229 lines
7.5 KiB
C
229 lines
7.5 KiB
C
/****************************************************************************
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* sched/pthread/pthread_mutexunlock.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <unistd.h>
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#include <pthread.h>
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#include <sched.h>
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#include <assert.h>
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#include <errno.h>
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#include <debug.h>
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#include "pthread/pthread.h"
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Name: pthread_mutex_islocked
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*
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* Description:
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* Return true is the mutex is locked.
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*
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* Input Parameters:
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* None
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*
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* Returned Value:
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* Returns true if the mutex is locked
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*
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****************************************************************************/
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static inline bool pthread_mutex_islocked(FAR struct pthread_mutex_s *mutex)
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{
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int semcount = mutex->sem.semcount;
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/* The underlying semaphore should have a count less than 2:
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*
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* 1 == mutex is unlocked.
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* 0 == mutex is locked with no waiters
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* -n == mutex is locked with 'n' waiters.
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*/
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DEBUGASSERT(semcount < 2);
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return semcount < 1;
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: pthread_mutex_unlock
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*
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* Description:
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* The pthread_mutex_unlock() function releases the mutex object referenced
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* by mutex. The manner in which a mutex is released is dependent upon the
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* mutex's type attribute. If there are threads blocked on the mutex object
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* referenced by mutex when pthread_mutex_unlock() is called, resulting in
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* the mutex becoming available, the scheduling policy is used to determine
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* which thread shall acquire the mutex. (In the case of
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* PTHREAD_MUTEX_RECURSIVE mutexes, the mutex becomes available when the
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* count reaches zero and the calling thread no longer has any locks on
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* this mutex).
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*
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* If a signal is delivered to a thread waiting for a mutex, upon return
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* from the signal handler the thread resumes waiting for the mutex as if
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* it was not interrupted.
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*
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* Input Parameters:
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* None
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*
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* Returned Value:
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* None
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*
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* Assumptions:
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*
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****************************************************************************/
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int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
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{
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int ret = EPERM;
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sinfo("mutex=%p\n", mutex);
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DEBUGASSERT(mutex != NULL);
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if (mutex == NULL)
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{
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return EINVAL;
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}
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/* Make sure the semaphore is stable while we make the following checks.
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* This all needs to be one atomic action.
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*/
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sched_lock();
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/* The unlock operation is only performed if the mutex is actually locked.
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* EPERM *must* be returned if the mutex type is PTHREAD_MUTEX_ERRORCHECK
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* or PTHREAD_MUTEX_RECURSIVE, or the mutex is a robust mutex, and the
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* current thread does not own the mutex. Behavior is undefined for the
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* remaining case.
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*/
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if (pthread_mutex_islocked(mutex))
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{
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#if !defined(CONFIG_PTHREAD_MUTEX_UNSAFE) || defined(CONFIG_PTHREAD_MUTEX_TYPES)
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/* Does the calling thread own the semaphore? If no, should we return
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* an error?
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*
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* Error checking is always performed for ERRORCHECK and RECURSIVE
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* mutex types. Error checking is only performed for NORMAL (or
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* DEFAULT) mutex type if the NORMAL mutex is robust. That is either:
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*
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* 1. CONFIG_PTHREAD_MUTEX_ROBUST is defined, or
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* 2. CONFIG_PTHREAD_MUTEX_BOTH is defined and the robust flag is set
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*/
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#if defined(CONFIG_PTHREAD_MUTEX_ROBUST)
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/* Not that error checking is always performed if the configuration has
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* CONFIG_PTHREAD_MUTEX_ROBUST defined. Just check if the calling
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* thread owns the semaphore.
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*/
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if (mutex->pid != gettid())
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#elif defined(CONFIG_PTHREAD_MUTEX_UNSAFE) && defined(CONFIG_PTHREAD_MUTEX_TYPES)
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/* If mutex types are not supported, then all mutexes are NORMAL (or
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* DEFAULT). Error checking should never be performed for the
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* non-robust NORMAL mutex type.
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*/
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if (mutex->type != PTHREAD_MUTEX_NORMAL && mutex->pid != gettid())
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#else /* CONFIG_PTHREAD_MUTEX_BOTH */
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/* Skip the error check if this is a non-robust NORMAL mutex */
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bool errcheck = ((mutex->flags & _PTHREAD_MFLAGS_ROBUST) != 0);
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#ifdef CONFIG_PTHREAD_MUTEX_TYPES
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errcheck |= (mutex->type != PTHREAD_MUTEX_NORMAL);
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#endif
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/* Does the calling thread own the semaphore? If not should we report
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* the EPERM error?
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*/
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if (errcheck && mutex->pid != gettid())
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#endif
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{
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/* No... return an EPERM error.
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*
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* Per POSIX: "EPERM should be returned if the mutex type is
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* PTHREAD_MUTEX_ERRORCHECK or PTHREAD_MUTEX_RECURSIVE, or the
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* mutex is a robust mutex, and the current thread does not own
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* the mutex."
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*
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* For the case of the non-robust PTHREAD_MUTEX_NORMAL mutex,
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* the behavior is undefined.
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*/
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serr("ERROR: Holder=%d returning EPERM\n", mutex->pid);
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ret = EPERM;
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}
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else
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#endif /* !CONFIG_PTHREAD_MUTEX_UNSAFE || CONFIG_PTHREAD_MUTEX_TYPES */
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#ifdef CONFIG_PTHREAD_MUTEX_TYPES
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/* Yes, the caller owns the semaphore.. Is this a recursive mutex? */
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if (mutex->type == PTHREAD_MUTEX_RECURSIVE && mutex->nlocks > 1)
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{
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/* This is a recursive mutex and we there are multiple locks held.
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* Retain the mutex lock, just decrement the count of locks held,
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* and return success.
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*/
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mutex->nlocks--;
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ret = OK;
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}
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else
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#endif /* CONFIG_PTHREAD_MUTEX_TYPES */
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/* This is either a non-recursive mutex or is the outermost unlock of
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* a recursive mutex.
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*
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* In the case where the calling thread is NOT the holder of the
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* thread, the behavior is undefined per POSIX.
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* Here we do the same as GLIBC:
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* We allow the other thread to release the mutex even though it does
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* not own it.
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*/
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{
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/* Nullify the pid and lock count then post the semaphore */
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mutex->pid = INVALID_PROCESS_ID;
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#ifdef CONFIG_PTHREAD_MUTEX_TYPES
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mutex->nlocks = 0;
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#endif
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ret = pthread_mutex_give(mutex);
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}
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}
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sched_unlock();
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sinfo("Returning %d\n", ret);
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return ret;
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}
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