[gcc r16-4431] libstdc++: Add std::timed_mutex tests for negative timeouts [PR116586]

[Jonathan Wakely]

https://gcc.gnu.org/g:06782e7aac42a38c5e04a223cc73e1964a64c7d1

commit r16-4431-g06782e7aac42a38c5e04a223cc73e1964a64c7d1
Author: Mike Crowe <mac@mcrowe.com>
Date:   Sun Sep 14 21:21:33 2025 +0100

    libstdc++: Add std::timed_mutex tests for negative timeouts [PR116586]
    
    Add tests to show that std::timed_mutex::try_lock_until and
    std::timed_mutex::try_lock_for correctly handle negative timeouts.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/116586
            * testsuite/30_threads/timed_mutex/try_lock_until/116586.cc: New
            test.
    
    Signed-off-by: Mike Crowe <mac@mcrowe.com>

Diff:
---
 .../timed_mutex/try_lock_until/116586.cc           | 57 ++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/libstdc++-v3/testsuite/30_threads/timed_mutex/try_lock_until/116586.cc b/libstdc++-v3/testsuite/30_threads/timed_mutex/try_lock_until/116586.cc
new file mode 100644
index 000000000000..dcba7aa2f8ca
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/timed_mutex/try_lock_until/116586.cc
@@ -0,0 +1,57 @@
+// { dg-do run { target c++11 } }
+
+#include <chrono>
+#include <mutex>
+#include <initializer_list>
+#include <testsuite_hooks.h>
+
+namespace chrono = std::chrono;
+
+// thread.timedmutex.requirements.general:
+//   If abs_time has already passed, the function attempts to obtain
+//   ownership without blocking (as if by calling try_lock()).
+
+template <typename Clock>
+void
+test_absolute(chrono::nanoseconds offset)
+{
+  std::timed_mutex mtx;
+  chrono::time_point<Clock> tp(offset);
+  VERIFY(mtx.try_lock_until(tp));
+  VERIFY(!mtx.try_lock_until(tp));
+}
+
+// The type of clock used for the actual wait depends on whether
+// _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK is defined. We might as well just test
+// both steady_clock and system_clock.
+template <typename Clock>
+void
+test_relative(chrono::nanoseconds offset)
+{
+  std::timed_mutex mtx;
+  const auto d = -Clock::now().time_since_epoch() + offset;
+  VERIFY(mtx.try_lock_for(d));
+  VERIFY(!mtx.try_lock_for(d));
+}
+
+int main()
+{
+  // Try once with an offset that ought to result in tv_sec == 0, tv_nsec < 0
+  // and one with an offset that ought to result in tv_sec < 0, tv_nsec == 0
+  // for the absolute calls at least.  It's not really possible to arrange for
+  // the relative calls to have tv_nsec == 0 due to time advancing.
+  for (const chrono::nanoseconds offset : {
+      // tv_sec == 0, tv_nsec == 0
+      chrono::nanoseconds{0},
+      // tv_sec == 0, tv_nsec < 0
+      chrono::duration_cast<chrono::nanoseconds>(chrono::milliseconds{-10}),
+      // tv_sec < 0
+      chrono::duration_cast<chrono::nanoseconds>(chrono::seconds{-10})
+    }) {
+    test_absolute<chrono::system_clock>(offset);
+    test_relative<chrono::system_clock>(offset);
+
+    test_absolute<chrono::steady_clock>(offset);
+    test_relative<chrono::steady_clock>(offset);
+  }
+}