2 * SPDX-License-Identifier: BSD-4-Clause
4 * Copyright (c) 1996-1999
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36 #include <sys/types.h>
43 #include <sys/types.h>
51 /* buzz: busy wait a random amount of time.
53 static void buzz(int n)
56 int m = random() & 0x0ffff;
57 for (i = 0; i < m; i++)
61 /* Yield: Verify that "sched_yield" works for the FIFO case.
62 * This runs several processes and verifies that the yield seems
63 * to permit the next one on the ready queue to run.
65 int yield(int argc, char *argv[])
71 pid_t youngest = !0; /* Our youngest child */
72 struct sched_param set, got;
77 set.sched_priority = sched_get_priority_max(SCHED_FIFO);
78 if (set.sched_priority == -1 && errno) {
79 perror("sched_get_priority_max");
87 fprintf(stderr, "usage: prog [n_instances]\n");
91 n = nslaves = atoi(argv[1]);
93 p = (int *)mmap(0, sizeof(int),
94 PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED, -1, 0);
101 if (sched_setscheduler(0, SCHED_FIFO, &set) == -1)
102 err(errno, "sched_setscheduler");
104 /* I better still be SCHED_FIFO and RT_PRIO_MAX:
106 (void)sched_is(__LINE__, &got, SCHED_FIFO);
107 if (got.sched_priority != set.sched_priority) {
108 fprintf(stderr, "line %d: scheduler screwup\n",
116 /* Fork off the slaves.
118 for (i = 0; i < nslaves; i++) {
119 if ((youngest = fork()) == 0) {
120 /* I better still be SCHED_FIFO and RT_PRIO_MAX:
122 (void)sched_is(__LINE__, &got, SCHED_FIFO);
124 if (got.sched_priority != set.sched_priority) {
125 fprintf(stderr, "line %d: scheduler screwup\n",
130 master = 0; /* I'm a slave */
131 slave = i + 1; /* With this flag */
132 *p = slave; /* And I live */
138 /* If we conform the slave processes haven't run yet.
139 * The master must yield to let the first slave run.
143 "Error at line %d: Writer %d has run\n", __LINE__, *p);
148 /* Now the master yields, the first slave runs, and yields,
149 * next runs, yields, ...
151 * So the master should get through this first.
154 if (sched_yield() == -1)
155 err(errno, "sched_yield");
160 /* The final slave process should be the last one started.
164 "Error at line %d: Final slave is %d not %d.\n",
165 __LINE__, *p, nslaves);
169 /* Wait for our youngest to exit:
171 waitpid(youngest, &status, 0);
173 exit(WEXITSTATUS(status)); /* Let the slaves continue */
176 /* Now the first one has started up.
178 for (i = 0; i < nloops; i++) {
179 if (((*p) % nslaves) !=
180 ((slave + nslaves - 1) % nslaves)) {
181 fprintf(stderr, "%d ran before %d on iteration %d.\n",
187 /* Delay some random amount of time.
191 if (sched_yield() == -1)
192 err(errno, "sched_yield");
197 #ifdef STANDALONE_TESTS
198 int main(int argc, char *argv[]) { return yield(argc, argv); }