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/* Try to acquire a rwlock for reading. Generic version.
Copyright (C) 2002-2020 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 <pthread.h>
#include <assert.h>
#include <pt-internal.h>
/* Try to acquire RWLOCK. */
int
pthread_rwlock_tryrdlock (struct __pthread_rwlock *rwlock)
{
__pthread_spin_wait (&rwlock->__lock);
if (__pthread_spin_trylock (&rwlock->__held) == 0)
/* Successfully acquired the lock. */
{
assert (rwlock->__readerqueue == 0);
assert (rwlock->__writerqueue == 0);
assert (rwlock->__readers == 0);
rwlock->__readers = 1;
__pthread_spin_unlock (&rwlock->__lock);
return 0;
}
else
/* Lock is held, but is held by a reader? */
if (rwlock->__readers > 0)
{
assert (rwlock->__readerqueue == 0);
rwlock->__readers++;
__pthread_spin_unlock (&rwlock->__lock);
return 0;
}
/* The lock is busy. */
__pthread_spin_unlock (&rwlock->__lock);
return EBUSY;
}
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