incubator-nuttx/sched/pthread/pthread_mutexunlock.c

231 lines
7.6 KiB
C

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