【Linux】巧妙运用＜ 信号量 ＞控制 ＜两个线程＞之间＜谁先执行＞

#include <semaphore.h>
#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
<p>sem_t s1, s2;</p><p>void<em> runner(void</em> p) {
long tnum = (long)p;
for (int i = 1; i <= 5; i++) {
if (tnum == 0) {
sem_wait(&s1);
printf("Thread %ld: %d\n", tnum, i);
sem_post(&s2);
} else {
sem_wait(&s2);
printf("Thread %ld: %d\n", tnum, i);
sem_post(&s1);
}
}
return NULL;
}</p><p>int main(int argc, char* argv[]) {
pthread_t tid1, tid2;
long t1 = 0, t2 = 1;</p><pre class="brush:php;toolbar:false;"><code>if (argc != 2) {
    fprintf(stderr, "Usage: %s <0|1>\n", argv[0]);
    exit(1);
}

int first = atoi(argv[1]);
if (first == 0) {
    sem_init(&s1, 0, 1);
    sem_init(&s2, 0, 0);
} else if (first == 1) {
    sem_init(&s1, 0, 0);
    sem_init(&s2, 0, 1);
} else {
    fprintf(stderr, "Invalid argument. Use 0 or 1.\n");
    exit(1);
}

pthread_create(&tid1, NULL, runner, (void*)t1);
pthread_create(&tid2, NULL, runner, (void*)t2);

pthread_join(tid1, NULL);
pthread_join(tid2, NULL);

sem_destroy(&s1);
sem_destroy(&s2);

return 0;