进程间通信-消息队列

互斥：矛盾 

同步：协作

消息队列

#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/msg.h>

• int msgget(key_t key,int msgflg);
• int msgctl(int msgid,int cmd,stuct msqid_ds *buf);
• cmd:
• 　　IPC_RMID
• 　　IPC_STAT
• 　　IPC_SET

• int msgend(int msqid,const void *msgp,sie_t msgsz,int msgflg);
  • msgflg:
    • IPC_NOWAT表示队列蛮不等待，返回EAGAIN
• ssize_t msgrcv(int msqid,void *msgp, size_t msgsz,long msgtyp,int msgflg);
• 基于消息队列的客户端

  • #include <unistd.h>
    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/msg.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <errno.h>
    #include <string.h>
    
    #define ERR_EXIT(m)
        do
        {
            perror(m);
            exit(EXIT_FAILURE);
        }while(0)
    
    #define MSGMAX 8192
    
    struct msgbuf
    {
        long mtype;
        char mtext[MSGMAX];
    };
    
    void echo_cli(int msgid)
    {
        int n;
        int pid;
        pid = getpid();    
        struct msgbuf msg;
        memset(&msg,0,sizeof(msg));
        *((int*)msg.mtext) = pid;
        msg.mtype = 1;
        while(fgets(msg.mtext+4,MSGMAX, stdin) != NULL)
        {
            msg.mtype = 1;
            if(msgsnd(msgid,&msg,4+strlen(msg.mtext+4), 0) < 0)
                ERR_EXIT("msgsnd");
    
            memset(msg.mtext+4, 0, MSGMAX-4);
            if((n = msgrcv(msgid, &msg, MSGMAX, pid, 0)) < 0)
                ERR_EXIT("msgrcv");
    
            fputs(msg.mtext+4,stdout);
            memset(msg.mtext+4, 0, MSGMAX-4);
        }
    }
    
    int main(int argc,char* argv[])
    {
        int msgid;
        msgid = msgget(1234,0);
        if(msgid == -1)
            ERR_EXIT("msgget failed
    ");
        printf("msgget ok,msgid=%d
    ",msgid);
        echo_cli(msgid);
    }

• 基于消息队列的服务器

  • #include <unistd.h>
    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/msg.h>
    #include <stdlib.h>
    #include <stdio.h>
    #include <errno.h>
    #include <string.h>
    
    #define ERR_EXIT(m)
        do
        {
            perror(m);
            exit(EXIT_FAILURE);
        }while(0)
    
    #define MSGMAX 8192
    struct msgbuf
    {
        long mtype;
        char mtext[MSGMAX];
    };
    
    void echo_srv(int msgid)
    {
        int n;
        struct msgbuf msg;
        memset(&msg, 0, sizeof(msg));
        while(1)
        {
            if((n = msgrcv(msgid,&msg,MSGMAX,1,0)) < 0)
                ERR_EXIT("msgsnd");
            int pid;
            pid = *((int*)msg.mtext);
            
            fputs(msg.mtext+4,stdout);
            msg.mtype = pid;
            msgsnd(msgid, &msg, n, 0);
        }
    }
    
    int main(int argc,char* argv[])
    {
        int msgid;
        msgid = msgget(1234,IPC_CREAT | 0666);
        if(msgid == -1)
            ERR_EXIT("msgget failed
    ");
        printf("msgget ok,msgid=%d
    ",msgid);
    
        echo_srv(msgid);
    }