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/* Copyright (C) 2016 Free Software Foundation, Inc.
Contributed by Agustina Arzille <avarzille@riseup.net>, 2016.
This program 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.
This program 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 this program; if not, see
<http://www.gnu.org/licenses/>.
*/
#include <pthread.h>
#include <pt-internal.h>
#include <bits/pt-atomic.h>
#include <hurdlock.h>
#include "pt-rwlock.h"
int __pthread_rwlock_unlock (pthread_rwlock_t *rwp)
{
int flags = rwp->__flags & GSYNC_SHARED;
atomic_read_barrier ();
unsigned int owner = rwl_oid (rwp->__oid_nrd);
if ((owner & ID_MASK) != 0)
{
/* A writer holds the lock. */
if (!rwl_owned_p (rwp, early_pthread_self(), flags))
/* ... But it isn't us. */
return (EPERM);
rwl_spid(rwp) = 0;
rwl_oid(rwp->__oid_nrd) = RWLOCK_UNOWNED;
atomic_write_barrier ();
/* The exclusive lock has been released. Now decide whether
* to wake a queued writer (preferred), or all the queued readers. */
if (rwl_qwr (rwp->__oid_nrd) > 0)
lll_wake (&rwl_qwr(rwp->__oid_nrd), flags);
else if (rwl_nrd (rwp->__oid_nrd) > 0)
lll_wake (&rwl_oid(rwp->__oid_nrd), flags | GSYNC_BROADCAST);
}
else if (rwl_nrd (rwp->__oid_nrd) == 0)
return (EPERM);
else
{
union __hurd_xint tmp;
while (1)
{
tmp.__qv = atomic_loadx (&rwp->__oid_nrd.__qv);
if (catomic_casx_bool (&rwp->__oid_nrd.__qv,
hurd_xint_pair (tmp.__lo, tmp.__hi),
hurd_xint_pair (rwl_nrd (tmp) == 1 ?
RWLOCK_UNOWNED : RWLOCK_RO, rwl_nrd (tmp) - 1)))
break;
}
/* As a reader, we only need to do a wakeup iff:
* - We were the last one.
* - There's at least a writer queued. */
if (rwl_nrd (tmp) == 1 && rwl_qwr (rwp->__oid_nrd) > 0)
lll_wake (&rwl_qwr(rwp->__oid_nrd), flags);
}
return (0);
}
strong_alias (__pthread_rwlock_unlock, pthread_rwlock_unlock)
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