/************************************************************
* sem_post.c
*
* Copyright (C) 2007 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* 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 Gregory Nutt 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
* POSSIBILITY OF SUCH DAMAGE.
*
************************************************************/
/************************************************************
* Included Files
************************************************************/
#include <sys/types.h>
#include <semaphore.h>
#include <sched.h>
#include <nuttx/arch.h>
#include "os_internal.h"
#include "sem_internal.h"
/************************************************************
* Compilation Switches
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/************************************************************
* Definitions
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/************************************************************
* Private Type Declarations
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/************************************************************
* Global Variables
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/************************************************************
* Private Variables
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/************************************************************
* Private Functions
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/************************************************************
* Public Functions
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/************************************************************
* Function: sem_post
*
* Description:
* When a task has finished with a semaphore, it will call
* sem_post(). This function unlocks the semaphore
* referenced by sem by performing the semaphore unlock
* operation on that semaphore.
*
* If the semaphore value resulting from this operation
* is positive, then no tasks were blocked waiting for the
* semaphore to become unlocked; the semaphore is simply
* incremented.
*
* If the value of the semaphore resulting from this
* operation is zero, then one of the tasks blocked
* waiting for the semaphore shall be allowed to return
* successfully from its call to sem_wait().
*
* Parameters:
* sem - Semaphore descriptor
*
* Return Value:
* 0 (OK) or -1 (ERROR) if unsuccessful
*
* Assumptions:
* This function cannot be called from an interrupt handler.
* It assumes the currently executing task is the one that
* is performing the unlock.
*
************************************************************/
int sem_post(sem_t *sem)
{
FAR _TCB *stcb;
STATUS ret = ERROR;
irqstate_t saved_state;
/* Make sure we were supplied with a valid semaphore. */
if (sem)
{
/* The following operations must be performed with interrupts
* disabled because sem_post() may be called from an interrupt
* handler.
*/
saved_state = irqsave();
/* Perform the semaphore unlock operation. */
ASSERT(sem->semcount < SEM_MAX_VALUE);
sem->semcount++;
/* If the result of of semaphore unlock is non-positive, then
* there must be some task waiting for the semaphore.
*/
if (sem->semcount <= 0)
{
/* Check if there are any tasks in the waiting for semaphore
* task list that are waiting for this semaphore. This is a
* prioritized list so the first one we encounter is the one
* that we want.
*/
for (stcb = (FAR _TCB*)g_waitingforsemaphore.head;
((stcb) && (stcb->waitsem != sem));
stcb = stcb->flink);
if (stcb)
{
/* It is, let the task take the semaphore */
stcb->waitsem = NULL;
/* Restart the waiting task. */
up_unblock_task(stcb);
}
}
ret = OK;
/* Interrupts may now be enabled. */
irqrestore(saved_state);
}
return ret;
}
