/****************************************************************************
* sched/pthread_mutexlock.c
*
* Copyright (C) 2007-2009 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 <errno.h>
#include <debug.h>
#include "pthread_internal.h"
/****************************************************************************
* Definitions
****************************************************************************/
/****************************************************************************
* Private Type Declarations
****************************************************************************/
/****************************************************************************
* Global Variables
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: pthread_mutex_lock
*
* Description:
* The mutex object referenced by mutex is locked by calling
* pthread_mutex_lock(). If the mutex is already locked, the calling thread
* blocks until the mutex becomes available. This operation returns with the
* mutex object referenced by mutex in the locked state with the calling
* thread as its owner.
*
* If the mutex type is PTHREAD_MUTEX_NORMAL, deadlock detection is not
* provided. Attempting to relock the mutex causes deadlock. If a thread
* attempts to unlock a mutex that it has not locked or a mutex which is
* unlocked, undefined behavior results.
*
* If the mutex type is PTHREAD_MUTEX_ERRORCHECK, then error checking is
* provided. If a thread attempts to relock a mutex that it has already
* locked, an error will be returned. If a thread attempts to unlock a
* mutex that it has not locked or a mutex which is unlocked, an error will
* be returned.
*
* If the mutex type is PTHREAD_MUTEX_RECURSIVE, then the mutex maintains
* the concept of a lock count. When a thread successfully acquires a mutex
* for the first time, the lock count is set to one. Every time a thread
* relocks this mutex, the lock count is incremented by one. Each time the
* thread unlocks the mutex, the lock count is decremented by one. When the
* lock count reaches zero, the mutex becomes available for other threads to
* acquire. If a thread attempts to unlock a mutex that it has not locked or
* a mutex which is unlocked, an error will be returned.
*
* 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_lock().
*
* Assumptions:
*
****************************************************************************/
int pthread_mutex_lock(FAR pthread_mutex_t *mutex)
{
int mypid = (int)getpid();
int ret = OK;
sdbg("mutex=0x%p\n", mutex);
if (!mutex)
{
ret = EINVAL;
}
else
{
/* Make sure the semaphore is stable while we make the following
* checks. This all needs to be one atomic action.
*/
sched_lock();
/* Does this task already hold the semaphore? */
if (mutex->pid == mypid)
{
/* Yes.. Is this a recursive mutex? */
#ifdef CONFIG_MUTEX_TYPES
if (mutex->type == PTHREAD_MUTEX_RECURSIVE)
{
/* Yes... just increment the number of locks held and return success */
mutex->nlocks++;
}
else
#endif
{
/* No, then we would deadlock... return an error (default behavior
* is like PTHREAD_MUTEX_ERRORCHECK)
*/
sdbg("Returning EDEADLK\n");
ret = EDEADLK;
}
}
else
{
/* Take the semaphore */
ret = pthread_takesemaphore((sem_t*)&mutex->sem);
/* If we succussfully obtained the semaphore, then indicate
* that we own it.
*/
if (!ret)
{
mutex->pid = mypid;
#ifdef CONFIG_MUTEX_TYPES
mutex->nlocks = 1;
#endif
}
}
sched_unlock();
}
sdbg("Returning %d\n", ret);
return ret;
}
