/* finally, the main() function. */
void main()
{
int sem_set_id; /* ID of the semaphore set. */
union semun sem_val; /* semaphore value, for semctl(). */
int child_pid; /* PID of our child process. */
int i; /* counter for loop operation. */
int rc; /* return value of system calls. */
/* create a semaphore set with ID 250, with one semaphore */
/* in it, with access only to the owner. */
sem_set_id = semget(SEM_ID, 1, IPC_CREAT | 0600);
if (sem_set_id == -1) {
perror("main: semget");
exit(1);
}
/* intialize the first (and single) semaphore in our set to '1'. */
sem_val.val = 1;
rc = semctl(sem_set_id, 0, SETVAL, sem_val);
if (rc == -1) {
perror("main: semctl");
exit(1);
}
/* create a set of child processes that will compete on the semaphore */
for (i=0; i<NUM_PROCS; i++) {
child_pid = fork();
switch(child_pid) {
case -1:
perror("fork");
exit(1);
case 0: /* we're at child process. */
do_child_loop(sem_set_id, FILE_NAME);
exit(0);
default: /* we're at parent process. */
break;
}
}
/* wait for all children to finish running */
for (i=0; i<NUM_PROCS; i++) {
int child_status;
wait(&child_status);
}
printf("main: we're done\n");
fflush(stdout);
}
int main(int argc, char **argv)
{
int sem_set_id; //信号灯集的ID
union semun sem_val; //信号灯的数值, 用于 semctl()
int child_pid; //子进程的进程号
int i;
int rc;
//建立信号灯集, ID是250, 其中只有一个信号灯
sem_set_id = semget(SEM_ID, 1, IPC_CREAT | 0600);
if (sem_set_id == -1) {
perror("main: semget");
exit(1);
}
//把第一个信号灯的数值设置为1
sem_val.val = 1;
rc = semctl(sem_set_id, 0, SETVAL, sem_val);
if (rc == -1) {
perror("main: semctl");
exit(1);
}
//建立一些子进程, 使它们可以同时以竞争的方式访问信号灯
for (i=0; i<NUM_PROCS; i++) {
child_pid = fork();
switch(child_pid) {
case -1:
perror("fork");
exit(1);
case 0: //子进程
do_child_loop(sem_set_id, FILE_NAME);
exit(0);
default: //父进程接着运行
break;
}
}
//等待子进程结束
for (i=0; i<NUM_PROCS; i++) {
int child_status;
wait(&child_status);
}
printf("main: we're done\n");
fflush(stdout);
return 0;
}
