[gcc r16-4429] libstdc++: Add std::future tests for negative timeouts [PR116586]

[Jonathan Wakely]

https://gcc.gnu.org/g:bb96099a8dc8cf69bb0d2e424c3b38e6365f90f6

commit r16-4429-gbb96099a8dc8cf69bb0d2e424c3b38e6365f90f6
Author: Mike Crowe <mac@mcrowe.com>
Date:   Sun Sep 14 21:21:31 2025 +0100

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

Diff:
---
 .../testsuite/30_threads/future/members/116586.cc  | 55 ++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/libstdc++-v3/testsuite/30_threads/future/members/116586.cc b/libstdc++-v3/testsuite/30_threads/future/members/116586.cc
new file mode 100644
index 000000000000..b7cd12c6009c
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/future/members/116586.cc
@@ -0,0 +1,55 @@
+// { dg-do run { target c++11 } }
+
+#include <future>
+#include <chrono>
+#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::promise<int> p;
+  std::future<int> f = p.get_future();
+  const chrono::time_point<Clock> tp(offset);
+  VERIFY(f.wait_until(tp) == std::future_status::timeout);
+}
+
+// The type of clock used for the actual wait depends on whether
+// _GLIBCXX_HAVE_LINUX_FUTEX is defined.  We might as well just test both
+// steady_clock and system_clock.
+template <typename Clock>
+void
+test_relative(chrono::nanoseconds offset)
+{
+  std::promise<int> p;
+  std::future<int> f = p.get_future();
+  const auto d = -Clock::now().time_since_epoch() + offset;
+  VERIFY(f.wait_for(d) == std::future_status::timeout);
+}
+
+int main()
+{
+  // 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);
+  }
+}