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GET /api/1.2/patches/2226309/?format=api
{ "id": 2226309, "url": "http://patchwork.ozlabs.org/api/1.2/patches/2226309/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.16@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.31.1.16@forge-stage.sourceware.org>", "list_archive_url": null, "date": "2026-04-22T10:44:31", "name": "[v1,16/16] libstdc++: Define __wait_result_type for atomic waiting", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "1f16efbe5b7ecd2aa5d84b358909fc38e7555ce8", "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.31.1.16@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/2226309/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2226309/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=38.145.34.32; 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 [38.145.34.32])\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 4g0xhs3jP5z1yD5\n\tfor <incoming@patchwork.ozlabs.org>; Wed, 22 Apr 2026 21:25:01 +1000 (AEST)", "from vm01.sourceware.org (localhost [127.0.0.1])\n\tby sourceware.org (Postfix) with ESMTP id 86A82409599B\n\tfor <incoming@patchwork.ozlabs.org>; Wed, 22 Apr 2026 11:24:59 +0000 (GMT)", "from forge-stage.sourceware.org (vm08.sourceware.org [38.145.34.39])\n by sourceware.org (Postfix) with ESMTPS id 8AA204015E81\n for <gcc-patches@gcc.gnu.org>; Wed, 22 Apr 2026 10:46:12 +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 5D72E42BBF\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 86A82409599B", "OpenDKIM Filter v2.11.0 sourceware.org 8AA204015E81" ], "DMARC-Filter": "OpenDMARC Filter v1.4.2 sourceware.org 8AA204015E81", "ARC-Filter": "OpenARC Filter v1.0.0 sourceware.org 8AA204015E81", "ARC-Seal": "i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1776854772; cv=none;\n b=u16f5oiHIDFzE2FhODmhF6FmexJQ0MH92lEWWIOELm/R3FQEzRg0NfLUPABV4LiLUzyacFXw86UGCdu0rIwGwmpT3d4yKUNleczEQuUoYui/FgujQ3OyEq/UOZGBAAcKishEgpOhawaOVabX9rSc2p9F7/JWOdUoEh/8xB+uG3M=", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1776854772; c=relaxed/simple;\n bh=AEj7V8TY/Vk8MsmXvPqO0MOv/0/DHWY8MUCYfODS9hk=;\n h=From:Date:Subject:To:Message-ID;\n b=OIHD4Euf+Q4Fc9aO1XtAizVysIfqnQe8fpVB5RKiqvrWgoqo2LduBUdk77H7oLHhhHKmZ4ANWPsmY0ksUq59lPYLxriEx63pIn6fzF7hY1kkGYaxfcMM3gFM1OzoB7b6UgSj/vEwwtlbdlcDiXVTRy3dyA7TFQKRE74BEIMHPio=", "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 10:44:31 +0000", "Subject": "[PATCH v1 16/16] libstdc++: Define __wait_result_type for atomic\n waiting", "To": "gcc-patches mailing list <gcc-patches@gcc.gnu.org>", "Message-ID": "\n <bmm.hhubrmqub2.gcc.gcc-TEST.redi.31.1.16@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/2ecceadcbe231874053dc40943a112aad0778d82", "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\nlibstdc++-v3/ChangeLog:\n\n\t* include/bits/atomic_timed_wait.h: Use __wait_result_type.\n\t* include/bits/atomic_wait.h (__wait_result_type): New struct.\n\t(__wait_args::_M_prep_for_wait_on): Rename to _M_setup_wait, use\n\t__wait_result_type.\n\t(__atomic_wait_address): Adjust to call _M_setup_wait.\n\t* src/c++20/atomic.cc (__spin_impl): Use __wait_result_type.\n\t(__wait_impl): Likewise.\n\t(__spin_until_impl): Likewise.\n\t(__wait_until_impl): Likewise.\n---\n libstdc++-v3/include/bits/atomic_timed_wait.h | 25 ++++-----\n libstdc++-v3/include/bits/atomic_wait.h | 48 +++++++++++-----\n libstdc++-v3/src/c++20/atomic.cc | 55 ++++++++++++-------\n 3 files changed, 80 insertions(+), 48 deletions(-)", "diff": "diff --git a/libstdc++-v3/include/bits/atomic_timed_wait.h b/libstdc++-v3/include/bits/atomic_timed_wait.h\nindex 3e25607b7d4c..230afbc96e7d 100644\n--- a/libstdc++-v3/include/bits/atomic_timed_wait.h\n+++ b/libstdc++-v3/include/bits/atomic_timed_wait.h\n@@ -98,18 +98,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \t\t\t\t\t\t __at.time_since_epoch());\n \n \tif constexpr (!is_same_v<__wait_clock_t, _Clock>)\n-\t if (!__res.first)\n+\t if (__res._M_timeout)\n \t {\n \t // We got a timeout when measured against __clock_t but\n \t // we need to check against the caller-supplied clock\n \t // to tell whether we should return a timeout.\n \t if (_Clock::now() < __atime)\n-\t\t__res.first = true;\n+\t\t__res._M_timeout = false;\n \t }\n \treturn __res;\n }\n \n- // Returns {true, val} if wait ended before a timeout.\n template<typename _Rep, typename _Period>\n __wait_result_type\n __wait_for(const void* __addr, __wait_args_base& __args,\n@@ -139,14 +138,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \t\t\t\tbool __bare_wait = false) noexcept\n {\n __detail::__wait_args __args{ __addr, __bare_wait };\n- _Tp __val = __args._M_prep_for_wait_on(__addr, __vfn);\n+ _Tp __val = __args._M_setup_wait(__addr, __vfn);\n while (!__pred(__val))\n \t{\n \t auto __res = __detail::__wait_until(__addr, __args, __atime);\n-\t if (!__res.first)\n-\t // timed out\n-\t return __res.first; // C++26 will also return last observed __val\n-\t __val = __args._M_prep_for_wait_on(__addr, __vfn);\n+\t if (__res._M_timeout)\n+\t return false; // C++26 will also return last observed __val\n+\t __val = __args._M_setup_wait(__addr, __vfn, __res);\n \t}\n return true; // C++26 will also return last observed __val\n }\n@@ -189,14 +187,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \t\t\t bool __bare_wait = false) noexcept\n {\n __detail::__wait_args __args{ __addr, __bare_wait };\n- _Tp __val = __args._M_prep_for_wait_on(__addr, __vfn);\n+ _Tp __val = __args._M_setup_wait(__addr, __vfn);\n while (!__pred(__val))\n \t{\n \t auto __res = __detail::__wait_for(__addr, __args, __rtime);\n-\t if (!__res.first)\n-\t // timed out\n-\t return __res.first; // C++26 will also return last observed __val\n-\t __val = __args._M_prep_for_wait_on(__addr, __vfn);\n+\t if (__res._M_timeout)\n+\t return false; // C++26 will also return last observed __val\n+\t __val = __args._M_setup_wait(__addr, __vfn);\n \t}\n return true; // C++26 will also return last observed __val\n }\n@@ -211,7 +208,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n {\n __detail::__wait_args __args{ __addr, __old, __order, __bare_wait };\n auto __res = __detail::__wait_for(__addr, __args, __rtime);\n- return __res.first; // C++26 will also return last observed __Val\n+ return !__res._M_timeout; // C++26 will also return last observed __val\n }\n \n template<typename _Tp, typename _ValFn,\ndiff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h\nindex 33e8d3202566..815726c16ccb 100644\n--- a/libstdc++-v3/include/bits/atomic_wait.h\n+++ b/libstdc++-v3/include/bits/atomic_wait.h\n@@ -105,6 +105,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \treturn __builtin_memcmp(&__a, &__b, sizeof(_Tp)) == 0;\n }\n \n+ // lightweight std::optional<__platform_wait_t>\n+ struct __wait_result_type\n+ {\n+ __platform_wait_t _M_val;\n+ unsigned char _M_has_val : 1; // _M_val value was loaded before return.\n+ unsigned char _M_timeout : 1; // Waiting function ended with timeout.\n+ unsigned char _M_unused : 6; // padding\n+ };\n+\n enum class __wait_flags : __UINT_LEAST32_TYPE__\n {\n __abi_version = 0,\n@@ -166,21 +175,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n template<typename _ValFn,\n \t typename _Tp = decay_t<decltype(std::declval<_ValFn&>()())>>\n \t_Tp\n-\t_M_prep_for_wait_on(const void* __addr, _ValFn __vfn)\n+\t_M_setup_wait(const void* __addr, _ValFn __vfn,\n+\t\t __wait_result_type __res = {})\n \t{\n \t if constexpr (__platform_wait_uses_type<_Tp>)\n \t {\n-\t _Tp __val = __vfn();\n-\t // If the wait is not proxied, set the value that we're waiting\n-\t // to change.\n-\t _M_old = __builtin_bit_cast(__platform_wait_t, __val);\n-\t return __val;\n+\t // If the wait is not proxied, the value we check when waiting\n+\t // is the value of the atomic variable itself.\n+\n+\t if (__res._M_has_val) // The previous wait loaded a recent value.\n+\t\t{\n+\t\t _M_old = __res._M_val;\n+\t\t return __builtin_bit_cast(_Tp, __res._M_val);\n+\t\t}\n+\t else // Load the value from __vfn\n+\t\t{\n+\t\t _Tp __val = __vfn();\n+\t\t _M_old = __builtin_bit_cast(__platform_wait_t, __val);\n+\t\t return __val;\n+\t\t}\n \t }\n-\t else\n+\t else // It's a proxy wait and the proxy's _M_ver is used.\n \t {\n-\t // Otherwise, it's a proxy wait and the proxy's _M_ver is used.\n-\t // This load must happen before the one done by __vfn().\n-\t _M_load_proxy_wait_val(__addr);\n+\t if (__res._M_has_val) // The previous wait loaded a recent value.\n+\t\t_M_old = __res._M_val;\n+\t else // Load _M_ver from the proxy (must happen before __vfn()).\n+\t\t_M_load_proxy_wait_val(__addr);\n \t return __vfn();\n \t }\n \t}\n@@ -204,8 +224,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \t}\n };\n \n- using __wait_result_type = pair<bool, __platform_wait_t>;\n-\n __wait_result_type\n __wait_impl(const void* __addr, __wait_args_base&);\n \n@@ -222,11 +240,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n \t\t\t bool __bare_wait = false) noexcept\n {\n __detail::__wait_args __args{ __addr, __bare_wait };\n- _Tp __val = __args._M_prep_for_wait_on(__addr, __vfn);\n+ _Tp __val = __args._M_setup_wait(__addr, __vfn);\n while (!__pred(__val))\n \t{\n-\t __detail::__wait_impl(__addr, __args);\n-\t __val = __args._M_prep_for_wait_on(__addr, __vfn);\n+\t auto __res = __detail::__wait_impl(__addr, __args);\n+\t __val = __args._M_setup_wait(__addr, __vfn, __res);\n \t}\n // C++26 will return __val\n }\ndiff --git a/libstdc++-v3/src/c++20/atomic.cc b/libstdc++-v3/src/c++20/atomic.cc\nindex b9ad66b1ec30..a3ec92a10d56 100644\n--- a/libstdc++-v3/src/c++20/atomic.cc\n+++ b/libstdc++-v3/src/c++20/atomic.cc\n@@ -48,6 +48,8 @@\n # endif\n #endif\n \n+#pragma GCC diagnostic ignored \"-Wmissing-field-initializers\"\n+\n namespace std\n {\n _GLIBCXX_BEGIN_NAMESPACE_VERSION\n@@ -208,21 +210,23 @@ namespace\n constexpr auto __atomic_spin_count_relax = 12;\n constexpr auto __atomic_spin_count = 16;\n \n+ // This function always returns _M_has_val == true and _M_val == *__addr.\n+ // _M_timeout == (*__addr == __args._M_old).\n __wait_result_type\n __spin_impl(const __platform_wait_t* __addr, const __wait_args_base& __args)\n {\n- __platform_wait_t __val;\n+ __platform_wait_t __val{};\n for (auto __i = 0; __i < __atomic_spin_count; ++__i)\n {\n \t__atomic_load(__addr, &__val, __args._M_order);\n \tif (__val != __args._M_old)\n-\t return { true, __val };\n+\t return { ._M_val = __val, ._M_has_val = true, ._M_timeout = false };\n \tif (__i < __atomic_spin_count_relax)\n \t __thread_relax();\n \telse\n \t __thread_yield();\n }\n- return { false, __val };\n+ return { ._M_val = __val, ._M_has_val = true, ._M_timeout = true };\n }\n \n inline __waitable_state*\n@@ -263,7 +267,7 @@ __wait_impl(const void* __addr, __wait_args_base& __args)\n if (__args & __wait_flags::__do_spin)\n {\n auto __res = __detail::__spin_impl(__wait_addr, __args);\n- if (__res.first)\n+ if (!__res._M_timeout)\n \treturn __res;\n if (__args & __wait_flags::__spin_only)\n \treturn __res;\n@@ -271,17 +275,21 @@ __wait_impl(const void* __addr, __wait_args_base& __args)\n \n #ifdef _GLIBCXX_HAVE_PLATFORM_WAIT\n if (__args & __wait_flags::__track_contention)\n- set_wait_state(__addr, __args);\n+ set_wait_state(__addr, __args); // scoped_wait needs a __waitable_state\n scoped_wait s(__args);\n __platform_wait(__wait_addr, __args._M_old);\n- return { false, __args._M_old };\n+ // We haven't loaded a new value so return false as first member:\n+ return { ._M_val = __args._M_old, ._M_has_val = false, ._M_timeout = false };\n #else\n waiter_lock l(__args);\n __platform_wait_t __val;\n __atomic_load(__wait_addr, &__val, __args._M_order);\n if (__val == __args._M_old)\n- __state->_M_cv.wait(__state->_M_mtx);\n- return { false, __val };\n+ {\n+ __state->_M_cv.wait(__state->_M_mtx);\n+ return { ._M_val = __val, ._M_has_val = false, ._M_timeout = false };\n+ }\n+ return { ._M_val = __val, ._M_has_val = true, ._M_timeout = false };\n #endif\n }\n \n@@ -389,6 +397,7 @@ __cond_wait_until(__condvar& __cv, mutex& __mx,\n }\n #endif // ! HAVE_PLATFORM_TIMED_WAIT\n \n+// Like __spin_impl, always returns _M_has_val == true.\n __wait_result_type\n __spin_until_impl(const __platform_wait_t* __addr,\n \t\t const __wait_args_base& __args,\n@@ -411,14 +420,18 @@ __spin_until_impl(const __platform_wait_t* __addr,\n #endif\n if (__elapsed > 4us)\n \t__thread_yield();\n- else if (auto __res = __detail::__spin_impl(__addr, __args); __res.first)\n-\treturn __res;\n+ else\n+\t{\n+\t auto __res = __detail::__spin_impl(__addr, __args);\n+\t if (!__res._M_timeout)\n+\t return __res;\n+\t}\n \n __atomic_load(__addr, &__val, __args._M_order);\n if (__val != __args._M_old)\n-\treturn { true, __val };\n+\treturn { ._M_val = __val, ._M_has_val = true, ._M_timeout = false };\n }\n- return { false, __val };\n+ return { ._M_val = __val, ._M_has_val = true, ._M_timeout = true };\n }\n } // namespace\n \n@@ -437,7 +450,7 @@ __wait_until_impl(const void* __addr, __wait_args_base& __args,\n if (__args & __wait_flags::__do_spin)\n {\n auto __res = __detail::__spin_until_impl(__wait_addr, __args, __atime);\n- if (__res.first)\n+ if (!__res._M_timeout)\n \treturn __res;\n if (__args & __wait_flags::__spin_only)\n \treturn __res;\n@@ -448,17 +461,21 @@ __wait_until_impl(const void* __addr, __wait_args_base& __args,\n set_wait_state(__addr, __args);\n scoped_wait s(__args);\n if (__platform_wait_until(__wait_addr, __args._M_old, __atime))\n- return { true, __args._M_old };\n+ return { ._M_val = __args._M_old, ._M_has_val = false, ._M_timeout = false };\n else\n- return { false, __args._M_old };\n+ return { ._M_val = __args._M_old, ._M_has_val = false, ._M_timeout = true };\n #else\n waiter_lock l(__args);\n __platform_wait_t __val;\n __atomic_load(__wait_addr, &__val, __args._M_order);\n- if (__val == __args._M_old\n-\t&& __cond_wait_until(__state->_M_cv, __state->_M_mtx, __atime))\n- return { true, __val };\n- return { false, __val };\n+ if (__val == __args._M_old)\n+ {\n+ if (__cond_wait_until(__state->_M_cv, __state->_M_mtx, __atime))\n+\treturn { ._M_val = __val, ._M_has_val = false, ._M_timeout = false };\n+ else\n+\treturn { ._M_val = __val, ._M_has_val = false, ._M_timeout = true };\n+ }\n+ return { ._M_val = __val, ._M_has_val = true, ._M_timeout = false };\n #endif\n }\n \n", "prefixes": [ "v1", "16/16" ] }