250 lines
8.2 KiB
C
250 lines
8.2 KiB
C
/****************************************************************************
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* include/semaphore.h
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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#ifndef __INCLUDE_SEMAPHORE_H
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#define __INCLUDE_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 <stdint.h>
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#include <limits.h>
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#include <time.h>
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#include <nuttx/queue.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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/* Value returned by sem_open() in the event of a failure. */
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#define SEM_FAILED NULL
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/* Bit definitions for the struct sem_s flags field */
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#define PRIOINHERIT_FLAGS_ENABLE (1 << 0) /* Bit 0: Priority inheritance
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* is enabled for this semaphore. */
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#define PRIOINHERIT_FLAGS_DISABLE (0 << 0) /* Bit 0: Priority inheritance
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* is disabled for this semaphore. */
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/****************************************************************************
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* Public Type Declarations
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****************************************************************************/
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/* This structure contains information about the holder of a semaphore */
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#ifdef CONFIG_PRIORITY_INHERITANCE
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struct tcb_s; /* Forward reference */
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struct sem_s;
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struct semholder_s
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{
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#if CONFIG_SEM_PREALLOCHOLDERS > 0
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FAR struct semholder_s *flink; /* List of semaphore's holder */
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#endif
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FAR struct semholder_s *tlink; /* List of task held semaphores */
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FAR struct sem_s *sem; /* Ths corresponding semaphore */
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FAR struct tcb_s *htcb; /* Ths corresponding TCB */
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int16_t counts; /* Number of counts owned by this holder */
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};
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#if CONFIG_SEM_PREALLOCHOLDERS > 0
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# define SEMHOLDER_INITIALIZER {NULL, NULL, NULL, NULL, 0}
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# define INITIALIZE_SEMHOLDER(h) \
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do { \
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(h)->flink = NULL; \
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(h)->tlink = NULL; \
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(h)->sem = NULL; \
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(h)->htcb = NULL; \
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(h)->counts = 0; \
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} while (0)
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#else
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# define SEMHOLDER_INITIALIZER {NULL, NULL, NULL, 0}
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# define INITIALIZE_SEMHOLDER(h) \
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do { \
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(h)->tlink = NULL; \
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(h)->sem = NULL; \
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(h)->htcb = NULL; \
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(h)->counts = 0; \
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} while (0)
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#endif
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#endif /* CONFIG_PRIORITY_INHERITANCE */
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#define SEM_WAITLIST_INITIALIZER {NULL, NULL}
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/* This is the generic semaphore structure. */
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struct sem_s
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{
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volatile int16_t semcount; /* >0 -> Num counts available */
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/* <0 -> Num tasks waiting for semaphore */
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dq_queue_t waitlist;
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/* If priority inheritance is enabled, then we have to keep track of which
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* tasks hold references to the semaphore.
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*/
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#ifdef CONFIG_PRIORITY_INHERITANCE
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uint8_t flags; /* See PRIOINHERIT_FLAGS_* definitions */
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# if CONFIG_SEM_PREALLOCHOLDERS > 0
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FAR struct semholder_s *hhead; /* List of holders of semaphore counts */
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# else
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struct semholder_s holder[2]; /* Slot for old and new holder */
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# endif
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#endif
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};
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typedef struct sem_s sem_t;
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/* Initializers */
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#ifdef CONFIG_PRIORITY_INHERITANCE
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# if CONFIG_SEM_PREALLOCHOLDERS > 0
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/* semcount, waitlist, flags, hhead */
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# define SEM_INITIALIZER(c) \
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{(c), SEM_WAITLIST_INITIALIZER, 0, NULL}
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# else
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/* semcount, waitlist, flags, holder[2] */
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# define SEM_INITIALIZER(c) \
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{(c), SEM_WAITLIST_INITIALIZER, 0, {SEMHOLDER_INITIALIZER, SEMHOLDER_INITIALIZER}}
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# endif
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#else
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/* semcount, waitlist */
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# define SEM_INITIALIZER(c) \
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{(c), SEM_WAITLIST_INITIALIZER}
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#endif
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# define SEM_WAITLIST(sem) (&((sem)->waitlist))
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/****************************************************************************
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* Public Data
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****************************************************************************/
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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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/* Counting Semaphore Interfaces (based on POSIX APIs) */
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int sem_init(FAR sem_t *sem, int pshared, unsigned int value);
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int sem_destroy(FAR sem_t *sem);
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int sem_wait(FAR sem_t *sem);
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int sem_timedwait(FAR sem_t *sem, FAR const struct timespec *abstime);
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int sem_clockwait(FAR sem_t *sem, clockid_t clockid,
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FAR const struct timespec *abstime);
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int sem_trywait(FAR sem_t *sem);
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int sem_post(FAR sem_t *sem);
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int sem_getvalue(FAR sem_t *sem, FAR int *sval);
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#ifdef CONFIG_FS_NAMED_SEMAPHORES
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FAR sem_t *sem_open(FAR const char *name, int oflag, ...);
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int sem_close(FAR sem_t *sem);
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int sem_unlink(FAR const char *name);
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#endif
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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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* Input 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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* Returned Value:
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* This function is exposed as a non-standard application interface. It
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* returns zero (OK) if successful. Otherwise, -1 (ERROR) is returned and
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* the errno value is set 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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/****************************************************************************
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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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* Input 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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* Returned Value:
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* This function is exposed as a non-standard application interface. It
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* returns zero (OK) if successful. Otherwise, -1 (ERROR) is returned and
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* the errno value is set 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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#undef EXTERN
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#ifdef __cplusplus
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}
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#endif
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#endif /* __INCLUDE_SEMAPHORE_H */
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