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

/****************************************************************************
 * libc/semaphore/sem_getvalue.c
 *
 *   Copyright (C) 2007-2009, 2011 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 <semaphore.h>
#include <errno.h>

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

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

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

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

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

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

/****************************************************************************
 * Function:  sem_getvalue
 *
 * Description:
 *   This function updates the location referenced by 'sval' argument to
 *   have the value of the semaphore referenced by 'sem' without effecting
 *   the state of the semaphore.  The updated value represents the actual
 *   semaphore value that occurred at some unspecified time during the call,
 *   but may not reflect the actual value of the semaphore when it is
 *   returned to the calling task.
 *
 *   If 'sem' is locked, the value return by sem_getvalue() will either be
 *   zero or a negative number whose absolute value represents the number
 *   of tasks waiting for the semaphore.
 *
 * Parameters:
 *   sem - Semaphore descriptor
 *   sval - Buffer by which the value is returned
 *
 * Return Value:
 *   0 (OK), or -1 (ERROR) if unsuccessful
 *
 * Assumptions:
 *
 ****************************************************************************/

int sem_getvalue(FAR sem_t *sem, FAR int *sval)
{
  if (sem && sval)
    {
      *sval = sem->semcount;
      return OK;
    }
  else
    {
      set_errno(EINVAL);
	  return ERROR;
    }
}