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
