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/*
* Copyright (C) 2011 Tobias Brunner
* Hochschule fuer Technik Rapperswil
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*/
/**
* @defgroup semaphore semaphore
* @{ @ingroup threading
*/
#ifndef THREADING_SEMAPHORE_H_
#define THREADING_SEMAPHORE_H_
#include <utils/utils.h>
typedef struct semaphore_t semaphore_t;
/**
* A semaphore is basically an integer whose value is never allowed to be
* lower than 0. Two operations can be performed on it: increment the
* value by one, and decrement the value by one. If the value is currently
* zero, then the decrement operation will blcok until the value becomes
* greater than zero.
*/
struct semaphore_t {
/**
* Decrease the value by one, if it is greater than zero. Otherwise the
* current thread is blocked and it waits until the value increases.
*/
void (*wait)(semaphore_t *this);
/**
* Decrease the value by one, if it is greater than zero. Otherwise the
* current thread is blocked and it waits until the value increases, or the
* call times out.
*
* @param timeout timeout im ms
* @return TRUE if timed out, FALSE otherwise
*/
bool (*timed_wait)(semaphore_t *this, u_int timeout);
/**
* Decrease the value by one, if it is greater than zero. Otherwise the
* current thread is blocked and it waits until the value increases, or the
* call times out.
*
* The passed timeval should be calculated based on the time_monotonic()
* function.
*
* @param tv absolute time until timeout
* @return TRUE if timed out, FALSE otherwise
*/
bool (*timed_wait_abs)(semaphore_t *this, timeval_t tv);
/**
* Increase the value by one. If the value becomes greater than zero, then
* another thread waiting will be woken up.
*/
void (*post)(semaphore_t *this);
/**
* Destroy a semaphore and free its resources.
*/
void (*destroy)(semaphore_t *this);
};
/**
* Create a semaphore instance.
*
* @param value initial value (typically 0)
* @return semaphore instance
*/
semaphore_t *semaphore_create(u_int value);
#endif /** THREADING_SEMAPHORE_H_ @} */
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