线程从队列中获取其他线程的IPC消息(Linux)

Question

当我在Linux上有两个不同的IPC消息队列时,有时会抓取来自错误队列的消息.

以下玩具程序显示问题,可以在不同的处理器上重复.

任何帮助非常感谢!

伯特

/*
    To compile;
    gcc MM.c -o mm -fno-stack-protector -pthread

    We want Mickey to send a message to Minnie exclusively.
    We want Donald to send a message to pluto exclusively.

    Problem: Pluto intercepts Minnie's messages.

    Listing gives:

    $ ./mm
    Mickey thread successfully started.
    Minnie thread successfully started.
    Pluto thread successfully started.
    Donald thread successfully started.
    Donald sent a message to Pluto.
    Mickey sent a message to Minnie.
    Pluto received: Sit, Pluto!

    Minnie received: Hello, Minnie!

    Mickey sent a message to Minnie.  (100 times)

    Pluto received: Hello, Minnie!
*/
#include <sys/types.h>
#include <sys/msg.h>
#include <sys/ipc.h>
#include <string.h>
#include <stdio.h>

pthread_t t1,t2,t3,t4;  

// Mickey send
key_t ipcMickey;
int mqMickeyid;
char helloMickeymsg[] = {"Hello, Minnie!"};
struct { long type; char text[100]; } myMickeymsg;

// Minnie get
int mqMinnieid;
struct { long type; char text[100]; } myMinniemsg;

// Donald send
key_t ipcDonald;
int mqDonaldid;
char helloDonaldmsg[] = {"Sit, Pluto!"};
struct { long type; char text[100]; } myDonaldmsg;

// Pluto get
int mqPlutoid;
struct { long type; char text[100]; } myPlutomsg;

static void * DONALDthreadFunc(void *arg)
{
    printf("Donald thread successfully started.\n");
    char *s = (char *) arg;

    while(1)
    {
        //send
        memset(myDonaldmsg.text, 0, 100); 
        strncpy(myDonaldmsg.text, helloDonaldmsg, strlen(helloDonaldmsg));
        myDonaldmsg.type = 1;
        msgsnd(mqDonaldid, &myDonaldmsg, sizeof(myDonaldmsg), 0);
        printf("Donald sent a message to Pluto.\r\n");
        sleep(4);
    }

    /* just a formality */
    return (void *) strlen(s);
}

static void * PLUTOthreadFunc(void *arg)
{
    printf("Pluto thread successfully started.\n");
    char *s = (char *) arg;

    while(1)
    {
        //receive
        mqPlutoid = msgget(ipcDonald, 0);
        msgrcv(mqPlutoid, &myPlutomsg, sizeof(myPlutomsg), 0, 0);
        printf("Pluto received: %s\r\n\r\n", myPlutomsg.text);
        sleep(1);
    }

    /* just a formality */
    return (void *) strlen(s);
}

static void * MICKEYthreadFunc(void *arg)
{
    printf("Mickey thread successfully started.\n");
    char *s = (char *) arg;

    while(1)
    {
        //send
        memset(myMickeymsg.text, 0, 100); 
        strncpy(myMickeymsg.text, helloMickeymsg, strlen(helloMickeymsg));
        myMickeymsg.type = 1;
        msgsnd(mqMickeyid, &myMickeymsg, sizeof(myMickeymsg), 0);
        printf("Mickey sent a message to Minnie.\r\n");
        usleep(10000);
    }

    /* just a formality */
    return (void *) strlen(s);
}

static void * MINNIEthreadFunc(void *arg)
{
    printf("Minnie thread successfully started.\n");
    char *s = (char *) arg;

    while(1)
    {
        //receive
        mqMinnieid = msgget(ipcMickey, 0);
        msgrcv(mqMinnieid, &myMinniemsg, sizeof(myMinniemsg), 0, 0);
        printf("Minnie received: %s\r\n\r\n", myMinniemsg.text);
        sleep(3);
    }

    return (void *) strlen(s);
}

int main (void) 
{
        ipcMickey = ftok("/tmp/mqmickey", 63);
        mqMickeyid = msgget(ipcMickey, IPC_CREAT | 0666);

    ipcDonald = ftok("/tmp/mqdonald", 69);
        mqDonaldid = msgget(ipcDonald, IPC_CREAT | 0666);

    pthread_create(&t1, NULL, MICKEYthreadFunc, "Mickey sends\n");
    pthread_create(&t2, NULL, MINNIEthreadFunc, "Minnie replies\n");
    pthread_create(&t3, NULL, DONALDthreadFunc, "Donald sends\n");
    pthread_create(&t4, NULL, PLUTOthreadFunc, "Pluto replies\n");

    while(1)
    {
        sleep(5);
    }
}

Answer 1

问题是你错过了错误处理.

包括

ipcMickey = ftok("/tmp/mqmickey", 63);
if (-1==ipcMickey)
{
    perror("ipcMickey");
    exit(255);
}
ipcDonald = ftok("/tmp/mqdonald", 69);
if (-1==ipcDonald)
{
    perror("ipcDonald");
    exit(255);
}

你很快就会发现

./mm
ipcDonald: No such file or directory

ftok在这种情况下,返回值为-1.如果两个文件都丢失,则两个ipc键都为-1,表示所有流量共享同一个端口:)

所以

touch /tmp/mqmickey /tmp/mqdonald

解决它.一些统计数据(用睡眠代替usleep(random()%10000)):

gcc MM.c -o mm -O3 -fno-stack-protector -pthread
time ./mm | { trap "" INT; sort | uniq -c | tee stats; } 
  16047 
      1 Donald sent a 
   8054 Donald sent a message to Pluto.
      1 Donald thread successfully started.
   8040 Mickey sent a message to Minnie.
      1 Mickey thread successfully started.
   8065 Minnie received: Hello, Minnie!
      1 Minnie thread successfully started.
   7982 Pluto received: Sit, Pluto!
      1 Pluto thread successfully started.


real    0m40.814s
user    0m0.168s
sys 0m0.092s