nuttx/sched/semaphore/sem_post.c

233 lines
7.4 KiB
C

/****************************************************************************
* sched/semaphore/sem_post.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <limits.h>
#include <errno.h>
#include <sched.h>
#include <nuttx/irq.h>
#include <nuttx/arch.h>
#include "sched/sched.h"
#include "semaphore/semaphore.h"
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: nxsem_post
*
* Description:
* When a kernel thread has finished with a semaphore, it will call
* nxsem_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 nxsem_wait().
*
* Input Parameters:
* sem - Semaphore descriptor
*
* Returned Value:
* This is an internal OS interface and should not be used by applications.
* It follows the NuttX internal error return policy: Zero (OK) is
* returned on success. A negated errno value is returned on failure.
*
* Assumptions:
* This function may be called from an interrupt handler.
*
****************************************************************************/
int nxsem_post(FAR sem_t *sem)
{
FAR struct tcb_s *stcb = NULL;
irqstate_t flags;
int16_t sem_count;
int ret = -EINVAL;
/* Make sure we were supplied with a valid semaphore. */
if (sem != NULL)
{
/* The following operations must be performed with interrupts
* disabled because sem_post() may be called from an interrupt
* handler.
*/
flags = enter_critical_section();
sem_count = sem->semcount;
/* Check the maximum allowable value */
if (sem_count >= SEM_VALUE_MAX)
{
leave_critical_section(flags);
return -EOVERFLOW;
}
/* Perform the semaphore unlock operation, releasing this task as a
* holder then also incrementing the count on the semaphore.
*
* NOTE: When semaphores are used for signaling purposes, the holder
* of the semaphore may not be this thread! In this case,
* nxsem_release_holder() will do nothing.
*
* In the case of a mutex this could be simply resolved since there is
* only one holder but for the case of counting semaphores, there may
* be many holders and if the holder is not this thread, then it is
* not possible to know which thread/holder should be released.
*
* For this reason, it is recommended that priority inheritance be
* disabled via nxsem_set_protocol(SEM_PRIO_NONE) when the semaphore is
* initialized if the semaphore is to used for signaling purposes.
*/
nxsem_release_holder(sem);
sem_count++;
sem->semcount = sem_count;
#ifdef CONFIG_PRIORITY_INHERITANCE
/* Don't let any unblocked tasks run until we complete any priority
* restoration steps. Interrupts are disabled, but we do not want
* the head of the ready-to-run list to be modified yet.
*
* NOTE: If this sched_lock is called from an interrupt handler, it
* will do nothing.
*/
sched_lock();
#endif
/* If the result of semaphore unlock is non-positive, then
* there must be some task waiting for the semaphore.
*/
if (sem_count <= 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 struct tcb_s *)g_waitingforsemaphore.head;
(stcb && stcb->waitobj != sem);
stcb = stcb->flink);
if (stcb != NULL)
{
/* The task will be the new holder of the semaphore when
* it is awakened.
*/
nxsem_add_holder_tcb(stcb, sem);
/* Stop the watchdog timer */
wd_cancel(&stcb->waitdog);
/* Restart the waiting task. */
up_unblock_task(stcb);
}
#if 0 /* REVISIT: This can fire on IOB throttle semaphore */
else
{
/* This should not happen. */
DEBUGPANIC();
}
#endif
}
/* Check if we need to drop the priority of any threads holding
* this semaphore. The priority could have been boosted while they
* held the semaphore.
*/
#ifdef CONFIG_PRIORITY_INHERITANCE
nxsem_restore_baseprio(stcb, sem);
sched_unlock();
#endif
ret = OK;
/* Interrupts may now be enabled. */
leave_critical_section(flags);
}
return ret;
}
/****************************************************************************
* Name: 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 nxsem_wait().
*
* Input Parameters:
* sem - Semaphore descriptor
*
* Returned Value:
* This function is a standard, POSIX application interface. It will
* return zero (OK) if successful. Otherwise, -1 (ERROR) is returned and
* the errno value is set appropriately.
*
* Assumptions:
* This function may be called from an interrupt handler.
*
****************************************************************************/
int sem_post(FAR sem_t *sem)
{
int ret;
ret = nxsem_post(sem);
if (ret < 0)
{
set_errno(-ret);
ret = ERROR;
}
return ret;
}