/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/time.h>
#include <sys/user.h>

#include "extern.h"

/*
 * Returns 1 if p2 is "better" than p1
 *
 * The algorithm for picking the "interesting" process is thus:
 *
 *      1) Only foreground processes are eligible - implied.
 *      2) Runnable processes are favored over anything else.  The runner
 *         with the highest cpu utilization is picked (p_estcpu).  Ties are
 *         broken by picking the highest pid.
 *      3) The sleeper with the shortest sleep time is next.  With ties,
 *         we pick out just "short-term" sleepers (TDF_SINTR == 0).
 *      4) Further ties are broken by picking the highest pid.
 *
 * If you change this, be sure to consider making the change in the kernel
 * too (^T in kern/tty.c).
 *
 * TODO - consider whether pctcpu should be used.
 */

#define ISRUN(p)        (((p)->ki_stat == SRUN) || ((p)->ki_stat == SIDL))
#define TESTAB(a, b)    ((a)<<1 | (b))
#define ONLYA   2
#define ONLYB   1
#define BOTH    3

int
proc_compare(struct kinfo_proc *p1, struct kinfo_proc *p2)
{

        if (p1 == NULL)
                return (1);
        /*
         * see if at least one of them is runnable
         */
        switch (TESTAB(ISRUN(p1), ISRUN(p2))) {
        case ONLYA:
                return (0);
        case ONLYB:
                return (1);
        case BOTH:
                /*
                 * tie - favor one with highest recent cpu utilization
                 */
                if (p2->ki_estcpu > p1->ki_estcpu)
                        return (1);
                if (p1->ki_estcpu > p2->ki_estcpu)
                        return (0);
                return (p2->ki_pid > p1->ki_pid); /* tie - return highest pid */
        }
        /*
         * weed out zombies
         */
        switch (TESTAB(p1->ki_stat == SZOMB, p2->ki_stat == SZOMB)) {
        case ONLYA:
                return (1);
        case ONLYB:
                return (0);
        case BOTH:
                return (p2->ki_pid > p1->ki_pid); /* tie - return highest pid */
        }
        /*
         * pick the one with the smallest sleep time
         */
        if (p2->ki_slptime > p1->ki_slptime)
                return (0);
        if (p1->ki_slptime > p2->ki_slptime)
                return (1);
        /*
         * favor one sleeping in a non-interruptible sleep
         */
        if (p1->ki_tdflags & TDF_SINTR && (p2->ki_tdflags & TDF_SINTR) == 0)
                return (1);
        if (p2->ki_tdflags & TDF_SINTR && (p1->ki_tdflags & TDF_SINTR) == 0)
                return (0);
        return (p2->ki_pid > p1->ki_pid);       /* tie - return highest pid */
}