/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (c) 1996-1999
 *      HD Associates, Inc.  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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by HD Associates, Inc
 * 4. Neither the name of the author nor the names of any co-contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY HD ASSOCIATES 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 HD ASSOCIATES 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/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <err.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sched.h>
#include <stdlib.h>
#include <sys/wait.h>

#include "prutil.h"

/* buzz: busy wait a random amount of time.
 */
static void buzz(int n)
{
        volatile int i;
        int m = random() & 0x0ffff;
        for (i = 0; i < m; i++)
                ;
}

/* Yield: Verify that "sched_yield" works for the FIFO case.
 * This runs several processes and verifies that the yield seems
 * to permit the next one on the ready queue to run.
 */
int yield(int argc, char *argv[])
{
        volatile int *p;
        int i;
        int nslaves, n;
        int master, slave;
        pid_t youngest = !0;    /* Our youngest child */
        struct sched_param set, got;
        int nloops = 1000;

        errno = 0;

        set.sched_priority = sched_get_priority_max(SCHED_FIFO);
        if (set.sched_priority == -1 && errno) {
                perror("sched_get_priority_max");
                exit(errno);
        }

        if (argc == 1)
                n = nslaves = 10;

        else if (argc != 2) {
                fprintf(stderr, "usage: prog [n_instances]\n");
                exit(-1);
        }
        else
                n = nslaves = atoi(argv[1]);

        p = (int *)mmap(0, sizeof(int),
        PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);

        if (p == (int *)-1)
                err(errno, "mmap");

        *p = 0;

        if (sched_setscheduler(0, SCHED_FIFO, &set) == -1)
                err(errno, "sched_setscheduler");

        /* I better still be SCHED_FIFO and RT_PRIO_MAX:
         */
        (void)sched_is(__LINE__, &got, SCHED_FIFO);
        if (got.sched_priority != set.sched_priority) {
                fprintf(stderr, "line %d: scheduler screwup\n",
                __LINE__);
                exit(-1);
        }

        slave = 0;
        master = 1;

        /* Fork off the slaves.
         */
        for (i = 0; i < nslaves; i++) {
                if ((youngest = fork()) == 0) {
                        /* I better still be SCHED_FIFO and RT_PRIO_MAX:
                         */
                        (void)sched_is(__LINE__, &got, SCHED_FIFO);

                        if (got.sched_priority != set.sched_priority) {
                                fprintf(stderr, "line %d: scheduler screwup\n",
                                __LINE__);
                                exit(-1);
                        }

                        master = 0;     /* I'm a slave */
                        slave = i + 1;  /* With this flag */
                        *p = slave;     /* And I live */
                        break;
                }
        }

        if (master) {
                /* If we conform the slave processes haven't run yet.
                 * The master must yield to let the first slave run.
                 */
                if (*p != 0) {
                        fprintf(stderr,
                        "Error at line %d: Writer %d has run\n", __LINE__, *p);
                        exit(-1);
                }
        }

        /* Now the master yields, the first slave runs, and yields,
         * next runs, yields, ...
         *
         * So the master should get through this first.
         */

        if (sched_yield() == -1)
                err(errno, "sched_yield");

        if (master) {
                int status;

                /* The final slave process should be the last one started.
                 */
                if (*p != nslaves) {
                        fprintf(stderr,
                        "Error at line %d: Final slave is %d not %d.\n",
                        __LINE__, *p, nslaves);
                        exit(-1);
                }

                /* Wait for our youngest to exit:
                 */
                waitpid(youngest, &status, 0);

                exit(WEXITSTATUS(status));      /* Let the slaves continue */
        }

        /* Now the first one has started up.
         */
        for (i = 0; i < nloops; i++) {
                if (((*p) % nslaves) !=
                ((slave + nslaves - 1) % nslaves)) {
                        fprintf(stderr, "%d ran before %d on iteration %d.\n",
                        *p, slave, i);
                        exit(-1);
                }
                *p = slave;

                /* Delay some random amount of time.
                 */
                buzz(slave);

                if (sched_yield() == -1)
                        err(errno, "sched_yield");
        }

        exit(0);
}
#ifdef STANDALONE_TESTS
int main(int argc, char *argv[]) { return yield(argc, argv); }
#endif