/*
 * Active Router Transport Protocol (ARTP) implementation
 * Copyright (c) 2004, Tomas Rebok
 * All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the "BSD License" which is
 * distributed with the software in the file LICENSE.
 *
 * 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 BSD
 * License for more details.
 */

/** @file
 * Help macros for readers/writers problem.
 * @author Tomas Rebok
 * @date 2004
 */


#ifndef ARTP_RWLOCKS_H
#define ARTP_RWLOCKS_H   1


/** Initialize all necessary structures.
 * This macro initializes all necessary mutexes and counters.
 */
#define RW_INIT(x, y, z, wsem, rsem, wcount, rcount) {\
	if ((pthread_mutex_init(&x, NULL) != 0)\
            || (pthread_mutex_init(&y, NULL) != 0)\
            || (pthread_mutex_init(&z, NULL) != 0)\
            || (pthread_mutex_init(&wsem, NULL) != 0)\
            || (pthread_mutex_init(&rsem, NULL) != 0))\
        return E_MEMORY_FAIL;\
	wcount = 0;\
	rcount = 0;\
}


/** Readers lock.
 * This macro is used for readers. There can be more than one reader 
 * simultaneously, but first writer stops new readers till the end of the
 * writer(s) code.
 */
#define READERS_LOCK(x, y, z, wsem, rsem, wcount, rcount) {\
	pthread_mutex_lock(&z);\
		pthread_mutex_lock(&rsem);\
			pthread_mutex_lock(&x);\
				(rcount)++;\
				if ((rcount) == 1)\
					pthread_mutex_lock(&wsem);\
			pthread_mutex_unlock(&x);\
		pthread_mutex_unlock(&rsem);\
	pthread_mutex_unlock(&z);\
}


/** Readers unlock.
 * This macro unlocks previously locked readers lock. It decreases the count
 * of readers, too.
 */
#define READERS_UNLOCK(x, y, z, wsem, rsem, wcount, rcount) {\
	pthread_mutex_lock(&x);\
		(rcount)--;\
		if ((rcount) == 0)\
			pthread_mutex_unlock(&wsem);\
	pthread_mutex_unlock(&x);\
}


/** Writers lock.
 * This macro is used for writers to lock. There can be only one writer at the
 * moment, no readers are accepted, too. Waiting writer stops all new readers
 * till its end.
 */
#define WRITERS_LOCK(x, y, z, wsem, rsem, wcount, rcount) {\
	pthread_mutex_lock(&y);\
		(wcount)++;\
		if ((wcount) == 1)\
			pthread_mutex_lock(&rsem);\
	pthread_mutex_unlock(&y);\
	pthread_mutex_lock(&wsem);\
}


/** Writers unlock.
 * This macro unlocks previously locked writers lock. It decreases the count
 * of writers, too.
 */
#define WRITERS_UNLOCK(x, y, z, wsem, rsem, wcount, rcount) {\
	pthread_mutex_unlock(&wsem);\
	pthread_mutex_lock(&y);\
		(wcount)--;\
		if ((wcount) == 0)\
			pthread_mutex_unlock(&rsem);\
	pthread_mutex_unlock(&y);\
}


#endif

/* vim: set ts=4 : */