nuttx/sched/pthread/pthread_mutextrylock.c

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/****************************************************************************
* sched/pthread/pthread_mutextrylock.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 <semaphore.h>
#include <sched.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>
#include "pthread/pthread.h"
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: pthread_mutex_trylock
*
* Description:
* The function pthread_mutex_trylock() is identical to pthread_mutex_lock()
* except that if the mutex object referenced by mutex is currently locked
* (by any thread, including the current thread), the call returns immediately
* with the errno EBUSY.
*
* 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:
* mutex - A reference to the mutex to be locked.
*
* Return Value:
* 0 on success or an errno value on failure. Note that the errno EINTR
* is never returned by pthread_mutex_trylock().
*
* Assumptions:
*
* POSIX Compatibility:
* - This implementation does not return EAGAIN when the mutex could not be
* acquired because the maximum number of recursive locks for mutex has
* been exceeded.
*
****************************************************************************/
int pthread_mutex_trylock(FAR pthread_mutex_t *mutex)
{
int status;
int ret = EINVAL;
sinfo("mutex=0x%p\n", mutex);
DEBUGASSERT(mutex != NULL);
if (mutex != NULL)
{
int mypid = (int)getpid();
/* Make sure the semaphore is stable while we make the following
* checks. This all needs to be one atomic action.
*/
sched_lock();
/* Try to get the semaphore. */
status = pthread_mutex_trytake(mutex);
if (status == OK)
{
/* If we successfully obtained the semaphore, then indicate
* that we own it.
*/
mutex->pid = mypid;
#ifdef CONFIG_PTHREAD_MUTEX_TYPES
if (mutex->type == PTHREAD_MUTEX_RECURSIVE)
{
mutex->nlocks = 1;
}
#endif
ret = OK;
}
/* pthread_mutex_trytake failed. Did it fail because the semaphore
* was not avaialable?
*/
else if (status == EAGAIN)
{
#ifdef CONFIG_PTHREAD_MUTEX_TYPES
/* Check if recursive mutex was locked by the calling thread. */
if (mutex->type == PTHREAD_MUTEX_RECURSIVE && mutex->pid == mypid)
{
/* Increment the number of locks held and return successfully. */
if (mutex->nlocks < INT16_MAX)
{
mutex->nlocks++;
ret = OK;
}
else
{
ret = EOVERFLOW;
}
}
else
#endif
#ifndef CONFIG_PTHREAD_MUTEX_UNSAFE
/* The calling thread does not hold the semaphore. The correct
* behavior for the 'robust' mutex is to verify that the holder of
* the mutex is still valid. This is protection from the case
* where the holder of the mutex has exitted without unlocking it.
*/
#ifdef CONFIG_PTHREAD_MUTEX_BOTH
#ifdef CONFIG_PTHREAD_MUTEX_TYPES
/* Check if this NORMAL mutex is robust */
if (mutex->pid > 0 &&
((mutex->flags & _PTHREAD_MFLAGS_ROBUST) != 0 ||
mutex->type != PTHREAD_MUTEX_NORMAL) &&
sched_gettcb(mutex->pid) == NULL)
#else /* CONFIG_PTHREAD_MUTEX_TYPES */
/* Check if this NORMAL mutex is robust */
if (mutex->pid > 0 &&
(mutex->flags & _PTHREAD_MFLAGS_ROBUST) != 0 &&
sched_gettcb(mutex->pid) == NULL)
#endif /* CONFIG_PTHREAD_MUTEX_TYPES */
#else /* CONFIG_PTHREAD_MUTEX_ROBUST */
/* This mutex is always robust, whatever type it is. */
if (mutex->pid > 0 && sched_gettcb(mutex->pid) == NULL)
#endif
{
DEBUGASSERT(mutex->pid != 0); /* < 0: available, >0 owned, ==0 error */
DEBUGASSERT((mutex->flags & _PTHREAD_MFLAGS_INCONSISTENT) != 0);
/* A thread holds the mutex, but there is no such thread.
* POSIX requires that the 'robust' mutex return EOWNERDEAD
* in this case. It is then the caller's responsibility to
* call pthread_mutx_consistent() fo fix the mutex.
*/
mutex->flags |= _PTHREAD_MFLAGS_INCONSISTENT;
ret = EOWNERDEAD;
}
/* The mutex is locked by another, active thread */
else
#endif /* CONFIG_PTHREAD_MUTEX_UNSAFE */
{
ret = EBUSY;
}
}
/* Some other, unhandled error occurred */
else
{
ret = status;
}
sched_unlock();
}
sinfo("Returning %d\n", ret);
return ret;
}