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。

下面的玩具程序显示问题，可以在不同的处理器上重复。

任何帮助都非常感谢!

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.rn");
        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: %srnrn", 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.rn");
        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: %srnrn", 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 sendsn");
    pthread_create(&t2, NULL, MINNIEthreadFunc, "Minnie repliesn");
    pthread_create(&t3, NULL, DONALDthreadFunc, "Donald sendsn");
    pthread_create(&t4, NULL, PLUTOthreadFunc, "Pluto repliesn");
    while(1)
    {
        sleep(5);
    }
}

Answer 1

问题是您错过了错误处理。

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

此时ftok的返回值为-1。如果两个文件都缺失，ipc键值都为-1，表示所有流量共享同一个端口:)

touch /tmp/mqmickey /tmp/mqdonald

修复它。一些统计数据(用usleep(random()%10000)代替睡眠):

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

Answer 2

非常感谢sehe和VJo，

这是一个程序的修改版本，考虑了你所有的评论。

希望对别人有帮助。

伯特

/*
    We want Mickey to send a message to Minnie exclusively.
    We want Donald to send a message to pluto exclusively.  
    To compile:
    gcc mm.c -o mm -fno-stack-protector -pthread
    Requires: 
    syslog enabled and started.
    To test:
    time ./mm | { trap "" INT; sort | uniq -c | tee stats; } 
    Results:
    1503373 Donald sent a message to Pluto.
          1 Donald thread successfully started.
    1423964 Mickey sent a message to Minnie.
          1 Mickey thread successfully started.
    1423958  Minnie received: Hello, Minnie!
          1 Minnie thread successfully started.
    1503333 Pluto received: Sit, Pluto!
          1 Pluto thread successfully started.
    real    0m17.133s
    user    0m16.053s
    sys 0m5.248s
*/
#include <sys/types.h>
#include <sys/msg.h>
#include <sys/ipc.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <syslog.h>

#define MQMICKEY "/tmp/MQMickey"
#define MQDONALD "/tmp/MQDonald"
pthread_t t1,t2,t3,t4;
FILE *fMickeypointer;
FILE *fDonaldpointer;
// 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.rn"); 
    }
    /* 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: %srn", myPlutomsg.text);
    }
    /* 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.rn");
    }
    /* 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: %srn", myMinniemsg.text);
    }
    return (void *) strlen(s);
}
int main (void)
{
    /* 
        MUST create the target files first.
        The return of ftok is -1 if file is missing. If BOTH files are missing, both ipc keys 
        will be -1, meaning all traffic shares the same port. Result: one queue will acquire
        messages not intended for it!
    */
    fMickeypointer = fopen(MQMICKEY, "a");
    if(fMickeypointer == NULL) 
    {
        printf("Failed to create Mickey queue file.n");
        /* system logging */
        setlogmask (LOG_UPTO (LOG_NOTICE));
        openlog ("MickeyDonald", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);
        syslog (LOG_NOTICE, "Failed to create Mickey queue file." );
        closelog ();
        exit(91);
    }
    fDonaldpointer = fopen(MQDONALD, "a");
    if(fDonaldpointer == NULL) 
    {
        printf("Failed to create Donald queue file.rn");
        /* system logging */
        setlogmask (LOG_UPTO (LOG_NOTICE));
        openlog ("MickeyDonald", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);
        syslog (LOG_NOTICE, "Failed to create Donald queue file." );
        closelog ();
        exit(92);
    }
    ipcMickey = 0;
    ipcDonald = 0;
    /* make sure we assign DIFFERENT ipc values */  
    while(ipcMickey == ipcDonald)
    {
        ipcMickey = ftok(MQMICKEY, 63);
        if (-1==ipcMickey)
        {
            printf("ipcMickey does not exist.rn");
            /* system logging */
            setlogmask (LOG_UPTO (LOG_NOTICE));
            openlog ("MickeyDonald", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);
            syslog (LOG_NOTICE, "Failed to ftok Mickey file." );
            closelog ();
            exit(93);
        }
        ipcDonald = ftok(MQDONALD, 69);
        if (-1==ipcDonald)
        {
            printf("ipcDonald does not exist.rn");
            /* system logging */
            setlogmask (LOG_UPTO (LOG_NOTICE));
            openlog ("MickeyDonald", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);
            syslog (LOG_NOTICE, "Failed to ftok Donald file." );
            closelog ();
            exit(94);
        }
    }
    mqMickeyid = msgget(ipcMickey, IPC_CREAT | 0666);
    mqDonaldid = msgget(ipcDonald, IPC_CREAT | 0666);
    pthread_create(&t1, NULL, MICKEYthreadFunc, "Mickey sendsn");
    pthread_create(&t2, NULL, MINNIEthreadFunc, "Minnie repliesn");
    pthread_create(&t3, NULL, DONALDthreadFunc, "Donald sendsn");
    pthread_create(&t4, NULL, PLUTOthreadFunc, "Pluto repliesn");
    long exitcounter = 0;
    while(exitcounter < 100000)
    {
        exitcounter +=1;        
        usleep(100);
    }
    exit(0);
}

Answer 3

这是你的程序稍微修改过的版本:

/*
    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.rn");
        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: %srnPluto uses MQ with id = %drn", myPlutomsg.text,mqPlutoid);
        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.rn");
        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: %srnMinnie uses MQ with id = %drn", myMinniemsg.text,mqMinnieid);
        sleep(3);
    }
    return (void *) strlen(s);
}
int main (void)
{
    ipcMickey = ftok("./mqmickey", 63);
    mqMickeyid = msgget(ipcMickey, IPC_CREAT | 0666);
    printf( "mqMickeyid=%dn",mqMickeyid);
    ipcDonald = ftok("./mqdonald", 69);
    mqDonaldid = msgget(ipcDonald, IPC_CREAT | 0666);
    printf( "mqDonaldid=%dn",mqDonaldid);
    pthread_create(&t1, NULL, MICKEYthreadFunc, "Mickey sendsn");
    pthread_create(&t2, NULL, MINNIEthreadFunc, "Minnie repliesn");
    pthread_create(&t3, NULL, DONALDthreadFunc, "Donald sendsn");
    pthread_create(&t4, NULL, PLUTOthreadFunc, "Pluto repliesn");
    while(1)
    {
        sleep(5);
    }
}

我发现，由于某种原因，msgget失败了，两个mq都有相同的id，那么这是一个线程首先启动的竞争。

对于修改后的程序，执行如下操作:

touch mqmickey
touch mqdonald

先创建文件

你应该会看到消息被发送到正确的收件人。