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/* Unlock a rwlock. Generic version.
Copyright (C) 2000,02 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 Library General Public License as
published by the Free Software Foundation; either version 2 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include <pthread.h>
#include <pt-internal.h>
/* Unlock *RWLOCK, rescheduling a waiting writer thread or, if there
are no threads waiting for a write lock, rescheduling the reader
threads. */
int
pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
struct __pthread *wakeup;
__pthread_spin_lock (&rwlock->__lock);
assert (__pthread_spin_trylock (&rwlock->__held) == EBUSY);
if (rwlock->readers > 1)
/* There are other readers. */
{
rwlock->readers --;
__pthread_spin_unlock (&rwlock->__lock);
return 0;
}
if (rwlock->readers == 1)
/* Last reader. */
rwlock->readers = 0;
/* Wake someone else up. Try the writer queue first, then the
reader queue if that is empty. */
if (rwlock->writerqueue)
{
wakeup = rwlock->writerqueue;
__pthread_dequeue (wakeup);
/* We do not unlock RWLOCK->held: we are transferring the ownership
to the thread that we are waking up. */
__pthread_spin_unlock (&rwlock->__lock);
__pthread_wakeup (wakeup);
return 0;
}
if (rwlock->readerqueue)
{
__pthread_queue_iterate (rwlock->readerqueue, wakeup)
rwlock->readers ++;
wakeup = rwlock->readerqueue;
rwlock->readerqueue = 0;
__pthread_spin_unlock (&rwlock->__lock);
/* We can safely walk the list of waiting threads without holding
the lock since it is now decoupled from the rwlock. */
__pthread_dequeuing_iterate (wakeup, wakeup)
__pthread_wakeup (wakeup);
return 0;
}
/* Noone is waiting. Just unlock it. */
__pthread_spin_unlock (&rwlock->__held);
__pthread_spin_unlock (&rwlock->__lock);
return 0;
}
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