semaphore.h

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/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed 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
 *
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 * 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.
 *
 ****************************************************************************/
/****************************************************************************
 * include/semaphore.h
 *
 *   Copyright (C) 2007-2009, 2012-2013 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
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 ****************************************************************************/

#ifndef __INCLUDE_SEMAPHORE_H
#define __INCLUDE_SEMAPHORE_H

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/config.h>

#include <stdint.h>
#include <limits.h>

#ifdef __cplusplus
#define EXTERN extern "C"
extern "C" {
#else
#define EXTERN extern
#endif

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/****************************************************************************
 * Public Type Declarations
 ****************************************************************************/

/* This structure contains information about the holder of a semaphore */

#ifdef CONFIG_PRIORITY_INHERITANCE
struct tcb_s;                   /* Forward reference */
struct semholder_s {
#if CONFIG_SEM_PREALLOCHOLDERS > 0
    struct semholder_s *flink;  /* Implements singly linked list */
#endif
    FAR struct tcb_s *htcb;     /* Holder TCB */
    int16_t counts;             /* Number of counts owned by this holder */
};

#if CONFIG_SEM_PREALLOCHOLDERS > 0
#define SEMHOLDER_INITIALIZER {NULL, NULL, 0}
#else
#define SEMHOLDER_INITIALIZER {NULL, 0}
#endif
#endif                          /* CONFIG_PRIORITY_INHERITANCE */

struct sem_s {
    int16_t semcount;           /* >0 -> Num counts available */
    /* <0 -> Num tasks waiting for semaphore */
    /* If priority inheritance is enabled, then we have to keep track of which
     * tasks hold references to the semaphore.
     */

#ifdef CONFIG_PRIORITY_INHERITANCE
#if CONFIG_SEM_PREALLOCHOLDERS > 0
    FAR struct semholder_s *hhead;  /* List of holders of semaphore counts */
#else
    struct semholder_s holder;  /* Single holder */
#endif
#endif
};

typedef struct sem_s sem_t;

/* Initializers */
#ifdef CONFIG_PRIORITY_INHERITANCE
#if CONFIG_SEM_PREALLOCHOLDERS > 0
#define SEM_INITIALIZER(c) {(c), NULL}  /* semcount, hhead */
#else
#define SEM_INITIALIZER(c) {(c), SEMHOLDER_INITIALIZER} /* semcount, holder */
#endif
#else
#define SEM_INITIALIZER(c) {(c)}    /* semcount */
#endif

/****************************************************************************
 * Public Variables
 ****************************************************************************/

/****************************************************************************
 * Public Function Prototypes
 ****************************************************************************/
/* Forward references needed by some prototypes */

struct timespec;                /* Defined in time.h */

/* Counting Semaphore Interfaces (based on POSIX APIs) */
int sem_init(FAR sem_t *sem, int pshared, unsigned int value);

int sem_destroy(FAR sem_t *sem);
int sem_wait(FAR sem_t *sem);
int sem_timedwait(FAR sem_t *sem, FAR const struct timespec *abstime);
int sem_trywait(FAR sem_t *sem);
int sem_post(FAR sem_t *sem);
int sem_getvalue(FAR sem_t *sem, FAR int *sval);

#ifdef CONFIG_FS_NAMED_SEMAPHORES

FAR sem_t *sem_open(FAR const char *name, int oflag, ...);
int sem_close(FAR sem_t *sem);
int sem_unlink(FAR const char *name);
#endif

#undef EXTERN
#ifdef __cplusplus
}
#endif

#endif                          /* __INCLUDE_SEMAPHORE_H */