/****************************************************************************
* sched/sem_trywait.c
*
* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* 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 <semaphore.h>
#include <sched.h>
#include <errno.h>
#include <nuttx/arch.h>
#include "os_internal.h"
#include "sem_internal.h"
/****************************************************************************
* Definitions
****************************************************************************/
/****************************************************************************
* Private Type Declarations
****************************************************************************/
/****************************************************************************
* Global Variables
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Function: sem_trywait
*
* Description:
* This function locks the specified semaphore only if the
* semaphore is currently not locked. Otherwise, it locks
* the semaphore. In either case, the call returns without
* blocking.
*
* Parameters:
* sem - the semaphore descriptor
*
* Return Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
* If this function returns -1 (ERROR), then the cause
* of the failure will be reported in "errno" as:
* - EINVAL: Invalid attempt to get the semaphore
* - EAGAIN: The semaphore is not available.
*
* Assumptions:
*
****************************************************************************/
int sem_trywait(FAR sem_t *sem)
{
FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head;
irqstate_t saved_state;
int ret = ERROR;
/* This API should not be called from interrupt handlers */
DEBUGASSERT(up_interrupt_context() == FALSE)
/* Assume any errors reported are due to invalid arguments. */
*get_errno_ptr() = EINVAL;
if (sem)
{
/* The following operations must be performed with interrupts
* disabled because sem_post() may be called from an interrupt
* handler.
*/
saved_state = irqsave();
/* Any further errors could only be occurred because the semaphore
* is not available.
*/
*get_errno_ptr() = EAGAIN;
/* If the semaphore is available, give it to the requesting task */
if (sem->semcount > 0)
{
/* It is, let the task take the semaphore */
sem->semcount--;
rtcb->waitsem = NULL;
ret = OK;
}
/* Interrupts may now be enabled. */
irqrestore(saved_state);
}
return ret;
}
