On 21/04/21 13:12 +0100, Jonathan Wakely wrote:
On 21/04/21 12:38 +0100, Jonathan Wakely wrote:
On 20/04/21 22:12 -0700, Thomas Rodgers wrote:
@@ -86,6 +88,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
}
+ _GLIBCXX_ALWAYS_INLINE bool
+ _M_try_acquire() noexcept
+ {
+ for (;;)
+ {
+ auto __err = sem_trywait(&_M_semaphore);
+ if (__err && (errno == EINTR))
+ continue;
+ else if (__err && (errno == EAGAIN))
+ return false;
+ else if (__err)
+ std::terminate();
+ else
+ break;
+ }
+ return true;
+ }
+
_GLIBCXX_ALWAYS_INLINE void
_M_release(std::ptrdiff_t __update) noexcept
{
Please just commit this part to trunk and gcc-11, not the macro
renaming (as that's been fixed by Jakub already).
I think on trunk I'd prefer to do the attached. WDYT?
In fact I think something like this is neded even on gcc-11 branch,
otherwise anything that tries to include <semaphore> without atomics
or sem_t gets hard errors:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100179
And <thread> includes <stop_token> which includes <semaphore>, meaning
<thread> is unusable on those targets.
So I think removing this #error is essential:
-// Note: the _GLIBCXX_REQUIRE_POSIX_SEMAPHORE macro can be used to force the
-// use of Posix semaphores (sem_t). Doing so however, alters the ABI.
-#if defined __cpp_lib_atomic_wait && !_GLIBCXX_REQUIRE_POSIX_SEMAPHORE
using __semaphore_impl = __atomic_semaphore;
-#elif _GLIBCXX_HAVE_POSIX_SEMAPHORE
- using __semaphore_impl = __platform_semaphore;
-#else
-# error "No suitable semaphore implementation available"
-#endif
+#endif // __cpp_lib_atomic_wait
