text: /****************************************************************************
   *
   * Copyright 2016 Samsung Electronics All Rights Reserved.
   *
   * Licensed 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.
   *
   ****************************************************************************/
  /****************************************************************************
   * kernel/pthread/pthread_mutexunlock.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 <tinyara/config.h>
  
  #include <unistd.h>
  #include <pthread.h>
  #include <sched.h>
  #include <errno.h>
  #include <debug.h>
  
  #include "pthread/pthread.h"
  
  /****************************************************************************
   * Definitions
   ****************************************************************************/
  
  /****************************************************************************
   * Private Type Declarations
   ****************************************************************************/
  
  /****************************************************************************
   * Global Variables
   ****************************************************************************/
  
  /****************************************************************************
   * Private Variables
   ****************************************************************************/
  
  /****************************************************************************
   * Private Functions
   ****************************************************************************/
  
  /****************************************************************************
   * 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 = EINVAL;
  
  	svdbg("mutex=0x%p\n", mutex);
  	DEBUGASSERT(mutex != NULL);
  
  	/* Make sure the semaphore is stable while we make the following checks.
  	 * This all needs to be one atomic action.
  	 */
  	sched_lock();
  	if (mutex != NULL) {
  #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 error (default behavior is like PTHREAD_MUTEX_ERRORCHECK) */
  
  			sdbg("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();
  	svdbg("Returning %d\n", ret);
  	return ret;
  }
  