The __detail::__wait_until function has a comment that should have been
removed when r16-1000-g225622398a9631 changed the return type from a
std::pair to a struct with three members.
__atomic_wait_address_until_v returns __res.first which should have been
changed when __res was no longer a std::pair.
Fix _M_spin_until_impl so that the _M_has_val member of the result is
accurate. If the deadline has passed then it never enters the loop and
so never loads a fresh value, so _M_has_val should be false.
libstdc++-v3/ChangeLog:
* include/bits/atomic_timed_wait.h (__detail::__wait_until):
Remove incorrect comment.
(__atomic_wait_address_until_v): Fix return statement.
* src/c++20/atomic.cc (__spin_until_impl): Fix incorrect
return value. Reuse result of first call to clock.
---
Tested x86_64-linux.
libstdc++-v3/include/bits/atomic_timed_wait.h | 3 +--
libstdc++-v3/src/c++20/atomic.cc | 24 ++++++++++++-------
2 files changed, 16 insertions(+), 11 deletions(-)
diff --git a/libstdc++-v3/include/bits/atomic_timed_wait.h
b/libstdc++-v3/include/bits/atomic_timed_wait.h
index 230afbc96e7d..e22c13f47b18 100644
--- a/libstdc++-v3/include/bits/atomic_timed_wait.h
+++ b/libstdc++-v3/include/bits/atomic_timed_wait.h
@@ -87,7 +87,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__wait_until_impl(const void* __addr, __wait_args_base& __args,
const __wait_clock_t::duration& __atime);
- // Returns {true, val} if wait ended before a timeout.
template<typename _Clock, typename _Dur>
__wait_result_type
__wait_until(const void* __addr, __wait_args_base& __args,
@@ -159,7 +158,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
__detail::__wait_args __args{ __addr, __old, __order, __bare_wait };
auto __res = __detail::__wait_until(__addr, &__args, __atime);
- return __res.first; // C++26 will also return last observed __val
+ return !__res._M_timeout; // C++26 will also return last observed __val
}
template<typename _Tp, typename _ValFn,
diff --git a/libstdc++-v3/src/c++20/atomic.cc b/libstdc++-v3/src/c++20/atomic.cc
index a3ec92a10d56..4120e1a0817f 100644
--- a/libstdc++-v3/src/c++20/atomic.cc
+++ b/libstdc++-v3/src/c++20/atomic.cc
@@ -397,17 +397,18 @@ __cond_wait_until(__condvar& __cv, mutex& __mx,
}
#endif // ! HAVE_PLATFORM_TIMED_WAIT
-// Like __spin_impl, always returns _M_has_val == true.
+// Unlike __spin_impl, does not always return _M_has_val == true.
+// If the deadline has already passed then no fresh value is loaded.
__wait_result_type
__spin_until_impl(const __platform_wait_t* __addr,
const __wait_args_base& __args,
const __wait_clock_t::time_point& __deadline)
{
- auto __t0 = __wait_clock_t::now();
using namespace literals::chrono_literals;
- __platform_wait_t __val{};
- auto __now = __wait_clock_t::now();
+ __wait_result_type __res{};
+ auto __t0 = __wait_clock_t::now();
+ auto __now = __t0;
for (; __now < __deadline; __now = __wait_clock_t::now())
{
auto __elapsed = __now - __t0;
@@ -422,16 +423,21 @@ __spin_until_impl(const __platform_wait_t* __addr,
__thread_yield();
else
{
- auto __res = __detail::__spin_impl(__addr, __args);
+ __res = __detail::__spin_impl(__addr, __args);
if (!__res._M_timeout)
return __res;
}
- __atomic_load(__addr, &__val, __args._M_order);
- if (__val != __args._M_old)
- return { ._M_val = __val, ._M_has_val = true, ._M_timeout = false };
+ __atomic_load(__addr, &__res._M_val, __args._M_order);
+ __res._M_has_val = true;
+ if (__res._M_val != __args._M_old)
+ {
+ __res._M_timeout = false;
+ return __res;
+ }
}
- return { ._M_val = __val, ._M_has_val = true, ._M_timeout = true };
+ __res._M_timeout = true;
+ return __res;
}
} // namespace
--
2.49.0
