{"id":2225760,"url":"http://patchwork.ozlabs.org/api/patches/2225760/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260421144257.1000552-1-jwakely@redhat.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/projects/17/?format=json","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":"<20260421144257.1000552-1-jwakely@redhat.com>","list_archive_url":null,"date":"2026-04-21T14:42:18","name":"libstdc++: Add platform wait functions for Darwin [PR120527]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"99ecdae2154587c7600880fb32c3976cadad7572","submitter":{"id":48004,"url":"http://patchwork.ozlabs.org/api/people/48004/?format=json","name":"Jonathan Wakely","email":"jwakely@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260421144257.1000552-1-jwakely@redhat.com/mbox/","series":[{"id":500827,"url":"http://patchwork.ozlabs.org/api/series/500827/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=500827","date":"2026-04-21T14:42:18","name":"libstdc++: Add platform wait functions for Darwin [PR120527]","version":1,"mbox":"http://patchwork.ozlabs.org/series/500827/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2225760/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2225760/checks/","tags":{},"related":[],"headers":{"Return-Path":"","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\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com 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","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"Darwin has kernel support for this facility from 10.12 (macOS Sierra).\n\nFrom 10.15 (macOS Catalina) 64bit qualitities are supported.\n\nWhen the library is built for 10.12+ both 32b and 64b quantities will be\nsupported by the DSO which means it can be installed on 10.12+ with support\nfor 64bit available when the instalation is >= 10.15.\n\nThe header will only recognise 64b quantities when the deployment version\nis >= 10.15.\n\nIf the library is built for <= 10.11, the support will be missing and attempts\nto use it wlll result in link errors.\n\nThe platform wait type is unconditionally set to 32bits, since this is compatible\nacross supported OS editions.\n\n\tPR libstdc++/120527\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/bits/atomic_wait.h:\n\t* src/c++20/atomic.cc (__ulock_wait): Enable supported Darwin versions.\n\t(__ulock_wake): Likewise.\n\t(UL_COMPARE_AND_WAIT): New.\n\t(UL_COMPARE_AND_WAIT64): New.\n\t(ULF_WAKE_ALL): New.\n\t(_GLIBCXX_HAVE_PLATFORM_WAIT): Enable for suppported Darwin versions.\n\nCo-authored-by: Iain Sandoe \nSigned-off-by: Iain Sandoe \n---\n\nTested x86_64-linux and various darwin systems (by Iain).\n\nPushed to trunk.\n\n libstdc++-v3/include/bits/atomic_wait.h | 21 +++++++\n libstdc++-v3/src/c++20/atomic.cc | 74 +++++++++++++++++++++++++\n 2 files changed, 95 insertions(+)","diff":"diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h\nindex 47bd1073f881..704c10d5f382 100644\n--- a/libstdc++-v3/include/bits/atomic_wait.h\n+++ b/libstdc++-v3/include/bits/atomic_wait.h\n@@ -69,6 +69,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n inline constexpr bool __platform_wait_uses_type\n = __detail::__waitable<_Tp>\n \t && sizeof(_Tp) == sizeof(int) && alignof(_Tp) >= 4;\n+#elif defined __APPLE__ \\\n+ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101200\n+ namespace __detail\n+ {\n+ using __platform_wait_t = __INT32_TYPE__;\n+ inline constexpr size_t __platform_wait_alignment = 4;\n+ }\n+ // Defined to true for a subset of __waitable types which are statically\n+ // known to definitely be able to use __ulock_wait, not a proxy wait.\n+ // We know that OS Versions later than 10.15 support 64b wait types even\n+ // though we must make the __platform_wait_t 32b for compatibility with\n+ // earlier versions of __ulock_xxxx.\n+ template\n+ inline constexpr bool __platform_wait_uses_type\n+ = __detail::__waitable<_Tp>\n+# if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101500\n+\t && sizeof(_Tp) == 4 && alignof(_Tp) >= 4;\n+# else\n+\t && ((sizeof(_Tp) == 4 && alignof(_Tp) >= 4)\n+\t\t|| (sizeof(_Tp) == 8 && alignof(_Tp) >= 8));\n+# endif\n #elif defined __FreeBSD__ && __SIZEOF_LONG__ == 8\n namespace __detail\n {\ndiff --git a/libstdc++-v3/src/c++20/atomic.cc b/libstdc++-v3/src/c++20/atomic.cc\nindex 177c503330d5..3e02f437db3c 100644\n--- a/libstdc++-v3/src/c++20/atomic.cc\n+++ b/libstdc++-v3/src/c++20/atomic.cc\n@@ -27,6 +27,7 @@\n #if __glibcxx_atomic_wait\n #include \n #include \n+#include // cmp_less\n #include // uint32_t, uint64_t, uintptr_t\n #include // INT_MAX\n #include // errno, ETIMEDOUT, etc.\n@@ -39,6 +40,19 @@\n # include \n # include // timespec\n # define _GLIBCXX_HAVE_PLATFORM_WAIT 1\n+#elif defined __APPLE__ \\\n+ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101200\n+// These are thin wrappers over the underlying syscall, they exist on\n+// earlier versions of the OS, however those versions do not support the\n+// UL_COMPARE_AND_WAIT64 operation.\n+extern \"C\" int\n+__ulock_wait(uint32_t operation, void* addr, uint64_t value, uint32_t timeout);\n+extern \"C\" int\n+__ulock_wake(uint32_t operation, void* addr, uint64_t wake_value);\n+# define UL_COMPARE_AND_WAIT 1\n+# define UL_COMPARE_AND_WAIT64 5\n+# define ULF_WAKE_ALL 0x00000100\n+# define _GLIBCXX_HAVE_PLATFORM_WAIT 1\n #elif defined __FreeBSD__ && __FreeBSD__ >= 11 && __SIZEOF_LONG__ == 8\n # include \n # include \n@@ -154,6 +168,66 @@ namespace\n __platform_load(const int* addr, int order, int /* obj_sz */) noexcept\n { return __atomic_load_n(addr, order); }\n \n+#elif defined __APPLE__ \\\n+ && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101200\n+\n+ [[gnu::always_inline]]\n+ inline uint32_t\n+ wait_op(int obj_sz) noexcept\n+ {\n+ __glibcxx_assert(obj_sz == 4 || obj_sz == 8);\n+ return obj_sz == 4 ? UL_COMPARE_AND_WAIT : UL_COMPARE_AND_WAIT64;\n+ }\n+\n+ void\n+ __platform_wait(const void* addr, uint64_t val, int obj_sz) noexcept\n+ {\n+ if (0 > __ulock_wait(wait_op(obj_sz), const_cast(addr), val, 0))\n+ if (errno != EINTR && errno != EFAULT)\n+\t__throw_system_error(errno);\n+ }\n+\n+ void\n+ __platform_notify(const void* addr, bool all, int obj_sz) noexcept\n+ {\n+ uint32_t op = wait_op (obj_sz);\n+ if (all)\n+ op |= ULF_WAKE_ALL;\n+ __ulock_wake(op, const_cast(addr), 0);\n+ }\n+\n+ // returns true if wait ended before timeout\n+ bool\n+ __platform_wait_until(const void* addr, uint64_t val,\n+\t\t\tconst __wait_clock_t::time_point& atime,\n+\t\t\tint obj_sz) noexcept\n+ {\n+ auto reltime\n+ = chrono::ceil(atime - __wait_clock_t::now());\n+ if (reltime <= reltime.zero())\n+ return false;\n+ uint32_t timeout = numeric_limits::max();\n+ if (std::cmp_less(reltime.count(), timeout))\n+ timeout = reltime.count();\n+\n+ if (0 > __ulock_wait(wait_op(obj_sz), const_cast(addr), val,\n+\t\t\t timeout))\n+ {\n+\tif (errno == ETIMEDOUT)\n+\t return timeout == numeric_limits::max();\n+\tif (errno != EINTR && errno != EFAULT)\n+\t __throw_system_error(errno);\n+ }\n+ return true;\n+ }\n+\n+ // ??? CHECKME: this could likely be more efficient.\n+ [[gnu::always_inline]]\n+ inline __wait_value_type\n+ __platform_load(const __platform_wait_t* addr, int memory_order,\n+\t\t int /* obj_sz */) noexcept\n+ { return __atomic_load_n(addr, memory_order); }\n+\n #elif defined __FreeBSD__ && __SIZEOF_LONG__ == 8\n [[gnu::always_inline]]\n inline int\n","prefixes":[]}