From: Mike Crowe <mac@mcrowe.com>
Date: Sun, 14 Sep 2025 20:21:28 +0000 (+0100)
Subject: libstdc++: Add std::binary_semaphore tests for negative timeouts [PR116586]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e0525a6d2bba07d623424ab6f10a023de90e65a2;p=thirdparty%2Fgcc.git

libstdc++: Add std::binary_semaphore tests for negative timeouts [PR116586]

Add test cases to prove that negative timeouts are correctly handled by
std::binary_semaphore (which is just an alias for
std::counting_semaphore<1>).  The tests exercise cases that aren't
problematic with the current code since system_clock is converted to
steady_clock before calling __platform_wait_until() is called but they
will protect against changes in the implementation reintroducing this
bug.

libstdc++-v3/ChangeLog:

	PR libstdc++/116586
	* testsuite/30_threads/semaphore/try_acquire_for.cc: Add tests.
	* testsuite/30_threads/semaphore/try_acquire_until.cc: Add
	tests.

Signed-off-by: Mike Crowe <mac@mcrowe.com>
---

diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc
index 39681c7ee56..94acb253091 100644
--- a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc
@@ -24,6 +24,7 @@
 #include <chrono>
 #include <thread>
 #include <atomic>
+#include <initializer_list>
 #include <testsuite_hooks.h>
 
 void test01()
@@ -90,9 +91,30 @@ test03()
   s.try_acquire_for(timeout);
 }
 
+// Prove semaphore doesn't suffer from PR116586
+template <typename Clock>
+void
+test_relative(std::chrono::nanoseconds offset)
+{
+  std::binary_semaphore sem(1);
+  VERIFY(sem.try_acquire_for(offset));
+  VERIFY(!sem.try_acquire_for(offset));
+}
+
 int main()
 {
   test01();
   test02();
   test03();
+  using namespace std::chrono;
+  for (const nanoseconds offset : {
+      nanoseconds{0},
+      nanoseconds{-10ms},
+      nanoseconds{-10s}
+    }) {
+    test_relative<std::chrono::system_clock>(offset);
+    test_relative<std::chrono::system_clock>(offset - std::chrono::system_clock::now().time_since_epoch());
+    test_relative<std::chrono::steady_clock>(offset);
+    test_relative<std::chrono::steady_clock>(offset - std::chrono::steady_clock::now().time_since_epoch());
+  }
 }
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc
index de0068d670a..ed6bd118fee 100644
--- a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc
@@ -24,6 +24,7 @@
 #include <chrono>
 #include <thread>
 #include <atomic>
+#include <initializer_list>
 #include <testsuite_hooks.h>
 
 void test01()
@@ -87,8 +88,31 @@ void test02()
   b.wait(1);
 }
 
+// Prove semaphore doesn't suffer from PR116586
+template <typename Clock>
+void
+test_absolute(std::chrono::nanoseconds offset)
+{
+  std::binary_semaphore sem(1);
+  std::chrono::time_point<Clock> tp(offset);
+  VERIFY(sem.try_acquire_until(tp));
+  VERIFY(!sem.try_acquire_until(tp));
+}
+
 int main()
 {
   test01();
   test02();
+  using namespace std::chrono;
+  for (const nanoseconds offset : {
+      // tv_sec == 0, tv_nsec == 0
+      nanoseconds{0},
+      // tv_sec == 0, tv_nsec < 0
+      nanoseconds{-10ms},
+      // tv_sec < 0
+      nanoseconds{-10s}
+    }) {
+    test_absolute<std::chrono::system_clock>(offset);
+    test_absolute<std::chrono::steady_clock>(offset);
+  }
 }