Add threaded test of sem_trywait

All the existing glibc tests of sem_trywait are single-threaded.  Add
one that calls sem_trywait and sem_post in separate threads.

Tested for x86_64.

2 files changed, 78 insertions, 0 deletions

diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index 2fee4a3..f2c2053 100644
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -257,6 +257,7 @@ tests += \
   tst-sem15 \
   tst-sem16 \
   tst-sem18 \
+  tst-sem19 \
   tst-setuid3 \
   tst-signal1 \
   tst-signal2 \
diff --git a/sysdeps/pthread/tst-sem19.c b/sysdeps/pthread/tst-sem19.c
new file mode 100644
index 0000000..9ef461e
--- /dev/null
+++ b/sysdeps/pthread/tst-sem19.c
@@ -0,0 +1,77 @@
+/* Test sem_trywait with threads.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <support/check.h>
+#include <support/xthread.h>
+
+/* The test uses two threads, the main thread and a newly created
+   thread to test the operation of sem_trywait in a threaded scenario.
+   The intent is to test sem_trywait when it would return EAGAIN, and
+   then again after the critical section in the new thread has posted
+   to the semaphore and the main thread succeeds in calling
+   sem_trywait.  It is possible this test fails with a timeout if the
+   second thread takes longer than the test timeout to acquire the
+   lock, and post.  */
+
+static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
+static sem_t sem;
+
+static void *
+tf (void *arg)
+{
+  xpthread_mutex_lock (&lock);
+  sem_post (&sem);
+  xpthread_mutex_unlock (&lock);
+  return NULL;
+}
+
+static int
+do_test (void)
+{
+  int ret;
+
+  ret = sem_init (&sem, 0, 0);
+  TEST_VERIFY_EXIT (ret == 0);
+  xpthread_mutex_lock (&lock);
+  pthread_t th = xpthread_create (NULL, tf, NULL);
+  errno = 0;
+  /* The other thread is waiting on the lock before it calls sem_post,
+     so sem_trywait should fail.  */
+  ret = sem_trywait (&sem);
+  TEST_COMPARE (ret, -1);
+  TEST_COMPARE (errno, EAGAIN);
+  xpthread_mutex_unlock (&lock);
+  /* The other thread now takes the lock, calls sem_post and releases
+     the lock.  */
+  for (;;)
+    {
+      errno = 0;
+      ret = sem_trywait (&sem);
+      if (ret == 0)
+	break;
+      TEST_COMPARE (errno, EAGAIN);
+    }
+  xpthread_join (th);
+
+  return 0;
+}
+
+#include <support/test-driver.c>