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

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merged 1 commit into from
Jul 11, 2025
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[libc++][NFC] atomic::wait use public API on macOS #147146

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17 changes: 6 additions & 11 deletions libcxx/src/atomic.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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);
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Shouldn't this be calling os_sync_wake_by_address_any if __notify_one is set?

}

#elif defined(__FreeBSD__) && __SIZEOF_LONG__ == 8
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