include/haproxy/ticks.h

/*
 * include/haproxy/ticks.h
 * Functions and macros for manipulation of expiration timers
 *
 * 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
 */

/*
 * Using a mix of milliseconds and timeval for internal timers is expensive and
 * overkill, because we don't need such a precision to compute timeouts.
 * So we're converting them to "ticks".
 *
 * A tick is a representation of a date relative to another one, and is
 * measured in milliseconds. The natural usage is to represent an absolute date
 * relative to the current date. Since it is not practical to update all values
 * each time the current date changes, instead we use the absolute date rounded
 * down to fit in a tick. We then have to compare a tick to the current date to
 * know whether it is in the future or in the past. If a tick is below the
 * current date, it is in the past. If it is above, it is in the future. The
 * values will wrap so we can't compare that easily, instead we check the sign
 * of the difference between a tick and the current date.
 *
 * Proceeding like this allows us to manipulate dates that are stored in
 * scalars with enough precision and range. For this reason, we store ticks in
 * 32-bit integers. This is enough to handle dates that are between 24.85 days
 * in the past and as much in the future.
 * 
 * We must both support absolute dates (well in fact, dates relative to now+/-
 * 24 days), and intervals (for timeouts). Both types need an "eternity" magic
 * value. For optimal code generation, we'll use zero as the magic value
 * indicating that an expiration timer or a timeout is not set. We have to
 * check that we don't return this value when adding timeouts to <now>. If a
 * computation returns 0, we must increase it to 1 (which will push the timeout
 * 1 ms further). For this reason, timeouts must not be added by hand but via
 * the dedicated tick_add() function.
 */

#ifndef _HAPROXY_TICKS_H
#define _HAPROXY_TICKS_H

#include <haproxy/api.h>

#define TICK_ETERNITY   0

/* right now, ticks are milliseconds. Both negative ms and negative ticks
 * indicate eternity.
 */
#define MS_TO_TICKS(ms) (ms)
#define TICKS_TO_MS(tk) (tk)

/* return 1 if tick is set, otherwise 0 */
static inline int tick_isset(int expire)
{
	return expire != 0;
}

/* Add <timeout> to <now>, and return the resulting expiration date.
 * <timeout> will not be checked for null values.
 */
static inline int tick_add(int now, int timeout)
{
	now += timeout;
	if (unlikely(!now))
		now++;    /* unfortunate value */
	return now;
}

/* add <timeout> to <now> if it is set, otherwise set it to eternity.
 * Return the resulting expiration date.
 */
static inline int tick_add_ifset(int now, int timeout)
{
	if (!timeout)
		return TICK_ETERNITY;
	return tick_add(now, timeout);
}

/* return 1 if timer <t1> is before <t2>, none of which can be infinite. */
static inline int tick_is_lt(int t1, int t2)
{
	return (t1 - t2) < 0;
}

/* return 1 if timer <t1> is before or equal to <t2>, none of which can be infinite. */
static inline int tick_is_le(int t1, int t2)
{
	return (t1 - t2) <= 0;
}

/* return 1 if timer <timer> is expired at date <now>, otherwise zero */
static inline int tick_is_expired(int timer, int now)
{
	if (unlikely(!tick_isset(timer)))
		return 0;
	if (unlikely((timer - now) <= 0))
		return 1;
	return 0;
}

/* return the first one of the two timers, both of which may be infinite */
static inline int tick_first(int t1, int t2)
{
	if (!tick_isset(t1))
		return t2;
	if (!tick_isset(t2))
		return t1;
	if ((t1 - t2) <= 0)
		return t1;
	else
		return t2;
}

/* return the first one of the two timers, where only the first one may be infinite */
static inline int tick_first_2nz(int t1, int t2)
{
	if (!tick_isset(t1))
		return t2;
	if ((t1 - t2) <= 0)
		return t1;
	else
		return t2;
}

/* return the number of ticks remaining from <now> to <exp>, or zero if expired */
static inline int tick_remain(int now, int exp)
{
	if (tick_is_expired(exp, now))
		return 0;
	return exp - now;
}

#endif /* _HAPROXY_TICKS_H */

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