linux ipc之信号量

#include<unistd.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
union semun{
	int val;
	struct semid_ds *buf;
	unsigned short *array;
};
int main(){
	int sem_id = semget(IPC_PRIVATE,2,0666);
	union semun sem_args;
	unsigned short arr[2] = {1,0};
	sem_args.array = arr;
	semctl(sem_id,1,SETALL,sem_args);
	struct sembuf sem_done1[1] = {0,-1,SEM_UNDO};
	struct sembuf sem_up1[1] = {0,1,SEM_UNDO};
	struct sembuf sem_done2[1] = {1,-1,SEM_UNDO};
	struct sembuf sem_up2[1] = {1,1,SEM_UNDO};
	if(fork() == 0){
		while(1){
			semop(sem_id,sem_done1,1);
			printf("childn");
			semop(sem_id,sem_up2,1);
		}
	}else{
		while(1){
			semop(sem_id,sem_done2,1);
			printf("parentn");
			semop(sem_id,sem_up1,1);
		}
	}
	return 0;
}