[libc++][NFC] atomic::wait use public API on macOS #147146

huixie90 · 2025-07-05T13:28:44Z

At the moment, we use the os internal functions __ulock_wait. This patch updates the code on macOS to use the public API os_sync_wait_on_address.

Fixes #146142

llvmbot · 2025-07-05T13:29:14Z

@llvm/pr-subscribers-libcxx

Author: Hui (huixie90)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/147146.diff

1 Files Affected:

(modified) libcxx/src/atomic.cpp (+6-11)

diff --git a/libcxx/src/atomic.cpp b/libcxx/src/atomic.cpp
index c1af8d6f95aae..6cb02550be2f7 100644
--- a/libcxx/src/atomic.cpp
+++ b/libcxx/src/atomic.cpp
@@ -41,6 +41,10 @@
 // OpenBSD has no indirect syscalls
 #  define _LIBCPP_FUTEX(...) futex(__VA_ARGS__)
 
+#elif defined(__APPLE__) && defined(_LIBCPP_USE_ULOCK)
+
+#  include <os/os_sync_wait_on_address.h>
+
 #else // <- Add other operating systems here
 
 // Baseline needs no new headers
@@ -65,24 +69,15 @@ static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const vo
 
 #elif defined(__APPLE__) && defined(_LIBCPP_USE_ULOCK)
 
-extern "C" int __ulock_wait(
-    uint32_t operation, void* addr, uint64_t value, uint32_t timeout); /* timeout is specified in microseconds */
-extern "C" int __ulock_wake(uint32_t operation, void* addr, uint64_t wake_value);
-
-// https://github.com/apple/darwin-xnu/blob/2ff845c2e033bd0ff64b5b6aa6063a1f8f65aa32/bsd/sys/ulock.h#L82
-#  define UL_COMPARE_AND_WAIT64 5
-#  define ULF_WAKE_ALL 0x00000100
-
 static void
 __libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __ptr, __cxx_contention_t __val) {
   static_assert(sizeof(__cxx_atomic_contention_t) == 8, "Waiting on 8 bytes value");
-  __ulock_wait(UL_COMPARE_AND_WAIT64, const_cast<__cxx_atomic_contention_t*>(__ptr), __val, 0);
+  os_sync_wait_on_address(const_cast<__cxx_atomic_contention_t*>(__ptr), __val, 8, OS_SYNC_WAIT_ON_ADDRESS_NONE);
 }
 
 static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const volatile* __ptr, bool __notify_one) {
   static_assert(sizeof(__cxx_atomic_contention_t) == 8, "Waking up on 8 bytes value");
-  __ulock_wake(
-      UL_COMPARE_AND_WAIT64 | (__notify_one ? 0 : ULF_WAKE_ALL), const_cast<__cxx_atomic_contention_t*>(__ptr), 0);
+  os_sync_wake_by_address_all(const_cast<__cxx_atomic_contention_t*>(__ptr), 8, OS_SYNC_WAKE_BY_ADDRESS_NONE);
 }
 
 #elif defined(__FreeBSD__) && __SIZEOF_LONG__ == 8

ldionne

Thanks for the cleanup, this is great!

JDevlieghere · 2025-07-11T23:21:44Z

This is causing a build failure on Darwin: https://ci.swift.org/view/all/job/llvm.org/view/LLDB/job/as-lldb-cmake/

[2025-07-11T23:04:47.605Z] /Users/ec2-user/jenkins/workspace/llvm.org/as-lldb-cmake/llvm-project/libcxx/src/atomic.cpp:46:12: fatal error: 'os/os_sync_wait_on_address.h' file not found
[2025-07-11T23:04:47.605Z]    46 | #  include <os/os_sync_wait_on_address.h>
[2025-07-11T23:04:47.605Z]       |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[2025-07-11T23:04:47.605Z] 1 error generated.
[2025-07-11T23:04:47.605Z] [25/486] Building CXX object libcxx/src/CMakeFiles/cxx_static.dir/atomic.cpp.o

This reverts commit b9d8d1e.

Reverts #147146 This is failing to build on our public macOS CI: https://green.lab.llvm.org/job/llvm.org/view/LLDB/job/lldb-cmake-sanitized/ ``` 06:48:56 FAILED: libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o 06:48:56 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/bin/clang++ --target=arm64-apple-darwin23.1.0 -DLIBCXX_BUILDING_LIBCXXABI -DLIBC_NAMESPACE=__llvm_libc_common_utils -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_LIBCPP_BUILDING_LIBRARY -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/include/c++/v1 -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxxabi/include -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/cmake/Modules/../../libc -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -O3 -DNDEBUG -std=c++23 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -mmacosx-version-min=14.1 -fPIC -UNDEBUG -faligned-allocation -nostdinc++ -fvisibility-inlines-hidden -fvisibility=hidden -fsized-deallocation -Wall -Wextra -Wnewline-eof -Wshadow -Wwrite-strings -Wno-unused-parameter -Wno-long-long -Werror=return-type -Wextra-semi -Wundef -Wunused-template -Wformat-nonliteral -Wzero-length-array -Wdeprecated-redundant-constexpr-static-def -Wno-nullability-completeness -Wno-user-defined-literals -Wno-covered-switch-default -Wno-suggest-override -Wno-error -fdebug-prefix-map=/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/include/c++/v1=/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/include -MD -MT libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o -MF libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o.d -o libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o -c /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src/atomic.cpp 06:48:56 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src/atomic.cpp:46:12: fatal error: 'os/os_sync_wait_on_address.h' file not found 06:48:56 46 | # include <os/os_sync_wait_on_address.h> 06:48:56 | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 06:48:56 1 error generated. ``` This is the configuration the failing bots are running: ``` 06:25:12 + sw_vers 06:25:12 ProductName: macOS 06:25:12 ProductVersion: 14.1 06:25:12 BuildVersion: 23B74 06:25:12 + xcodebuild -version 06:25:12 Xcode 15.2 06:25:12 Build version 15C5500c ``` The Intel bots are building fine though. Probably because they're on a newer OS where the headers are available? ``` 10:03:35 + sw_vers 10:03:35 ProductName: macOS 10:03:35 ProductVersion: 15.1.1 10:03:35 BuildVersion: 24B91 10:03:35 + xcodebuild -version 10:03:39 Xcode 16.2 10:03:39 Build version 16C5031c 10:03:39 + cmake --version 10:03:39 cmake version 3.30.2 ```

…" (#148705) Reverts llvm/llvm-project#147146 This is failing to build on our public macOS CI: https://green.lab.llvm.org/job/llvm.org/view/LLDB/job/lldb-cmake-sanitized/ ``` 06:48:56 FAILED: libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o 06:48:56 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/bin/clang++ --target=arm64-apple-darwin23.1.0 -DLIBCXX_BUILDING_LIBCXXABI -DLIBC_NAMESPACE=__llvm_libc_common_utils -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_LIBCPP_BUILDING_LIBRARY -D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/include/c++/v1 -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxxabi/include -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/cmake/Modules/../../libc -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -O3 -DNDEBUG -std=c++23 -isysroot /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk -mmacosx-version-min=14.1 -fPIC -UNDEBUG -faligned-allocation -nostdinc++ -fvisibility-inlines-hidden -fvisibility=hidden -fsized-deallocation -Wall -Wextra -Wnewline-eof -Wshadow -Wwrite-strings -Wno-unused-parameter -Wno-long-long -Werror=return-type -Wextra-semi -Wundef -Wunused-template -Wformat-nonliteral -Wzero-length-array -Wdeprecated-redundant-constexpr-static-def -Wno-nullability-completeness -Wno-user-defined-literals -Wno-covered-switch-default -Wno-suggest-override -Wno-error -fdebug-prefix-map=/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/lldb-build/include/c++/v1=/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/include -MD -MT libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o -MF libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o.d -o libcxx/src/CMakeFiles/cxx_shared.dir/atomic.cpp.o -c /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src/atomic.cpp 06:48:56 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-sanitized/llvm-project/libcxx/src/atomic.cpp:46:12: fatal error: 'os/os_sync_wait_on_address.h' file not found 06:48:56 46 | # include <os/os_sync_wait_on_address.h> 06:48:56 | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 06:48:56 1 error generated. ``` This is the configuration the failing bots are running: ``` 06:25:12 + sw_vers 06:25:12 ProductName: macOS 06:25:12 ProductVersion: 14.1 06:25:12 BuildVersion: 23B74 06:25:12 + xcodebuild -version 06:25:12 Xcode 15.2 06:25:12 Build version 15C5500c ``` The Intel bots are building fine though. Probably because they're on a newer OS where the headers are available? ``` 10:03:35 + sw_vers 10:03:35 ProductName: macOS 10:03:35 ProductVersion: 15.1.1 10:03:35 BuildVersion: 24B91 10:03:35 + xcodebuild -version 10:03:39 Xcode 16.2 10:03:39 Build version 16C5031c 10:03:39 + cmake --version 10:03:39 cmake version 3.30.2 ```

aharrison24 · 2025-08-20T21:57:53Z

libcxx/src/atomic.cpp

  static_assert(sizeof(__cxx_atomic_contention_t) == 8, "Waking up on 8 bytes value");
-  __ulock_wake(
-      UL_COMPARE_AND_WAIT64 | (__notify_one ? 0 : ULF_WAKE_ALL), const_cast<__cxx_atomic_contention_t*>(__ptr), 0);
+  os_sync_wake_by_address_all(const_cast<__cxx_atomic_contention_t*>(__ptr), 8, OS_SYNC_WAKE_BY_ADDRESS_NONE);


Shouldn't this be calling os_sync_wake_by_address_any if __notify_one is set?

[libc++][NFC] atomic::wait use public API on macOS

ff63365

huixie90 requested a review from a team as a code owner July 5, 2025 13:28

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Jul 5, 2025

ldionne approved these changes Jul 7, 2025

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ldionne merged commit b9d8d1e into llvm:main Jul 11, 2025
76 of 79 checks passed

Michael137 added a commit that referenced this pull request Jul 14, 2025

Revert "[libc++][NFC] atomic::wait use public API on macOS (#147146)"

33fc0ae

This reverts commit b9d8d1e.

Michael137 mentioned this pull request Jul 14, 2025

Revert "[libc++][NFC] atomic::wait use public API on macOS" #148705

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aharrison24 reviewed Aug 20, 2025

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