nuttx/libs/libc/semaphore/sem_setprotocol.c

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/****************************************************************************
* libs/libc/semaphore/sem_setprotocol.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 <assert.h>
#include <errno.h>
#include <nuttx/semaphore.h>
#ifndef CONFIG_PRIORITY_INHERITANCE
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: nxsem_set_protocol
*
* Description:
* Set semaphore protocol attribute.
*
2019-09-08 23:59:14 +02:00
* One particularly important use of this function is when a semaphore
* is used for inter-task communication like:
*
* TASK A TASK B
* nxsem_init(sem, 0, 0);
* nxsem_wait(sem);
* nxsem_post(sem);
* Awakens as holder
*
* In this case priority inheritance can interfere with the operation of
* the semaphore. The problem is that when TASK A is restarted it is a
* holder of the semaphore. However, it never calls nxsem_post(sem) so it
* becomes *permanently* a holder of the semaphore and may have its
* priority boosted when any other task tries to acquire the semaphore.
*
* The fix is to call nxsem_set_protocol(SEM_PRIO_NONE) immediately after
* the sem_init() call so that there will be no priority inheritance
* operations on this semaphore.
*
* Input Parameters:
* sem - A pointer to the semaphore whose attributes are to be
* modified
* protocol - The new protocol to use
*
* Returned Value:
* This function is exposed as a non-standard application interface. It
* returns zero (OK) if successful. Otherwise, -EINVAL is returned if the
* value specified by protocol is invalid or -ENOTSUP if the value
* specified by protocol is an unsupported value.
*
****************************************************************************/
int nxsem_set_protocol(FAR sem_t *sem, int protocol)
{
DEBUGASSERT(sem != NULL);
switch (protocol)
{
case SEM_PRIO_NONE:
return OK;
case SEM_PRIO_INHERIT:
case SEM_PRIO_PROTECT:
return -ENOTSUP;
default:
break;
}
return -EINVAL;
}
/****************************************************************************
* Name: sem_setprotocol
*
* Description:
* Set semaphore protocol attribute.
*
2019-09-08 23:59:14 +02:00
* One particularly important use of this function is when a semaphore
* is used for inter-task communication like:
*
* TASK A TASK B
* sem_init(sem, 0, 0);
* sem_wait(sem);
* sem_post(sem);
* Awakens as holder
*
* In this case priority inheritance can interfere with the operation of
* the semaphore. The problem is that when TASK A is restarted it is a
* holder of the semaphore. However, it never calls sem_post(sem) so it
* becomes *permanently* a holder of the semaphore and may have its
* priority boosted when any other task tries to acquire the semaphore.
*
* The fix is to call sem_setprotocol(SEM_PRIO_NONE) immediately after
* the sem_init() call so that there will be no priority inheritance
* operations on this semaphore.
*
* Input Parameters:
* sem - A pointer to the semaphore whose attributes are to be
* modified
* protocol - The new protocol to use
*
* Returned Value:
* This function is exposed as a non-standard application interface. It
* returns zero (OK) if successful. Otherwise, -1 (ERROR) is returned and
* the errno value is set appropriately.
*
****************************************************************************/
int sem_setprotocol(FAR sem_t *sem, int protocol)
{
int ret;
ret = nxsem_set_protocol(sem, protocol);
if (ret < 0)
{
set_errno(-ret);
ret = ERROR;
}
return ret;
}
#endif /* !CONFIG_PRIORITY_INHERITANCE */