forked from Archive/PX4-Autopilot
138 lines
4.8 KiB
C
138 lines
4.8 KiB
C
/****************************************************************************
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* sched/pthread_condsignal.c
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*
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* Copyright (C) 2007-2009, 2012 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 <pthread.h>
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#include <errno.h>
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#include <debug.h>
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#include "pthread_internal.h"
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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: pthread_cond_signal
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*
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* Description:
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* A thread can signal on a condition variable.
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*
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* Parameters:
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* None
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*
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* Return Value:
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* None
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*
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* Assumptions:
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*
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****************************************************************************/
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int pthread_cond_signal(FAR pthread_cond_t *cond)
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{
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int ret = OK;
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int sval;
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sdbg("cond=0x%p\n", cond);
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if (!cond)
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{
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ret = EINVAL;
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}
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else
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{
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/* Get the current value of the semaphore */
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if (sem_getvalue((sem_t*)&cond->sem, &sval) != OK)
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{
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ret = EINVAL;
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}
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/* If the value is less than zero (meaning that one or more
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* thread is waiting), then post the condition semaphore.
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* Only the highest priority waiting thread will get to execute
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*/
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else
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{
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/* One of my objectives in this design was to make pthread_cond_signal
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* usable from interrupt handlers. However, from interrupt handlers,
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* you cannot take the associated mutex before signaling the condition.
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* As a result, I think that there could be a race condition with
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* the following logic which assumes that the if sval < 0 then the
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* thread is waiting. Without the mutex, there is no atomic, protected
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* operation that will guarantee this to be so.
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*/
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sdbg("sval=%d\n", sval);
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if (sval < 0)
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{
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sdbg("Signalling...\n");
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ret = pthread_givesemaphore((sem_t*)&cond->sem);
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}
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}
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}
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sdbg("Returning %d\n", ret);
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return ret;
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}
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