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/*
* Copyright (C) 2015 Martine Lenders <mlenders@inf.fu-berlin.de>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @defgroup sys_sema Semaphores
* @ingroup sys
* @brief Lightweight semaphore implementation
* @{
*
* @file
* @brief Semaphore definitions
*
* @author Martine Lenders <mlenders@inf.fu-berlin.de>
* @author Christian Mehlis <mehlis@inf.fu-berlin.de>
* @author René Kijewski <kijewski@inf.fu-berlin.de>
*/
#ifndef SEM_H_
#define SEM_H_
#include "msg.h"
#include "priority_queue.h"
#include "timex.h"
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief Creates semaphore statically.
*
* @param[in] value Initial value for the semaphore.
*
* @return Statically initialized semaphore.
*/
#define SEMA_CREATE(value) { (value), PRIORITY_QUEUE_INIT }
/**
* @brief A Semaphore.
*/
typedef struct {
volatile unsigned int value; /**< value of the semaphore */
priority_queue_t queue; /**< list of threads waiting for the semaphore */
} sema_t;
/**
* @brief Creates semaphore dynamically.
*
* @see <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_init.html">
* The Open Group Base Specifications Issue 7, sem_init()
* </a> (without `pshared` parameter)
*
* @param[out] sema The created semaphore.
* @param[in] value Initial value for the semaphore.
*
* @return 0 on success.
* @return -EINVAL, if semaphore is invalid.
*/
int sema_create(sema_t *sema, unsigned int value);
/**
* @brief Destroys a semaphore.
*
* @see <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_destroy.html">
* The Open Group Base Specifications Issue 7, sem_destroy()
* </a>
*
* @param[in] sema The semaphore to destroy.
*
* @return 0 on success.
* @return -EINVAL, if semaphore is invalid.
*/
int sema_destroy(sema_t *sema);
/**
* @brief Wait for a semaphore being posted.
*
* @pre Message queue of active thread is initialized (see @ref msg_init_queue()).
*
* @param[in] sema A semaphore.
* @param[in] timeout Time in microseconds until the semaphore times out. 0 for no timeout.
* @param[out] msg Container for a spurious message during the timed wait (result == -EAGAIN).
*
* @return 0 on success
* @return -EINVAL, if semaphore is invalid.
* @return -ETIMEDOUT, if the semaphore times out.
* @return -ECANCELED, if the semaphore was destroyed.
* @return -EAGAIN, if the thread received a message while waiting for the lock.
*/
int sema_wait_timed_msg(sema_t *sema, uint64_t timeout, msg_t *msg);
/**
* @brief Wait for a semaphore being posted (without timeout).
*
* @param[in] sema A semaphore.
* @param[out] msg Container for a spurious message during the timed wait (result == -EAGAIN).
*
* @return 0 on success
* @return -EINVAL, if semaphore is invalid.
* @return -ECANCELED, if the semaphore was destroyed.
* @return -EAGAIN, if the thread received a message while waiting for the lock.
*/
static inline int sema_wait_msg(sema_t *sema, msg_t *msg)
{
return sema_wait_timed_msg(sema, 0, msg);
}
/**
* @brief Wait for a semaphore being posted (dropping spurious messages).
* @details Any spurious messages received while waiting for the semaphore are silently dropped.
*
* @param[in] sema A semaphore.
* @param[in] timeout Time in microseconds until the semaphore times out. 0 for no timeout.
*
* @return 0 on success
* @return -EINVAL, if semaphore is invalid.
* @return -ETIMEDOUT, if the semaphore times out.
* @return -ECANCELED, if the semaphore was destroyed.
*/
int sema_wait_timed(sema_t *sema, uint64_t timeout);
/**
* @brief Wait for a semaphore being posted (without timeout, dropping spurious messages).
*
* @param[in] sema A semaphore.
*
* @return 0 on success
* @return -EINVAL, if semaphore is invalid.
* @return -ECANCELED, if the semaphore was destroyed.
*/
static inline int sema_wait(sema_t *sema)
{
return sema_wait_timed(sema, 0);
}
/**
* @brief Signal semaphore.
*
* @param[in] sema A semaphore.
*
* @return 0, on success
* @return -EINVAL, if semaphore is invalid.
* @return -EOVERFLOW, if the semaphore's value would overflow.
*/
int sema_post(sema_t *sema);
#ifdef __cplusplus
}
#endif
#endif /* SEM_H_ */
/** @} */
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