Linux 进程信号量

#include<stdlib.h>
#include<stdio.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<pthread.h>
#include<sys/shm.h>
#include<memory.h>

union semun {
               int              val;    /* Value for SETVAL */
               struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */
               unsigned short  *array;  /* Array for GETALL, SETALL */
               struct seminfo  *__buf;  /* Buffer for IPC_INFO
                                           (Linux-specific) */
           };

int main(){
    int shmid=shmget(,sizeof(int),IPC_CREAT|);
    int* p=(int*)shmat(shmid,,);
    memset(p,,sizeof(int));
    union semun sem;
    sem.val=;
    struct sembuf pv[]={{,-,},{,,}};

    int semid=semget(,,IPC_CREAT|);
    semctl(semid,,SETVAL,sem);
    pid_t pid=fork();
    if(pid==){
        semop(semid,pv,);
        printf("sub read p %d\n",*p);
        sleep();
        semop(semid,&pv[],);
    }else if(pid>){
        semop(semid,pv,);
        *p=;
        printf("main\n");
        sleep();
        semop(semid,&pv[],);
        wait();
    }

}