How about this? I don't think we should worry about targets without atomic int, so don't bother using types smaller than int.
-- >8 -- For non-futex targets the __platform_wait_t type is currently uint64_t, but that requires a lock in libatomic for some 32-bit targets. We don't really need a 64-bit type, so use unsigned long if that is lock-free, and int otherwise. This should mean it's lock-free on a wider set of targets. libstdc++-v3/ChangeLog: * include/bits/atomic_wait.h (__detail::__platform_wait_t): Define as unsigned long if always lock-free, and unsigned int otherwise. --- libstdc++-v3/include/bits/atomic_wait.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h index bd1ed56d157..46f39f10cbc 100644 --- a/libstdc++-v3/include/bits/atomic_wait.h +++ b/libstdc++-v3/include/bits/atomic_wait.h @@ -64,7 +64,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // and __platform_notify() if there is a more efficient primitive supported // by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than // a mutex/condvar based wait. - using __platform_wait_t = uint64_t; +# if ATOMIC_LONG_LOCK_FREE == 2 + using __platform_wait_t = unsigned long; +# else + using __platform_wait_t = unsigned int; +# endif inline constexpr size_t __platform_wait_alignment = __alignof__(__platform_wait_t); #endif -- 2.39.0