IPC之消息队列

key_t键和ftok()函数

* 消息队列、信号量和共享内存具有内核持续性(与具体进程周期不相关)，故需要在内核用一个全局唯一的Key来标识。

- 使用例子：

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>

int main()
{
    const char *pMsgPath = "/data/home/andyawang/code/ipc/MsgQueue";
    key_t key = ftok(pMsgPath, 1);
    printf("Key : %d\n", key);
    return 0;
}

2个命令：ipcs和ipcrm
* ipcs用于显示当前内核这3种IPC的各种信息，ipcrm为删除
* 使用例子：

# ipcs
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status      
0x00000000 0          root       666        12000      6          dest         
0x00005fe7 32769      root       666        524288     2                       
0x00005fe8 65538      root       666        2097152    12  
------ Semaphore Arrays --------
key        semid      owner      perms      nsems     
0x00008708 32769      root       666        1         
0x000086f8 589826     root       666        1
------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x5ca04f5b 3473408    root		 666        0            0         

数据结构 （#include<sys/msg.h>）

struct msqid_ds
{
    struct msqid_ds {
    struct ipc_perm msg_perm;
    struct msg *msg_first;      	/* first message on queue,unused  */
    struct msg *msg_last;       	/* last message in queue,unused */
    __kernel_time_t msg_stime;  	/* last msgsnd time */
    __kernel_time_t msg_rtime;  	/* last msgrcv time */
    __kernel_time_t msg_ctime;  	/* last change time */
    unsigned long  msg_lcbytes; 	/* Reuse junk fields for 32 bit */
    unsigned long  msg_lqbytes; 	/* ditto */
    unsigned short msg_cbytes;  	/* current number of bytes on queue */
    unsigned short msg_qnum;    	/* number of messages in queue */
    unsigned short msg_qbytes;  	/* max number of bytes on queue */
    __kernel_ipc_pid_t msg_lspid;   /* pid of last msgsnd */
    __kernel_ipc_pid_t msg_lrpid;   /* last receive pid */
};

* 相关函数

- msgget()：创建或打开一个消息队列

- msgctl()：控制操作，如删除等

* 使用例子：

[MsgQueSvr,cpp]

#include <iostream>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
using namespace std;
const int MAXSIZE = 100;

// 消息的数据结构：
// * 最前必须有一个long来作为消息的类型，剩下的可自定义
struct SMsgUnit
{
    long type;
    int len;
    char data[MAXSIZE];
};

int main()
{
    struct SMsgUnit sMsg;
    key_t iKey;
    int iMsgId;

    // Get MsgQue Key
    const char *pMsgPath = "/data/home/andyawang/code/ipc/MsgQueue";
    if ((iKey = ftok(pMsgPath, 1)) == -1) {
        cout << "Ftok Err" << endl;
        return -1;
    }

    // 1.msgget
    if ((iMsgId = msgget(iKey, IPC_CREAT|IPC_EXCL|0666)) == -1) {
        cout << "Msgget Err" << endl;
        return -1;
    }

    // 2.msgrcv & msgsnd
    for(int i = 0; i < 5; i ++)
    {
        msgrcv(iMsgId, &sMsg, sizeof(struct SMsgUnit), 1, 0);
        cout << "Svr Recv Msg, type=" << sMsg.type << ", len=" << sMsg.len << ", data=" << sMsg.data << endl;
        sMsg.type = 2;
        strcpy(sMsg.data, "I Am Svr..");
        sMsg.len = strlen(sMsg.data);
        msgsnd(iMsgId, &sMsg, sizeof(struct SMsgUnit), 0);
    }

    // 3.msgctl
    if (msgctl(iMsgId, IPC_RMID, NULL) == -1) {
        cout << "Msgctl Err" << endl;
        return -1;
    }

    return 0;
}

#include <iostream>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
using namespace std;
const int MAXSIZE = 100;

struct SMsgUnit
{
    long type;
    int len;
    char data[MAXSIZE];
};

int main()
{
    struct SMsgUnit sMsg;
    key_t iKey;
    int iMsgId;

    // Get MsgQue Key
    const char *pMsgPath = "/data/home/andyawang/code/ipc/MsgQueue";
    if ((iKey = ftok(pMsgPath, 1)) == -1) {
        cout << "Ftok Err" << endl;
        return -1;
    }

    // 1.msgget
    if ((iMsgId = msgget(iKey, IPC_CREAT|0666)) == -1) {
        cout << "Msgget Err" << endl;
        return -1;
    }

    // 2.msgsnd
    sMsg.type = 1;
    strcpy(sMsg.data, "I Am Cli..");
    sMsg.len = strlen(sMsg.data);
    msgsnd(iMsgId, &sMsg, sizeof(struct SMsgUnit), 0);

    // 3.msgrcv
    msgrcv(iMsgId, &sMsg, sizeof(struct SMsgUnit), 2, 0);
    cout << "Cli Recv Msg, type=" << sMsg.type << ", len=" << sMsg.len << ", data=" << sMsg.data << endl;

    return 0;
}

IPC之消息队列

原文：http://blog.csdn.net/yyyiran/article/details/19087407