IPC System V - 消息队列创建

Posted 2023-02-16

【中文标题】IPC System V - 消息队列创建

【英文标题】：IPC System V - Message Queue creation

【发布时间】：2014-10-23 10:45:59

【问题描述】：

我错过了在 IPC System V 中创建多个消息队列的理解问题。

我的问题是：主进程创建 NB_fils 子进程。每个进程（包括主进程）都拥有一个消息队列。子进程 i (0

这是我的作品：

#define SVID_SOURCE 1
#define NB_FILS 4
#define MSG_SIZE 128 

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#include <unistd.h>
#include <sys/wait.h>
#include <sys/ipc.h>
#include <sys/msg.h>

/* Message structure */
typedef struct msgbuf
    long mtype; 
    int msg_val; 
    int mq_index; 
     message_buf; 

int main(int argc, char **argv)
    int mq[NB_FILS + 1]; /* There are totally NB_FILS + 1 message queues */
    int i = 0;
    int j = 0; 
    int proc_index = -1; 
    char path[14] = "File_msg";
    key_t cle; 
    int max_msg_i = 0; 
    message_buf msg_send; 
    message_buf msg_rcv; 

    /* Creation of NB_FILS + 1 message queues */
    for(i = 0; i < NB_FILS + 1; i++)
        /* cle = ftok(".", i); */ <=======================================
         cle = ftok(path, i);     <=======================================
        mq[i] = msgget(cle, 0666|IPC_CREAT);
        

    /* Creation of NB_FILS child process */
    for(i = 0; i < NB_FILS; i++)
        if(fork() > 0)
            break; 
         

    /* The child process */
    if(i != NB_FILS)
        int somme = 0; 
        proc_index = i; 
        printf("(Pid=%d) My index is %d\n", getpid(), proc_index);

        /* Message creation */      
        srand(getpid()); 
        max_msg_i =  (int) (NB_FILS*(float)rand()/RAND_MAX);
        msg_send.msg_val = max_msg_i; 
        msg_send.mtype = 1L; 
        msg_send.mq_index = proc_index; 
        printf("(Pid=%d) I'm waiting for %d messages from the main process\n", getpid(), msg_send.msg_val);

        /* Send message to message queue associated with the main process */
        msgsnd(mq[NB_FILS], &msg_send, 2*sizeof(int) + sizeof(long), 1L); 

        /* At the owned message queue, child process waits for max_msg_i message sent from the main process */
        for(j = 0; j < max_msg_i; j++)
            msgrcv(mq[proc_index], &msg_rcv, 2*sizeof(int) + sizeof(long), 1L, 0);
            printf("(Pid=%d) I have received the message containing value %d of from the main process \n", getpid(), msg_rcv.msg_val); 
            somme += msg_rcv.msg_val; 
            

        printf("(Pid=%d) Sum of %d values received: %d\n", getpid(), max_msg_i, somme);

        /* Drop the queue message */ 
        msgctl(mq[proc_index], IPC_RMID, 0);
        

    /* The main process */
    else
        srand(time(NULL)); 
        /* At the owned message queue, the main process wait for values max_msg_i (1 <= max_msg_i <= NB_FILS) sent by 
         * the child process and send back to them max_msg_i messages. */
        for(i = 0; i < NB_FILS; i++)
            msgrcv(mq[NB_FILS], &msg_rcv,2*sizeof(int) + sizeof(long), 1L, 0); 
            printf("(P)J'ai reçu le message: msg_val = %d, mq_index = %d\n", msg_rcv.msg_val, msg_rcv.mq_index); 

            /* Creat max_msg_i messages and send to process i */    
            for(j = 0; j < msg_rcv.msg_val; j++)
                msg_send.msg_val =  (int) (100*(float)rand()/RAND_MAX);
                msg_send.mtype = 1L; 
                msg_send.mq_index = msg_rcv.mq_index; 
                msgsnd(mq[msg_rcv.mq_index], &msg_send, 2*sizeof(int) + sizeof(long), 1L); 
                
            

        /* Drop the queue message */
        msgctl(mq[NB_FILS], IPC_RMID, 0);  
        

    return EXIT_SUCCESS; 
    

我的问题集中在两行：

 cle = ftok(".", i);  <=======================================
  /* cle = ftok(path, i); */     <=======================================

当我尝试使用 cle = ftok(".", i) 时，它运行良好。但对于另一个，它总是显示 喜欢：

(Pid=3813) My index is 0
(Pid=3813) I'm waiting for 1 messages from the main process
(Pid=3813) I have received the message containing value 1 of from the main process 
(Pid=3813) Sum of 1 values received: 1
(Pid=3814) My index is 1
(Pid=3814) I'm waiting for 3 messages from the main process
(Pid=3814) I have received the message containing value 3 of from the main process 
(Pid=3815) My index is 2
(Pid=3815) I'm waiting for 2 messages from the main process
(Pid=3814) I have received the message containing value 2 of from the main process 
(Pid=3816) My index is 3
(Pid=3816) I'm waiting for 0 messages from the main process
(Pid=3814) I have received the message containing value 0 of from the main process 
(Pid=3814) Sum of 3 values received: 5
(Pid=3815) I have received the message containing value -1080789062 of from the main process 
(Pid=3815) I have received the message containing value -1080789062 of from the main process 
(Pid=3815) Sum of 2 values received: 2133389172
(P)I have received: msg_val = -1080789062, mq_index = 47
(P)I have received: msg_val = -1080789062, mq_index = 47
(P)I have received: msg_val = -1080789062, mq_index = 47
(P)I have received: msg_val = -1080789062, mq_index = 47
(Pid=3816) Sum of 0 values received: 0

就像消息没有准确发送一样。

谁能告诉我是什么问题。

非常感谢。

【问题讨论】：

你可以开始检查ftok的返回值是否失败。也尝试给出File_msg 的完整路径。

【参考方案1】：

调用 ftok() 时需要为第一个参数指定一个现有文件。 作为 ”。”直接指向本地（存在），这在您的示例中有效。 但我怀疑当前目录中是否存在名为“File_msg”的文件，因此您会收到错误消息。 请改用现有文件的相对或绝对路径。