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/* Copyright (C) 2017 Free Software Foundation, Inc.
Contributed by Agustina Arzille <avarzille@riseup.net>, 2017.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU 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 General Public License for more details.
You should have received a copy of the GNU General Public
License along with this program; if not, see
<http://www.gnu.org/licenses/>.
*/
#include <kern/kmutex.h>
#include <kern/atomic.h>
#include <kern/sched_prim.h>
#include <kern/thread.h>
void kmutex_init (struct kmutex *mtxp)
{
mtxp->state = KMUTEX_AVAIL;
simple_lock_init (&mtxp->lock);
}
kern_return_t kmutex_lock (struct kmutex *mtxp, boolean_t interruptible)
{
check_simple_locks ();
if (atomic_cas_acq (&mtxp->state, KMUTEX_AVAIL, KMUTEX_LOCKED))
/* Unowned mutex - We're done. */
return (KERN_SUCCESS);
/* The mutex is locked. We may have to sleep. */
simple_lock (&mtxp->lock);
if (atomic_swap_acq (&mtxp->state, KMUTEX_CONTENDED) == KMUTEX_AVAIL)
{
/* The mutex was released in-between. */
simple_unlock (&mtxp->lock);
return (KERN_SUCCESS);
}
/* Sleep and check the result value of the waiting, in order to
* inform our caller if we were interrupted or not. Note that
* we don't need to set again the mutex state. The owner will
* handle that in every case. */
thread_sleep ((event_t)mtxp, (simple_lock_t)&mtxp->lock, interruptible);
return (current_thread()->wait_result == THREAD_AWAKENED ?
KERN_SUCCESS : KERN_INTERRUPTED);
}
kern_return_t kmutex_trylock (struct kmutex *mtxp)
{
return (atomic_cas_acq (&mtxp->state, KMUTEX_AVAIL, KMUTEX_LOCKED) ?
KERN_SUCCESS : KERN_FAILURE);
}
void kmutex_unlock (struct kmutex *mtxp)
{
if (atomic_cas_rel (&mtxp->state, KMUTEX_LOCKED, KMUTEX_AVAIL))
/* No waiters - We're done. */
return;
simple_lock (&mtxp->lock);
if (!thread_wakeup_one ((event_t)mtxp))
/* Any threads that were waiting on this mutex were
* interrupted and left - Reset the mutex state. */
mtxp->state = KMUTEX_AVAIL;
simple_unlock (&mtxp->lock);
}
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