int main(int argc, char **argv)
{
sem_t *sem;
int val;
if (argc != 2)
err_quit("Usage: post <name>");
sem = Sem_open(argv[1], 0);
Sem_post(sem);
Sem_getvalue(sem, &val);
printf("value = %d\n", val);
exit(0);
}
int main(int argc, char **argv)
{
sem_t *sem;
int val;
if (argc != 2)
err_quit("Usage: wait <name>");
sem = Sem_open(argv[1], 0);
Sem_wait(sem);
Sem_getvalue(sem, &val);
printf("pid %ld has semaphore, value = %d\n", (long)getpid(), val);
pause();
exit(0);
}
int main(int argc, char *argv[])
{
sem_t *sem;
int val;
if(argc != 2)
err_quit("usage: semwait <name>");
sem = Sem_open(argv[1], 0);/*打开一个有名的信号量*/
Sem_wait(sem);/*测试sem是否大于0，是则减1，执行，否者阻塞*/
Sem_getvalue(sem, &val);/*获取信号的当前值*/
printf("pid %ld has semaphora value = %d\n", (long) getpid(), val);
pause();
return 0;
}