210 lines
7.3 KiB
C
210 lines
7.3 KiB
C
/****************************************************************************
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* include/nuttx/semaphore.h
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*
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* Copyright (C) 2014-2016 Gregory Nutt. All rights 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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#ifndef __INCLUDE_NUTTX_SEMAPHORE_H
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#define __INCLUDE_NUTTX_SEMAPHORE_H
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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 <semaphore.h>
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#include <nuttx/clock.h>
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#include <nuttx/fs/fs.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/* Values for protocol attribute */
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#define SEM_PRIO_NONE 0
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#define SEM_PRIO_INHERIT 1
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#define SEM_PRIO_PROTECT 2
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/****************************************************************************
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* Public Type Definitions
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****************************************************************************/
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#ifdef CONFIG_FS_NAMED_SEMAPHORES
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/* This is the named semaphore inode */
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struct inode;
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struct nsem_inode_s
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{
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/* This must be the first element of the structure. In sem_close() this
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* structure must be cast compatible with sem_t.
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*/
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sem_t ns_sem; /* The contained semaphore */
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/* Inode payload unique to named semaphores. */
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FAR struct inode *ns_inode; /* Containing inode */
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};
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#endif
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/****************************************************************************
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* Public Data
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****************************************************************************/
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#ifndef __ASSEMBLY__
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#ifdef __cplusplus
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#define EXTERN extern "C"
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extern "C"
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{
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#else
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#define EXTERN extern
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#endif
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/****************************************************************************
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* Public Function Prototypes
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****************************************************************************/
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/****************************************************************************
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* Name: sem_tickwait
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*
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* Description:
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* This function is a lighter weight version of sem_timedwait(). It is
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* non-standard and intended only for use within the RTOS.
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*
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* Parameters:
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* sem - Semaphore object
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* start - The system time that the delay is relative to. If the
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* current time is not the same as the start time, then the
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* delay will be adjust so that the end time will be the same
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* in any event.
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* delay - Ticks to wait from the start time until the semaphore is
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* posted. If ticks is zero, then this function is equivalent
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* to sem_trywait().
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*
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* Return Value:
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* Zero (OK) is returned on success. A negated errno value is returned on
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* failure. -ETIMEDOUT is returned on the timeout condition.
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*
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****************************************************************************/
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int sem_tickwait(FAR sem_t *sem, systime_t start, uint32_t delay);
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/****************************************************************************
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* Name: sem_reset
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*
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* Description:
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* Reset a semaphore count to a specific value. This is similar to part
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* of the operation of sem_init(). But sem_reset() may need to wake up
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* tasks waiting on a count. This kind of operation is sometimes required
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* within the OS (only) for certain error handling conditions.
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*
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* Parameters:
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* sem - Semaphore descriptor to be reset
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* count - The requested semaphore count
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*
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* Return Value:
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* 0 (OK) or a negated errno value if unsuccessful
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*
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****************************************************************************/
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int sem_reset(FAR sem_t *sem, int16_t count);
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/****************************************************************************
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* Name: sem_getprotocol
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*
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* Description:
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* Return the value of the semaphore protocol attribute.
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*
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* Parameters:
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* sem - A pointer to the semaphore whose attributes are to be
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* queried.
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* protocol - The user provided location in which to store the protocol
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* value.
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*
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* Return Value:
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* 0 if successful. Otherwise, -1 is returned and the errno value is set
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* appropriately.
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*
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****************************************************************************/
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int sem_getprotocol(FAR sem_t *sem, FAR int *protocol);
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/****************************************************************************
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* Name: sem_setprotocol
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*
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* Description:
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* Set semaphore protocol attribute.
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*
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* One particularly important use of this function is when a semaphore
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* is used for inter-task communication like:
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*
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* TASK A TASK B
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* sem_init(sem, 0, 0);
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* sem_wait(sem);
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* sem_post(sem);
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* Awakens as holder
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*
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* In this case priority inheritance can interfere with the operation of
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* the semaphore. The problem is that when TASK A is restarted it is a
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* holder of the semaphore. However, it never calls sem_post(sem) so it
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* becomes *permanently* a holder of the semaphore and may have its
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* priority boosted when any other task tries to acquire the semaphore.
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*
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* The fix is to call sem_setprotocol(SEM_PRIO_NONE) immediately after
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* the sem_init() call so that there will be no priority inheritance
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* operations on this semaphore.
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*
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* Parameters:
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* sem - A pointer to the semaphore whose attributes are to be
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* modified
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* protocol - The new protocol to use
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*
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* Return Value:
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* 0 if successful. Otherwise, -1 is returned and the errno value is set
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* appropriately.
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*
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****************************************************************************/
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int sem_setprotocol(FAR sem_t *sem, int protocol);
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#undef EXTERN
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#ifdef __cplusplus
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}
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#endif
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#endif /* __ASSEMBLY__ */
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#endif /* __INCLUDE_NUTTX_SEMAPHORE_H */
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