/*
 * include/haproxy/port_range.h
 * This file defines everything needed to manage port ranges
 *
 * Copyright (C) 2000-2020 Willy Tarreau - w@1wt.eu
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation, version 2.1
 * exclusively.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

#ifndef _HAPROXY_PORT_RANGE_H
#define _HAPROXY_PORT_RANGE_H

#include <stdlib.h>
#include <haproxy/api.h>
#include <haproxy/port_range-t.h>

#define GET_NEXT_OFF(range, off) ((off) == (range)->size - 1 ? 0 : (off) + 1)

/* return an available port from range <range>, or zero if none is left */
static inline int port_range_alloc_port(struct port_range *range)
{
	int ret;
	int get;
	int put;

	get = _HA_ATOMIC_LOAD(&range->get);
	do {
		/* barrier ot make sure get is loaded before put */
		__ha_barrier_atomic_load();
		put = _HA_ATOMIC_LOAD(&range->put_t);
		if (unlikely(put == get))
			return 0;
		ret = range->ports[get];
	} while (!(_HA_ATOMIC_CAS(&range->get, &get, GET_NEXT_OFF(range, get))));
	return ret;
}

/* release port <port> into port range <range>. Does nothing if <port> is zero
 * nor if <range> is null. The caller is responsible for marking the port
 * unused by either setting the port to zero or the range to NULL.
 */
static inline void port_range_release_port(struct port_range *range, int port)
{
	int put;

	if (!port || !range)
		return;

	put = range->put_h;
	/* put_h is reserved for producers, so that they can each get a
	 * free slot, put_t is what is used by consumers to know if there's
	 * elements available or not
	 */
	/* First reserve or slot, we know the ring buffer can't be full,
	 * as we will only ever release port we allocated before
	 */
	while (!(_HA_ATOMIC_CAS(&range->put_h, &put, GET_NEXT_OFF(range, put))));
	_HA_ATOMIC_STORE(&range->ports[put], port);
	/* Barrier to make sure the new port is visible before we change put_t */
	__ha_barrier_atomic_store();
	/* Wait until all the threads that got a slot before us are done */
	while ((volatile int)range->put_t != put)
		__ha_compiler_barrier();
	/* Let the world know we're done, and any potential consumer they
	 * can use that port.
	 */
	_HA_ATOMIC_STORE(&range->put_t, GET_NEXT_OFF(range, put));
}

/* return a new initialized port range of N ports. The ports are not
 * filled in, it's up to the caller to do it.
 */
static inline struct port_range *port_range_alloc_range(int n)
{
	struct port_range *ret;
	ret = calloc(1, sizeof(struct port_range) +
		     (n + 1) * sizeof(((struct port_range *)0)->ports[0]));
	ret->size = n + 1;
	/* Start at the first free element */
	ret->put_h = ret->put_t = n;
	return ret;
}

#endif /* _HAPROXY_PORT_RANGE_H */

/*
 * Local variables:
 *  c-indent-level: 8
 *  c-basic-offset: 8
 * End:
 */
