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/* Unlock a rwlock. Generic version.
Copyright (C) 2000-2020 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 <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_wait (&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)
{
unsigned n = 0;
__pthread_queue_iterate (rwlock->__readerqueue, wakeup)
n++;
{
struct __pthread *wakeups[n];
unsigned i = 0;
__pthread_dequeuing_iterate (rwlock->__readerqueue, wakeup)
wakeups[i++] = wakeup;
rwlock->__readers += n;
rwlock->__readerqueue = 0;
__pthread_spin_unlock (&rwlock->__lock);
for (i = 0; i < n; i++)
__pthread_wakeup (wakeups[i]);
}
return 0;
}
/* Noone is waiting. Just unlock it. */
__pthread_spin_unlock (&rwlock->__held);
__pthread_spin_unlock (&rwlock->__lock);
return 0;
}
weak_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock);
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