1/*-
2 * SPDX-License-Identifier: BSD-4-Clause
3 *
4 * Copyright (c) 1996-1999
5 *	HD Associates, Inc.  All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. All advertising materials mentioning features or use of this software
16 *    must display the following acknowledgement:
17 *	This product includes software developed by HD Associates, Inc
18 * 4. Neither the name of the author nor the names of any co-contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY HD ASSOCIATES AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL HD ASSOCIATES OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 */
35#include <sys/types.h>
36#include <unistd.h>
37#include <stdlib.h>
38#include <stdio.h>
39#include <errno.h>
40#include <err.h>
41#include <fcntl.h>
42#include <sys/types.h>
43#include <sys/mman.h>
44#include <sched.h>
45#include <stdlib.h>
46#include <sys/wait.h>
47
48#include "prutil.h"
49
50/* buzz: busy wait a random amount of time.
51 */
52static void buzz(int n)
53{
54	volatile int i;
55	int m = random() & 0x0ffff;
56	for (i = 0; i < m; i++)
57		;
58}
59
60/* Yield: Verify that "sched_yield" works for the FIFO case.
61 * This runs several processes and verifies that the yield seems
62 * to permit the next one on the ready queue to run.
63 */
64int yield(int argc, char *argv[])
65{
66	volatile int *p;
67	int i;
68	int nslaves, n;
69	int master, slave;
70	pid_t youngest = !0;	/* Our youngest child */
71	struct sched_param set, got;
72	int nloops = 1000;
73
74	errno = 0;
75
76	set.sched_priority = sched_get_priority_max(SCHED_FIFO);
77	if (set.sched_priority == -1 && errno) {
78		perror("sched_get_priority_max");
79		exit(errno);
80	}
81
82	if (argc == 1)
83		n = nslaves = 10;
84
85	else if (argc != 2) {
86		fprintf(stderr, "usage: prog [n_instances]\n");
87		exit(-1);
88	}
89	else
90		n = nslaves = atoi(argv[1]);
91
92	p = (int *)mmap(0, sizeof(int),
93	PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);
94
95	if (p == (int *)-1)
96		err(errno, "mmap");
97
98	*p = 0;
99
100	if (sched_setscheduler(0, SCHED_FIFO, &set) == -1)
101		err(errno, "sched_setscheduler");
102
103	/* I better still be SCHED_FIFO and RT_PRIO_MAX:
104	 */
105	(void)sched_is(__LINE__, &got, SCHED_FIFO);
106	if (got.sched_priority != set.sched_priority) {
107		fprintf(stderr, "line %d: scheduler screwup\n",
108		__LINE__);
109		exit(-1);
110	}
111
112	slave = 0;
113	master = 1;
114
115	/* Fork off the slaves.
116	 */
117	for (i = 0; i < nslaves; i++) {
118		if ((youngest = fork()) == 0) {
119			/* I better still be SCHED_FIFO and RT_PRIO_MAX:
120			 */
121			(void)sched_is(__LINE__, &got, SCHED_FIFO);
122
123			if (got.sched_priority != set.sched_priority) {
124				fprintf(stderr, "line %d: scheduler screwup\n",
125				__LINE__);
126				exit(-1);
127			}
128
129			master = 0;	/* I'm a slave */
130			slave = i + 1;	/* With this flag */
131			*p = slave;	/* And I live */
132			break;
133		}
134	}
135
136	if (master) {
137		/* If we conform the slave processes haven't run yet.
138		 * The master must yield to let the first slave run.
139		 */
140		if (*p != 0) {
141			fprintf(stderr,
142			"Error at line %d: Writer %d has run\n", __LINE__, *p);
143			exit(-1);
144		}
145	}
146
147	/* Now the master yields, the first slave runs, and yields,
148	 * next runs, yields, ...
149	 *
150	 * So the master should get through this first.
151	 */
152
153	if (sched_yield() == -1)
154		err(errno, "sched_yield");
155
156	if (master) {
157		int status;
158
159		/* The final slave process should be the last one started.
160		 */
161		if (*p != nslaves) {
162			fprintf(stderr,
163			"Error at line %d: Final slave is %d not %d.\n",
164			__LINE__, *p, nslaves);
165			exit(-1);
166		}
167
168		/* Wait for our youngest to exit:
169		 */
170		waitpid(youngest, &status, 0);
171
172		exit(WEXITSTATUS(status));	/* Let the slaves continue */
173	}
174
175	/* Now the first one has started up.
176	 */
177	for (i = 0; i < nloops; i++) {
178		if (((*p) % nslaves) !=
179		((slave + nslaves - 1) % nslaves)) {
180			fprintf(stderr, "%d ran before %d on iteration %d.\n",
181			*p, slave, i);
182			exit(-1);
183		}
184		*p = slave;
185
186		/* Delay some random amount of time.
187		 */
188		buzz(slave);
189
190		if (sched_yield() == -1)
191			err(errno, "sched_yield");
192	}
193
194	exit(0);
195}
196#ifdef STANDALONE_TESTS
197int main(int argc, char *argv[]) { return yield(argc, argv); }
198#endif
199