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/* Test sem_trywait with threads.
Copyright (C) 2024-2025 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>
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