px4-firmware/nuttx/libc/semaphore/sem_init.c

/****************************************************************************
 * libc/sem/sem_init.c
 *
 *   Copyright (C) 2007-2009, 2011-2012 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 <sys/types.h>
#include <limits.h>
#include <semaphore.h>
#include <errno.h>

/****************************************************************************
 * Definitions
 ****************************************************************************/

/****************************************************************************
 * Private Type Declarations
 ****************************************************************************/

/****************************************************************************
 * Global Variables
 ****************************************************************************/

/****************************************************************************
 * Private Variables
 ****************************************************************************/

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Function: sem_init
 *
 * Description:
 *   This function initializes the UNAMED semaphore sem. Following a
 *   successful call to sem_init(), the semaophore may be used in subsequent
 *   calls to sem_wait(), sem_post(), and sem_trywait().  The semaphore
 *   remains usable until it is destroyed.
 *
 *   Only sem itself may be used for performing synchronization. The result
 *   of referring to copies of sem in calls to sem_wait(), sem_trywait(),
 *   sem_post(), and sem_destroy() is undefined.
 *
 * Parameters:
 *   sem - Semaphore to be initialized
 *   pshared - Process sharing (not used)
 *   value - Semaphore initialization value
 *
 * Return Value:
 *   0 (OK), or -1 (ERROR) if unsuccessful.
 *
 * Assumptions:
 *
 ****************************************************************************/

int sem_init(FAR sem_t *sem, int pshared, unsigned int value)
{
  /* Verify that a semaphore was provided and the count is within the valid
   * range.
   */

  if (sem && value <= SEM_VALUE_MAX)
    {
      /* Initialize the seamphore count */

      sem->semcount      = (int16_t)value;

      /* Initialize to support priority inheritance */

#ifdef CONFIG_PRIORITY_INHERITANCE
#  if CONFIG_SEM_PREALLOCHOLDERS > 0
      sem->hhead         = NULL;
#  else
      sem->holder.htcb   = NULL;
      sem->holder.counts = 0;
#  endif
#endif
      return OK;
    }
  else
    {
      set_errno(EINVAL);
      return ERROR;
    }
}