msgctl | 获取和设置消息队列的属性

beyes · 发表于 2009-9-4 01:24:09

消息队列的属性保存在系统维护的数据结构 msqid_ds 中，用户可以通过函数 msgctl 获取或设置消息队列属性。msgctl 定义在头文件 sys/msg.h 中，原型如下：

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

int msgctl(int msqid, int cmd, struct msqid_ds *buf);

msgctl 系统调用对 msgqid 标识的消息队列执行 cmd 操作，系统定义了 3 种 cmd 操作： IPC_STAT , IPC_SET , IPC_RMID ，意义分别如下：

IPC_STAT

IPC_SET

IPC_RMID

测试程序：

#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <string.h>

#define BUF_SIZE    256
#define    PROJ_ID        32
#define    PATH_NAME    "."

void getmsgattr (int msgid, struct msqid_ds msq_info);

int main()
{
    /*用户自定义缓冲区*/
    struct mymsgbuf {
        long msgtype;
        char ctrlstring[BUF_SIZE];
    } msgbuffer;

    int     qid;    /*消息队列标识符*/
    int     msglen;
    key_t    msgkey;
    struct msqid_ds    msg_attr;

    /*获取键值*/
    if ((msgkey = ftok (PATH_NAME, PROJ_ID)) == -1) {
        perror ("ftok error!\n");
        exit (1);
    }

    /*获取消息队列标识符*/
    if ((qid = msgget (msgkey, IPC_CREAT|0660)) == -1) {
        perror ("ftok error!\n");
        exit (1);
    }

    getmsgattr (qid, msg_attr);    /*输出消息队列的属性*/

    /*发送一条消息到消息队列*/
    msgbuffer.msgtype = 3;
    strcpy (msgbuffer.ctrlstring, "Another message");
    msglen = sizeof (struct mymsgbuf) - 4;

    if (msgsnd (qid, &msgbuffer, msglen, 0) == -1) {
        perror ("msgsnd error!\n");
        exit (1);
    }

    getmsgattr (qid, msg_attr);    /*再输出消息队列的属性*/

    /*设置消息队列属性*/
//    msg_attr.msg_perm.uid = 1001;
//    msg_attr.msg_perm.gid = 100;

//    if (msgctl (qid, IPC_SET, &msg_attr) == -1) {
//        perror ("msg set error!\n");
//        exit (1);
//    }
    /*修改后再观察其属性*/
//    getmsgattr (qid, msg_attr);
    if (msgctl (qid, IPC_RMID, &msg_attr) == -1) {
        perror ("delete msg error!\n");
        exit (1);
    } else {
        system ("ipcs");
        exit (0);
    }

    //getmsgattr (qid, msg_attr);
    exit (0);
}

void getmsgattr (int msgid, struct msqid_ds msg_info)
{
    if (msgctl (msgid, IPC_STAT, &msg_info) == -1) {
        perror ("msgctl error!\n");
        return ;
    }
    printf ("*****information fo message queue*****\n");
    printf ("last msgsnd to msq time is %s\n", ctime (&(msg_info.msg_stime)));
    printf ("last msgrcv time from msg is %s\n", ctime (&(msg_info.msg_rtime)));
    printf ("last change msq ime is %s\n", ctime (&(msg_info.msg_rtime)));

    printf ("perm-uid is %d\n", msg_info.msg_perm.uid);
    printf ("perm-gid is %d\n", msg_info.msg_perm.gid);

    printf ("current number of bytes on queue is %d\n", msg_info.msg_cbytes);
    printf ("number of messages in queue is %d\n", msg_info.msg_qnum);
    printf ("max number of bytes on queue is %d\n", msg_info.msg_qbytes);

    printf ("pid of last msgsnd is %d\n", msg_info.msg_lspid);
    printf ("pid of last msgrcv is %d\n", msg_info.msg_lrpid);

    printf ("******information end!**********\n");
}

运行及输出：

beyes@linux-beyes:~/C/queue> ./opmsg.exe
*****information fo message queue*****
last msgsnd to msq time is Thu Jan 1 08:00:00 1970

last msgrcv time from msg is Thu Jan 1 08:00:00 1970

last change msq ime is Thu Jan 1 08:00:00 1970

perm-uid is 1000
perm-gid is 100
current number of bytes on queue is 0
number of messages in queue is 0
max number of bytes on queue is 65536
pid of last msgsnd is 0
pid of last msgrcv is 0
******information end!**********
*****information fo message queue*****
last msgsnd to msq time is Fri Sep 4 01:15:24 2009

last msgrcv time from msg is Thu Jan 1 08:00:00 1970

last change msq ime is Thu Jan 1 08:00:00 1970

perm-uid is 1000
perm-gid is 100
current number of bytes on queue is 256
number of messages in queue is 1
max number of bytes on queue is 65536
pid of last msgsnd is 13190
pid of last msgrcv is 0
msg uid is 1000
msg gid is 100
******information end!**********

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 327681     beyes     600        393216     2          dest
0x00000000 360450     beyes     600        393216     2          dest
0x00000000 393219     beyes     600        393216     2          dest
0x00000000 425988     beyes     600        393216     2          dest
0x00000000 458759     beyes     600        393216     2          dest
0x00000000 491528     beyes     600        393216     2          dest
0x00000000 524297     beyes     600        393216     2          dest
0x00000000 557066     beyes     600        393216     2          dest
0x00000000 589835     beyes     600        393216     2          dest
0x00000000 622604     beyes     600        393216     2          dest
0x00000000 655373     beyes     600        393216     2          dest
0x00000000 1605646    beyes     600        393216     2          dest
0x00000000 720911     beyes     600        393216     2          dest
0x00000000 2457616    beyes     600        5752320    2          dest
0x00000000 819217     beyes     600        393216     2          dest
0x00000000 851986     beyes     600        393216     2          dest
0x00000000 2621459    beyes     600        393216     2          dest

------ Semaphore Arrays --------
key        semid      owner      perms      nsems
0x4d08b330 196612     beyes     600        8

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages

说明：
由于程序是在普通用户权限下运行，所以无法创建消息的权限，故在程序中对设置权限(IPC_SET) 部分屏蔽掉。
在程序最后，调用了 IPC_RMID 命令，此命令删除掉消息队列中所有的消息，删除的结果是不存在这个消息队列，这从最后 ipcs 命令中也可以看出。如果在删除消息队列后，仍然调用 msgctl ，就会出现参数非法提示错误！

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[进程] msgctl | 获取和设置消息队列的属性

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