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