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/* Copyright (C) 2015-2022 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/>. */
/* This tests that a writer that is preferred -- but times out due to a
reader being present -- does not miss to wake other readers blocked on the
writer's pending lock acquisition. */
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
/* The bug existed in the code that strictly prefers writers over readers. */
static pthread_rwlock_t r = PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP;
static void *
writer (void *arg)
{
struct timespec ts;
if (clock_gettime (CLOCK_REALTIME, &ts) != 0)
{
puts ("clock_gettime failed");
exit (EXIT_FAILURE);
}
ts.tv_sec += 1;
int e = pthread_rwlock_timedwrlock (&r, &ts);
if (e != ETIMEDOUT)
{
puts ("timedwrlock did not time out");
exit (EXIT_FAILURE);
}
return NULL;
}
static void *
reader (void *arg)
{
/* This isn't a reliable way to get the interleaving we need (because a
failed trylock doesn't synchronize with the writer, and because we could
try to lock after the writer has already timed out). However, both will
just lead to false positives. */
int e;
while ((e = pthread_rwlock_tryrdlock (&r)) != EBUSY)
{
if (e != 0)
exit (EXIT_FAILURE);
pthread_rwlock_unlock (&r);
}
e = pthread_rwlock_rdlock (&r);
if (e != 0)
{
puts ("reader rdlock failed");
exit (EXIT_FAILURE);
}
pthread_rwlock_unlock (&r);
return NULL;
}
static int
do_test (void)
{
/* Grab a rdlock, then create a writer and a reader, and wait until they
finished. */
if (pthread_rwlock_rdlock (&r) != 0)
{
puts ("initial rdlock failed");
return 1;
}
pthread_t thw;
if (pthread_create (&thw, NULL, writer, NULL) != 0)
{
puts ("create failed");
return 1;
}
pthread_t thr;
if (pthread_create (&thr, NULL, reader, NULL) != 0)
{
puts ("create failed");
return 1;
}
if (pthread_join (thw, NULL) != 0)
{
puts ("writer join failed");
return 1;
}
if (pthread_join (thr, NULL) != 0)
{
puts ("reader join failed");
return 1;
}
return 0;
}
#define TEST_FUNCTION do_test ()
#include "../test-skeleton.c"
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