aab0d08d21
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@54 42af7a65-404d-4744-a932-0658087f49c3
146 lines
4.8 KiB
C
146 lines
4.8 KiB
C
/************************************************************
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* sem_trywait.c
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*
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* Copyright (C) 2007 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
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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 Gregory Nutt 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 <sys/types.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/arch.h>
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#include "os_internal.h"
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#include "sem_internal.h"
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/************************************************************
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* Compilation Switches
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************************************************************/
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/************************************************************
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* Definitions
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************************************************************/
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/************************************************************
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* Private Type Declarations
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************************************************************/
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/************************************************************
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* Global Variables
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************************************************************/
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/************************************************************
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* Private Variables
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************************************************************/
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/************************************************************
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* Private Functions
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************************************************************/
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/************************************************************
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* Public Functions
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************************************************************/
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/************************************************************
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* Function: sem_trywait
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*
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* Description:
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* This function locks the specified semaphore only if the
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* semaphore is currently not locked. Otherwise, it locks
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* the semaphore. In either case, the call returns without
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* 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
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* If this function returns -1 (ERROR), then the cause
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* of the failure will be reported in "errno" as:
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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(sem_t *sem)
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{
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_TCB *rtcb = (_TCB*)g_readytorun.head;
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irqstate_t saved_state;
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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())
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/* Assume any errors reported are due to invalid arguments. */
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*get_errno_ptr() = EINVAL;
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if (sem)
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{
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/* The following operations must be performed with interrupts
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* disabled because sem_post() may be called from an interrupt
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* handler.
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*/
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saved_state = irqsave();
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/* Any further errors could only be occurred because the semaphore
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* is not available.
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*/
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*get_errno_ptr() = 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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irqrestore(saved_state);
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}
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return ret;
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}
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