incubator-nuttx/libc/semaphore/sem_setprotocol.c

163 lines
5.7 KiB
C

/****************************************************************************
* libc/semaphore/sem_setprotocol.c
*
* Copyright (C) 2016-2017 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
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <assert.h>
#include <errno.h>
#include <nuttx/semaphore.h>
#ifndef CONFIG_PRIORITY_INHERITANCE
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: nxsem_setprotocol
*
* Description:
* Set semaphore protocol attribute.
*
* One particularly important use of this furnction is when a semaphore
* is used for inter-task communication like:
*
* TASK A TASK B
* nxsem_init(sem, 0, 0);
* nxsem_wait(sem);
* snxem_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_setprotocol(SEM_PRIO_NONE) immediately after
* the sem_init() call so that there will be no priority inheritance
* operations on this semaphore.
*
* 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 nxsem_setprotocol(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 -ENOSYS;
break;
default:
break;
}
return -EINVAL;
}
/****************************************************************************
* Name: sem_setprotocol
*
* Description:
* Set semaphore protocol attribute.
*
* One particularly important use of this furnction 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.
*
* 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_setprotocol(sem, protocol);
if (ret < 0)
{
set_errno(-ret);
ret = ERROR;
}
return ret;
}
#endif /* !CONFIG_PRIORITY_INHERITANCE */