On Tue, Nov 25, 2025 at 1:17 PM Jonathan Wakely <[email protected]> wrote:
>
> This defines __platform_wait, __platform_notify, and
> __platform_wait_until for darwin, making use of the futex syscall.
small typo there. s/darwin/openbsd/ :).
Thanks,
Andrew
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/120527
> * include/bits/atomic_wait.h [__OpenBSD__]: Reuse Linux
> definitions of __platform_wait_t and __platform_wait_uses_type.
> * src/c++20/atomic.cc [__OpenBSD__] (_GLIBCXX_HAVE_PLATFORM_WAIT)
> (__platform_wait, __platform_notify, __platform_wait_until):
> Define.
> ---
>
> Untested, so I don't plan to commit this.
>
> libstdc++-v3/include/bits/atomic_wait.h | 3 +-
> libstdc++-v3/src/c++20/atomic.cc | 40 +++++++++++++++++++++++++
> 2 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/include/bits/atomic_wait.h
> b/libstdc++-v3/include/bits/atomic_wait.h
> index af4b2ab46a04..22877ad46755 100644
> --- a/libstdc++-v3/include/bits/atomic_wait.h
> +++ b/libstdc++-v3/include/bits/atomic_wait.h
> @@ -55,7 +55,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> = is_scalar_v<_Tp> && (sizeof(_Tp) <= sizeof(__UINT64_TYPE__));
> }
>
> -#if defined _GLIBCXX_HAVE_LINUX_FUTEX || defined __DragonFly__
> +#if defined _GLIBCXX_HAVE_LINUX_FUTEX || defined __DragonFly__ \
> + || defined __OpenBSD__
> namespace __detail
> {
> // Use futex syscall on int objects.
> diff --git a/libstdc++-v3/src/c++20/atomic.cc
> b/libstdc++-v3/src/c++20/atomic.cc
> index 87a1e24d8980..a788000fab7b 100644
> --- a/libstdc++-v3/src/c++20/atomic.cc
> +++ b/libstdc++-v3/src/c++20/atomic.cc
> @@ -56,6 +56,10 @@ __ulock_wake(uint32_t operation, void* addr, uint64_t
> wake_value);
> #elif defined __DragonFly__
> # include <unistd.h>
> # define _GLIBCXX_HAVE_PLATFORM_WAIT 1
> +#elif defined __OpenBSD__
> +# include <sys/time.h>
> +# include <sys/futex.h>
> +# define _GLIBCXX_HAVE_PLATFORM_WAIT 1
> #endif
>
> #pragma GCC diagnostic ignored "-Wmissing-field-initializers"
> @@ -242,6 +246,42 @@ namespace
> }
> return true;
> }
> +#elif defined __OpenBSD__
> + void
> + __platform_wait(const void* addr, uint64_t val, int /* obj_sz */) noexcept
> + {
> + if (futex(static_cast<uint32_t*>(const_cast<void*>(addr)), FUTEX_WAIT,
> + (int)val, nullptr, nullptr))
> + if (errno == EAGAIN || errno == EINTR || errno == ECANCELED)
> + return;
> + __throw_system_error(errno);
> + }
> +
> + void
> + __platform_notify(const void* addr, bool all, int /* obj_sz */) noexcept
> + {
> + futex(static_cast<uint32_t*>(const_cast<void*>(addr)), FUTEX_WAKE,
> + all ? INT_MAX : 1, nullptr, nullptr);
> + }
> +
> + // returns true if wait ended before timeout
> + bool
> + __platform_wait_until(const void* addr, uint64_t val,
> + const __wait_clock_t::time_point& atime,
> + int /* obj_sz */) noexcept
> + {
> + struct timespec timeout = chrono::__to_timeout_timespec(atime);
> + if (futex(static_cast<uint32_t*>(const_cast<void*>(addr)), FUTEX_WAIT,
> + (int)val, &timeout, nullptr))
> + {
> + if (errno == ETIMEDOUT)
> + return false;
> + if (errno == EAGAIN || errno == EINTR || errno == ECANCELED)
> + return true;
> + __throw_system_error(errno);
> + }
> + return true;
> + }
> #endif // HAVE_LINUX_FUTEX
>
> // The state used by atomic waiting and notifying functions.
> --
> 2.51.1
>
