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142 lines
4.9 KiB
142 lines
4.9 KiB
/**************************************************************************** |
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* sched/sem_trywait.c |
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* |
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* Copyright (C) 2007-2009 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/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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* Pre-processor 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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* 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 _TCB *rtcb = (FAR _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() == 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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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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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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irqrestore(saved_state); |
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} |
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return ret; |
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}
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