[PATCH v2 10/11] libstdc++ timed_mutex: Ensure that try_lock_for waits for long enough

[Mike Crowe]

The user-defined clock used with shared_mutex::try_lock_for and
shared_mutex::try_lock_shared_for may have higher precision than
__clock_t. We may need to round the duration up to ensure that the timeout
is long enough. (See __timed_mutex_impl::_M_try_lock_for)

        * include/std/shared_mutex: (try_lock_for) Round up wait duration
          if necessary. (try_lock_shared_for) Likewise.
---
 libstdc++-v3/include/std/shared_mutex | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/std/shared_mutex 
b/libstdc++-v3/include/std/shared_mutex
index b637bdc..6e67324 100644
--- a/libstdc++-v3/include/std/shared_mutex
+++ b/libstdc++-v3/include/std/shared_mutex
@@ -471,9 +471,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _Rep, typename _Period>
       bool
-      try_lock_for(const chrono::duration<_Rep, _Period>& __rel_time)
+      try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
       {
-       return try_lock_until(__clock_t::now() + __rel_time);
+        auto __rt = chrono::duration_cast<__clock_t::duration>(__rtime);
+        if (ratio_greater<__clock_t::period, _Period>())
+          ++__rt;
+       return try_lock_until(__clock_t::now() + __rt);
       }
 
     // Shared ownership
@@ -484,9 +487,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _Rep, typename _Period>
       bool
-      try_lock_shared_for(const chrono::duration<_Rep, _Period>& __rel_time)
+      try_lock_shared_for(const chrono::duration<_Rep, _Period>& __rtime)
       {
-       return try_lock_shared_until(__clock_t::now() + __rel_time);
+        auto __rt = chrono::duration_cast<__clock_t::duration>(__rtime);
+        if (ratio_greater<__clock_t::period, _Period>())
+          ++__rt;
+       return try_lock_shared_until(__clock_t::now() + __rt);
       }
 
 #if _GLIBCXX_USE_PTHREAD_RWLOCK_T && _GTHREAD_USE_MUTEX_TIMEDLOCK
-- 
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