producer and consumer problem,process version. using Posix mqueue.

pcprocess.c

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <semaphore.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <mqueue.h>
#define N 1
#define BUFSIZE 1024
#define LOOP 10*N
int main(int argc,char *argv)
{
    mqd_t mqd;
    pid_t producerPid,consumerPid;
    int flags=O_RDWR | O_CREAT | O_EXCL;
    unsigned int prio=0;
    //int flags=O_RDWR;
    mode_t perms=0666;
    struct mq_attr attr;
    attr.mq_maxmsg=N;
    attr.mq_msgsize=BUFSIZE;

    mqd=mq_open("/mq",flags,perms,&attr);
    if (mqd<0)
    {
        printf("error on create mqueue.\n");
        exit(0);
    }
    mq_close(mqd);
    if ((consumerPid=fork())<0)
    {
        exit(1);
    }
    else if(consumerPid==0)
    {
        //consumer
        mqd=mq_open("/mq",O_RDONLY);
        void *item=malloc(BUFSIZE);
        for (int i=0;i<LOOP;++i)
        {
            mq_receive(mqd,item,BUFSIZE,&prio);
            printf("receive %d\n",(int)*(char*)(item));
        }
        exit(0);
    }
    else
    {
        if ((producerPid=fork())<0)
        {
            exit(1);
        }
        else if (producerPid==0)
        {
            //producer
            char *item=(char*)malloc(sizeof(char));
            mqd=mq_open("/mq",O_WRONLY);
            for (int i=0;i<LOOP;++i)
            {
                *item=i%128;
                printf("send %d\n",(int)(*item));
                mq_send(mqd,item,1,0);
            }
            exit(0);
        }
        else
        {
            while(wait(NULL)!=-1)
                continue;
            mq_unlink("/mq");
            return 0;
        }
    }
}