239 lines
8.1 KiB
C
239 lines
8.1 KiB
C
/****************************************************************************
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* sched/semaphore/sem_post.c
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*
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* Copyright (C) 2007-2009, 2012-2013, 2016-2017 Gregory Nutt. All rights
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* 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 <limits.h>
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#include <semaphore.h>
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#include <errno.h>
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#include <sched.h>
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#include <nuttx/irq.h>
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#include <nuttx/arch.h>
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#include "sched/sched.h"
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#include "semaphore/semaphore.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: nxsem_post
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*
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* Description:
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* When a kernel thread has finished with a semaphore, it will call
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* nxsem_post(). This function unlocks the semaphore referenced by sem
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* by performing the semaphore unlock operation on that semaphore.
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*
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* If the semaphore value resulting from this operation is positive, then
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* no tasks were blocked waiting for the semaphore to become unlocked; the
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* semaphore is simply incremented.
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*
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* If the value of the semaphore resulting from this operation is zero,
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* then one of the tasks blocked waiting for the semaphore shall be
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* allowed to return successfully from its call to nxsem_wait().
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*
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* Input Parameters:
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* sem - Semaphore descriptor
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*
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* Returned Value:
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* This is an internal OS interface and should not be used by applications.
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* It follows the NuttX internal error return policy: Zero (OK) is
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* returned on success. A negated errno value is returned on failure.
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*
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* Assumptions:
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* This function may be called from an interrupt handler.
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*
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****************************************************************************/
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int nxsem_post(FAR sem_t *sem)
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{
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FAR struct tcb_s *stcb = NULL;
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irqstate_t flags;
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int ret = -EINVAL;
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/* Make sure we were supplied with a valid semaphore. */
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if (sem != NULL)
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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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flags = enter_critical_section();
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/* Perform the semaphore unlock operation, releasing this task as a
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* holder then also incrementing the count on the semaphore.
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*
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* NOTE: When semaphores are used for signaling purposes, the holder
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* of the semaphore may not be this thread! In this case,
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* nxsem_releaseholder() will do nothing.
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*
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* In the case of a mutex this could be simply resolved since there is
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* only one holder but for the case of counting semaphores, there may
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* be many holders and if the holder is not this thread, then it is
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* not possible to know which thread/holder should be released.
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*
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* For this reason, it is recommended that priority inheritance be
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* disabled via nxsem_setprotocol(SEM_PRIO_NONE) when the semaphore is
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* initialized if the semaphore is to used for signaling purposes.
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*/
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DEBUGASSERT(sem->semcount < SEM_VALUE_MAX);
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nxsem_releaseholder(sem);
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sem->semcount++;
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#ifdef CONFIG_PRIORITY_INHERITANCE
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/* Don't let any unblocked tasks run until we complete any priority
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* restoration steps. Interrupts are disabled, but we do not want
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* the head of the read-to-run list to be modified yet.
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*
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* NOTE: If this sched_lock is called from an interrupt handler, it
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* will do nothing.
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*/
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sched_lock();
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#endif
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/* If the result of of semaphore unlock is non-positive, then
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* there must be some task waiting for the semaphore.
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*/
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if (sem->semcount <= 0)
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{
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/* Check if there are any tasks in the waiting for semaphore
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* task list that are waiting for this semaphore. This is a
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* prioritized list so the first one we encounter is the one
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* that we want.
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*/
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for (stcb = (FAR struct tcb_s *)g_waitingforsemaphore.head;
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(stcb && stcb->waitsem != sem);
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stcb = stcb->flink);
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if (stcb != NULL)
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{
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/* The task will be the new holder of the semaphore when
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* it is awakened.
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*/
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nxsem_addholder_tcb(stcb, sem);
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/* It is, let the task take the semaphore */
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stcb->waitsem = NULL;
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/* Restart the waiting task. */
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up_unblock_task(stcb);
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}
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#if 0 /* REVISIT: This can fire on IOB throttle semaphore */
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else
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{
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/* This should not happen. */
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DEBUGPANIC();
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}
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#endif
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}
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/* Check if we need to drop the priority of any threads holding
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* this semaphore. The priority could have been boosted while they
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* held the semaphore.
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*/
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#ifdef CONFIG_PRIORITY_INHERITANCE
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nxsem_restorebaseprio(stcb, sem);
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sched_unlock();
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#endif
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ret = OK;
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/* Interrupts may now be enabled. */
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leave_critical_section(flags);
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}
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return ret;
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}
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/****************************************************************************
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* Name: sem_post
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*
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* Description:
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* When a task has finished with a semaphore, it will call sem_post().
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* This function unlocks the semaphore referenced by sem by performing the
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* semaphore unlock operation on that semaphore.
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*
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* If the semaphore value resulting from this operation is positive, then
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* no tasks were blocked waiting for the semaphore to become unlocked; the
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* semaphore is simply incremented.
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*
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* If the value of the semaphore resulting from this operation is zero,
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* then one of the tasks blocked waiting for the semaphore shall be
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* allowed to return successfully from its call to nxsem_wait().
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*
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* Input Parameters:
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* sem - Semaphore descriptor
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*
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* Returned Value:
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* This function is a standard, POSIX application interface. It will
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* return zero (OK) if successful. Otherwise, -1 (ERROR) is returned and
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* the errno value is set appropriately.
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*
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* Assumptions:
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* This function may be called from an interrupt handler.
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*
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****************************************************************************/
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int sem_post(FAR sem_t *sem)
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{
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int ret;
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ret = nxsem_post(sem);
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if (ret < 0)
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{
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set_errno(-ret);
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ret = ERROR;
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}
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return ret;
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}
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