incubator-nuttx/include/nuttx/semaphore.h

210 lines
7.4 KiB
C

/****************************************************************************
* include/nuttx/semaphore.h
*
* Copyright (C) 2014-2016 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.
*
****************************************************************************/
#ifndef __INCLUDE_NUTTX_SEMAPHORE_H
#define __INCLUDE_NUTTX_SEMAPHORE_H
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <semaphore.h>
#include <nuttx/clock.h>
#include <nuttx/fs/fs.h>
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* Values for protocol attribute */
#define SEM_PRIO_NONE 0
#define SEM_PRIO_INHERIT 1
#define SEM_PRIO_PROTECT 2
/****************************************************************************
* Public Type Definitions
****************************************************************************/
#ifdef CONFIG_FS_NAMED_SEMAPHORES
/* This is the named semaphore inode */
struct inode;
struct nsem_inode_s
{
/* This must be the first element of the structure. In sem_close() this
* structure must be cast compatible with sem_t.
*/
sem_t ns_sem; /* The contained semaphore */
/* Inode payload unique to named semaphores. */
FAR struct inode *ns_inode; /* Containing inode */
};
#endif
/****************************************************************************
* Public Data
****************************************************************************/
#ifndef __ASSEMBLY__
#ifdef __cplusplus
#define EXTERN extern "C"
extern "C"
{
#else
#define EXTERN extern
#endif
/****************************************************************************
* Public Function Prototypes
****************************************************************************/
/****************************************************************************
* Name: sem_tickwait
*
* Description:
* This function is a lighter weight version of sem_timedwait(). It is
* non-standard and intended only for use within the RTOS.
*
* Parameters:
* sem - Semaphore object
* start - The system time that the delay is relative to. If the
* current time is not the same as the start time, then the
* delay will be adjust so that the end time will be the same
* in any event.
* delay - Ticks to wait from the start time until the semaphore is
* posted. If ticks is zero, then this function is equivalent
* to sem_trywait().
*
* Return Value:
* Zero (OK) is returned on success. A negated errno value is returned on
* failure. -ETIMEDOUT is returned on the timeout condition.
*
****************************************************************************/
int sem_tickwait(FAR sem_t *sem, systime_t start, uint32_t delay);
/****************************************************************************
* Name: sem_reset
*
* Description:
* Reset a semaphore count to a specific value. This is similar to part
* of the operation of sem_init(). But sem_reset() may need to wake up
* tasks waiting on a count. This kind of operation is sometimes required
* within the OS (only) for certain error handling conditions.
*
* Parameters:
* sem - Semaphore descriptor to be reset
* count - The requested semaphore count
*
* Return Value:
* 0 (OK) or a negated errno value if unsuccessful
*
****************************************************************************/
int sem_reset(FAR sem_t *sem, int16_t count);
/****************************************************************************
* Function: sem_getprotocol
*
* Description:
* Return the value of the semaphore protocol attribute.
*
* Parameters:
* sem - A pointer to the semaphore whose attributes are to be
* queried.
* protocol - The user provided location in which to store the protocol
* value.
*
* Return Value:
* 0 if successful. Otherwise, -1 is returned and the errno value is set
* appropriately.
*
****************************************************************************/
int sem_getprotocol(FAR sem_t *sem, FAR int *protocol);
/****************************************************************************
* Function: sem_setprotocol
*
* Description:
* Set semaphore protocol attribute.
*
* 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.
*
* Parameters:
* sem - A pointer to the semaphore whose attributes are to be
* modified
* protocol - The new protocol to use
*
* Return Value:
* 0 if successful. Otherwise, -1 is returned and the errno value is set
* appropriately.
*
****************************************************************************/
int sem_setprotocol(FAR sem_t *sem, int protocol);
#undef EXTERN
#ifdef __cplusplus
}
#endif
#endif /* __ASSEMBLY__ */
#endif /* __INCLUDE_NUTTX_SEMAPHORE_H */