125 lines
4.1 KiB
C
125 lines
4.1 KiB
C
/****************************************************************************
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* sched/semaphore/sem_trywait.c
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*
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* Copyright (C) 2007-2009, 2016 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <stdbool.h>
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#include <semaphore.h>
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#include <sched.h>
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#include <errno.h>
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#include <nuttx/irq.h>
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#include <nuttx/arch.h>
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#include "sched/sched.h"
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#include "semaphore/semaphore.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: sem_trywait
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*
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* Description:
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* This function locks the specified semaphore only if the semaphore is
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* currently not locked. Otherwise, it locks the semaphore. In either
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* case, the call returns without blocking.
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*
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* Parameters:
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* sem - the semaphore descriptor
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*
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* Return Value:
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* 0 (OK) or -1 (ERROR) if unsuccessful. If this function returns -1
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* (ERROR),then the cause of the failure will be reported in "errno" as:
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*
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* EINVAL: Invalid attempt to get the semaphore
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* EAGAIN: The semaphore is not available.
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*
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* Assumptions:
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*
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****************************************************************************/
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int sem_trywait(FAR sem_t *sem)
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{
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FAR struct tcb_s *rtcb = this_task();
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irqstate_t flags;
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int ret = ERROR;
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/* This API should not be called from interrupt handlers */
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DEBUGASSERT(up_interrupt_context() == false);
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/* Assume any errors reported are due to invalid arguments. */
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set_errno(EINVAL);
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if (sem)
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{
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/* The following operations must be performed with interrupts disabled
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* because sem_post() may be called from an interrupt handler.
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*/
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flags = enter_critical_section();
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/* Any further errors could only occurr because the semaphore is not
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* available.
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*/
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set_errno(EAGAIN);
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/* If the semaphore is available, give it to the requesting task */
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if (sem->semcount > 0)
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{
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/* It is, let the task take the semaphore */
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sem->semcount--;
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rtcb->waitsem = NULL;
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ret = OK;
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}
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/* Interrupts may now be enabled. */
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leave_critical_section(flags);
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}
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return ret;
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}
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