/****************************************************************************
* sched/pthread/pthread_mutexunlock.c
*
* Copyright (C) 2007-2009, 2017 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* 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_unlock
*
* Description:
* Return true is the mutex is locked.
*
* Parameters:
* None
*
* Return 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.
*
* Parameters:
* None
*
* Return Value:
* None
*
* Assumptions:
*
****************************************************************************/
int pthread_mutex_unlock(FAR pthread_mutex_t *mutex)
{
int ret = OK;
sinfo("mutex=0x%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.
*/
sched_lock();
/* The unlock operation is only performed if the mutex is actually locked.
* If the mutex is not locked, then SUCCESS will be returned (there is
* no error return value specified for this 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 != (int)getpid())
#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 != (int)getpid())
#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 != (int)getpid())
#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 = -1;
#ifdef CONFIG_PTHREAD_MUTEX_TYPES
mutex->nlocks = 0;
#endif
ret = pthread_mutex_give(mutex);
}
}
sched_unlock();
sinfo("Returning %d\n", ret);
return ret;
}