list_id": "gcc-patches.gcc.gnu.org", "list_email": "gcc-patches@gcc.gnu.org", "web_url": null, "scm_url": null, "webscm_url": null, "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.12@forge-stage.sourceware.org>", "list_archive_url": null, "date": "2026-04-22T10:44:27", "name": "[v1,12/16] libstdc++: Optimise std::latch::arrive_and_wait", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "9e45f3c0e20e7eaa31157a43c7198ed3cb78977d", "submitter": { "id": 93210, "url": "http://patchwork.ozlabs.org/api/1.2/people/93210/?format=api", "name": "Jonathan Wakely via Sourceware Forge", "email": "forge-bot+redi@forge-stage.sourceware.org" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.12@forge-stage.sourceware.org/mbox/", "series": [ { "id": 500987, "url": "http://patchwork.ozlabs.org/api/1.2/series/500987/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=500987", "date": "2026-04-22T10:44:17", "name": "atomic wait/notify ABI stabilization", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/500987/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2226286/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2226286/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)", "sourceware.org; dmarc=none (p=none dis=none)\n header.from=forge-stage.sourceware.org", "sourceware.org;\n spf=pass smtp.mailfrom=forge-stage.sourceware.org", "server2.sourceware.org;\n arc=none smtp.remote-ip=38.145.34.39" ], "Received": [ "from vm01.sourceware.org (vm01.sourceware.org\n [IPv6:2620:52:6:3111::32])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g0xMD1JSwz1yD5\n\tfor <incoming@patchwork.ozlabs.org>; Wed, 22 Apr 2026 21:09:43 +1000 (AEST)", "from vm01.sourceware.org (localhost [127.0.0.1])\n\tby sourceware.org (Postfix) with ESMTP id 2027C4162866\n\tfor <incoming@patchwork.ozlabs.org>; Wed, 22 Apr 2026 11:09:42 +0000 (GMT)", "from forge-stage.sourceware.org (vm08.sourceware.org [38.145.34.39])\n by sourceware.org (Postfix) with ESMTPS id 1119940986D2\n for <gcc-patches@gcc.gnu.org>; Wed, 22 Apr 2026 10:46:09 +0000 (GMT)", "from forge-stage.sourceware.org (localhost [IPv6:::1])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange x25519 server-signature ECDSA (prime256v1) server-digest SHA256)\n (No client certificate requested)\n by forge-stage.sourceware.org (Postfix) with ESMTPS id 262A242BBB\n for <gcc-patches@gcc.gnu.org>; Wed, 22 Apr 2026 10:46:02 +0000 (UTC)" ], "DKIM-Filter": [ "OpenDKIM Filter v2.11.0 sourceware.org 2027C4162866", "OpenDKIM Filter v2.11.0 sourceware.org 1119940986D2" ], "DMARC-Filter": "OpenDMARC Filter v1.4.2 sourceware.org 1119940986D2", "ARC-Filter": "OpenARC Filter v1.0.0 sourceware.org 1119940986D2", "ARC-Seal": "i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1776854769; cv=none;\n b=vN0PsnBr0QyzYVArMrjKxmrs4P4OzcUi8m7dO2DypXK+z0aRxbnpS/RZnYI3iqxj35/QyffY50MTg3i50rfUwHP7J5wBFR3xlv6EjlOVJrnMXN4WoPErXUD4BqtpAwI9pLpXY8g/xXIM9ajrmpX5Y8QJJawV3P2t0CLLaNLgTcw=", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1776854769; c=relaxed/simple;\n bh=WydmmoPvT9WAm9Oo/rymHl+IBAshWxr0cQw4NzS6OEQ=;\n h=From:Date:Subject:To:Message-ID;\n b=xA/TbJmr8Gx35D/LtSQcWdIvbUS54VerjpWFSljHKJJHFmOtRv5itM4cHRT43vUha8H1FsZ63x69GQHmXlnfmkCtr1LgHqYbGefgtVVn8QEitnFGjI3/V83WGr5DoYJSHYGEbqw5KwlU6sQRJjFcdjJ33V77/O9Uu/OKzQRLnxY=", "ARC-Authentication-Results": "i=1; server2.sourceware.org", "From": "Jonathan Wakely via Sourceware Forge\n <forge-bot+redi@forge-stage.sourceware.org>", "Date": "Wed, 22 Apr 2026 10:44:27 +0000", "Subject": "[PATCH v1 12/16] libstdc++: Optimise std::latch::arrive_and_wait", "To": "gcc-patches mailing list <gcc-patches@gcc.gnu.org>", "Message-ID": "\n <bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.12@forge-stage.sourceware.org>", "X-Mailer": "batrachomyomachia", "X-Pull-Request-Organization": "gcc", "X-Pull-Request-Repository": "gcc-TEST", "X-Pull-Request": "https://forge.sourceware.org/gcc/gcc-TEST/pulls/31", "References": "\n <bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.0@forge-stage.sourceware.org>", "In-Reply-To": "\n <bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.0@forge-stage.sourceware.org>", "X-Patch-URL": "\n https://forge.sourceware.org/redi/gcc/commit/26f3d12d57c02ae4771c946d0734fefebba3ecc1", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Reply-To": "gcc-patches mailing list <gcc-patches@gcc.gnu.org>, redi@gcc.gnu.org", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "From: Jonathan Wakely <jwakely@redhat.com>\n\nWe don't need to wait if we know the counter has reached zero.\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/std/latch (latch::arrive_and_wait): Optimise.\n---\n libstdc++-v3/include/std/latch | 17 +++++++++++++++--\n 1 file changed, 15 insertions(+), 2 deletions(-)", "diff": "diff --git a/libstdc++-v3/include/std/latch b/libstdc++-v3/include/std/latch\nindex 0a5bb0fdc6c4..f0e9850730ce 100644\n--- a/libstdc++-v3/include/std/latch\n+++ b/libstdc++-v3/include/std/latch\n@@ -101,8 +101,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n _GLIBCXX_ALWAYS_INLINE void\n arrive_and_wait(ptrdiff_t __update = 1) noexcept\n {\n- count_down(__update);\n- wait();\n+ // The standard specifies this functions as count_down(update); wait();\n+ // but we combine those two calls into one and avoid the wait() if we\n+ // know the counter reached zero.\n+\n+ __glibcxx_assert(__update >= 0 && __update <= max());\n+ // Use acq_rel here because an omitted wait() would have used acquire:\n+ auto const __old = __atomic_impl::fetch_sub(&_M_a, __update,\n+\t\t\t\t\t\t memory_order::acq_rel);\n+ if (std::cmp_equal(__old, __update))\n+\t__atomic_impl::notify_all(&_M_a);\n+ else\n+\t{\n+\t __glibcxx_assert(std::cmp_less(__update, __old));\n+\t wait();\n+\t}\n }\n \n private:\n", "prefixes": [ "v1", "12/16" ] }