libstdc++: Avoid rounding errors on custom clocks in condition_variable

The fix for PR68519 in 83fd5e73b3c16296e0d7ba54f6c547e01c7eae7b only
applied to condition_variable::wait_for. This problem can also apply to
condition_variable::wait_until but only if the custom clock is using a
more recent epoch so that a small enough delta can be calculated. let's
use the newly-added chrono::__detail::ceil to fix this and also make use
of that function to simplify the previous wait_for fixes.

Also, simplify the existing test case for PR68519 a little and make its
variables local so we can add a new test case for the above problem.
Unfortunately, the test would have only started failing if sufficient
time has passed since the chrono::steady_clock epoch had passed anyway,
but it's better than nothing.

libstdc++-v3/ChangeLog:

	* include/std/condition_variable (condition_variable::wait_until):
	Convert delta to steady_clock duration before adding to current
	steady_clock time to avoid rounding errors described in PR68519.
	(condition_variable::wait_for): Simplify calculation of absolute
	time by using chrono::__detail::ceil in both overloads.
	* testsuite/30_threads/condition_variable/members/68519.cc:
	(test_wait_for): Renamed from test01. Replace unassigned val
	variable with constant false. Reduce scope of mx and cv
	variables to just test_wait_for function.
	(test_wait_until): Add new test case.

1 files changed, 9 insertions, 9 deletions

diff --git a/libstdc++-v3/include/std/condition_variable b/libstdc++-v3/include/std/condition_variable
index a08cfc6..1abec54 100644
--- a/libstdc++-v3/include/std/condition_variable
+++ b/libstdc++-v3/include/std/condition_variable
@@ -133,10 +133,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if __cplusplus > 201703L
 	static_assert(chrono::is_clock_v<_Clock>);
 #endif
+	using __s_dur = typename __clock_t::duration;
 	const typename _Clock::time_point __c_entry = _Clock::now();
 	const __clock_t::time_point __s_entry = __clock_t::now();
 	const auto __delta = __atime - __c_entry;
-	const auto __s_atime = __s_entry + __delta;
+	const auto __s_atime = __s_entry +
+	  chrono::__detail::ceil<__s_dur>(__delta);
 
 	if (__wait_until_impl(__lock, __s_atime) == cv_status::no_timeout)
 	  return cv_status::no_timeout;
@@ -166,10 +168,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	       const chrono::duration<_Rep, _Period>& __rtime)
       {
 	using __dur = typename steady_clock::duration;
-	auto __reltime = chrono::duration_cast<__dur>(__rtime);
-	if (__reltime < __rtime)
-	  ++__reltime;
-	return wait_until(__lock, steady_clock::now() + __reltime);
+	return wait_until(__lock,
+			  steady_clock::now() +
+			  chrono::__detail::ceil<__dur>(__rtime));
       }
 
     template<typename _Rep, typename _Period, typename _Predicate>
@@ -179,10 +180,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	       _Predicate __p)
       {
 	using __dur = typename steady_clock::duration;
-	auto __reltime = chrono::duration_cast<__dur>(__rtime);
-	if (__reltime < __rtime)
-	  ++__reltime;
-	return wait_until(__lock, steady_clock::now() + __reltime,
+	return wait_until(__lock,
+			  steady_clock::now() +
+			  chrono::__detail::ceil<__dur>(__rtime),
 			  std::move(__p));
       }