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/* Test rwlock with PREFER_WRITER_NONRECURSIVE_NP (bug 23861).
Copyright (C) 2018-2025 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 <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <support/xthread.h>
/* We choose 10 iterations because this happens to be able to trigger the
stall on contemporary hardware. */
#define LOOPS 10
/* We need 3 threads to trigger bug 23861. One thread as a writer, and
two reader threads. The test verifies that the second-to-last reader
is able to notify the *last* reader that it should be done waiting.
If the second-to-last reader fails to notify the last reader or does
so incorrectly then the last reader may stall indefinitely. */
#define NTHREADS 3
_Atomic int do_exit;
pthread_rwlockattr_t mylock_attr;
pthread_rwlock_t mylock;
void *
run_loop (void *a)
{
while (!do_exit)
{
if (random () & 1)
{
xpthread_rwlock_wrlock (&mylock);
xpthread_rwlock_unlock (&mylock);
}
else
{
xpthread_rwlock_rdlock (&mylock);
xpthread_rwlock_unlock (&mylock);
}
}
return NULL;
}
int
do_test (void)
{
xpthread_rwlockattr_init (&mylock_attr);
xpthread_rwlockattr_setkind_np (&mylock_attr,
PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
xpthread_rwlock_init (&mylock, &mylock_attr);
for (int n = 0; n < LOOPS; n++)
{
pthread_t tids[NTHREADS];
do_exit = 0;
for (int i = 0; i < NTHREADS; i++)
tids[i] = xpthread_create (NULL, run_loop, NULL);
/* Let the threads run for some time. */
sleep (1);
printf ("Exiting...");
fflush (stdout);
do_exit = 1;
for (int i = 0; i < NTHREADS; i++)
xpthread_join (tids[i]);
printf ("done.\n");
}
pthread_rwlock_destroy (&mylock);
pthread_rwlockattr_destroy (&mylock_attr);
return 0;
}
#define TIMEOUT (DEFAULT_TIMEOUT + 3 * LOOPS)
#include <support/test-driver.c>
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