This cleans up the implementation of atomic_timed_wait.h and fixes the
accidental pessimization of spinning after waiting in
__timed_waiter_pool::_M_do_wait_until.
libstdc++-v3/ChangeLog:
* include/bits/atomic_timed_wait.h (__wait_clock_t): Define
conditionally.
(__cond_wait_until_impl): Define conditionally.
(__cond_wait_until): Define conditionally. Simplify clock
type detection/conversion.
(__timed_waiter_pool::_M_do_wait_until): Move the spin above
the wait.
---
libstdc++-v3/include/bits/atomic_timed_wait.h | 26 ++++++++++---------
1 file changed, 14 insertions(+), 12 deletions(-)
diff --git a/libstdc++-v3/include/bits/atomic_timed_wait.h
b/libstdc++-v3/include/bits/atomic_timed_wait.h
index ec7ff51cdbc..19386e5806a 100644
--- a/libstdc++-v3/include/bits/atomic_timed_wait.h
+++ b/libstdc++-v3/include/bits/atomic_timed_wait.h
@@ -51,7 +51,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace __detail
{
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX || _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
using __wait_clock_t = chrono::steady_clock;
+#else
+ using __wait_clock_t = chrono::system_clock;
+#endif
template<typename _Clock, typename _Dur>
__wait_clock_t::time_point
@@ -133,11 +137,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return false;
}
}
-#else
+// #elsif <some other platform mechanism,>
// define _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT and implement
__platform_wait_until()
// if there is a more efficient primitive supported by the platform
// (e.g. __ulock_wait())which is better than pthread_cond_clockwait
-#endif // ! PLATFORM_TIMED_WAIT
+#else
+// Use wait on condition variable
// Returns true if wait ended before timeout.
// _Clock must be either steady_clock or system_clock.
@@ -173,12 +178,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__cond_wait_until(__condvar& __cv, mutex& __mx,
const chrono::time_point<_Clock, _Dur>& __atime)
{
-#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
- if constexpr (is_same_v<_Clock, chrono::steady_clock>)
- return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
- else
-#endif
- if constexpr (is_same_v<_Clock, chrono::system_clock>)
+ if constexpr (is_same_v<__wait_clock_t, _Clock>)
return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
else
{
@@ -194,6 +194,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return false;
}
}
+#endif // ! PLATFORM_TIMED_WAIT
struct __timed_waiter_pool : __waiter_pool_base
{
@@ -300,17 +301,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
const chrono::time_point<_Clock, _Dur>&
__atime) noexcept
{
+
for (auto __now = _Clock::now(); __now < __atime;
__now = _Clock::now())
{
+ if (__base_type::_M_do_spin(__pred, __val,
+ __timed_backoff_spin_policy(__atime, __now)))
+ return true;
+
if (__base_type::_M_w._M_do_wait_until(
__base_type::_M_addr, __val, __atime)
&& __pred())
return true;
-
- if (__base_type::_M_do_spin(__pred, __val,
- __timed_backoff_spin_policy(__atime, __now)))
- return true;
}
return false;
}
--
2.26.2
