c - 读取 posix 消息队列时文件描述符错误

Question

存在类似的线程，但没有一个有帮助。我在 Linux 下使用以下代码读取时遇到错误的文件描述符错误。当使用 O_CREAT 标志进行认证时，我还指定了队列属性。任何想法？谢谢。

#include <stdio.h>
#include <mqueue.h>
#include <pthread.h>
#include <errno.h>
#include <string.h>


#define Log(...) printf(__VA_ARGS__); fflush(stdout)
int error;

void* producer(void* arg)   {
    Log("producer\n");

    mqd_t q = mq_open("/ytm", O_RDWR);
    mq_send(q, "kardeshians", sizeof("kardeshians"), 1);

}


void* consumer(void* arg)    {

    Log("consumer\n");
    char buff[32];
    mqd_t q = mq_open("/ytm", O_RDONLY);
    int prio;

    while(1)    {
        error =  mq_receive(q,buff,sizeof(buff), NULL);
        if(error)   {
            printf("read error %d  %s\n", errno, strerror(errno));
        }
    }

}



int main()  {

    struct mq_attr attr;
    attr.mq_maxmsg = 10;
    attr.mq_msgsize = 32;
    mqd_t queue = mq_open("/ytm", O_CREAT | O_RDWR, 0, &attr);


    pthread_t tid;
    pthread_create(&tid, 0 , producer, 0);
    pthread_create(&tid, 0 , consumer, 0);


    while(1);
}

Answer 1

问题出在执行权限和消息大小上。以 root 身份运行并使读取缓冲区大小大于 mq_msgsize 后，它就可以工作了。感谢您的错误检查建议。这是工作代码:

#include <stdio.h>

#include <mqueue.h>
#include <pthread.h>

#include <errno.h>
#include <string.h>


#define Log(...) printf(__VA_ARGS__); fflush(stdout)
int error;

void* producer(void* arg)   {
    Log("producer\n");

    mqd_t q = mq_open("/ytm", O_RDWR);

    if(q == -1)  {
        printf("mq_open error %d  %s\n", errno, strerror(errno));
        exit(0);
    }

   while(1) {
        int retval = mq_send(q, "kardeshians\n", sizeof("kardeshians\n"), 1);

        if(retval == -1)    {
            printf("mq_open error %d  %s\n", errno, strerror(errno));
            exit(0);
        }
   }


}


void* consumer(void* arg)    {

    Log("consumer\n");
    char buff[64];
    mqd_t q = mq_open("/ytm", O_RDONLY);
    int prio;

    while(1)    {
        int retval =  mq_receive(q,buff,sizeof(buff), NULL);
        if(retval ==  -1)   {
            printf("read error %d  %s\n", errno, strerror(errno));
        } else {
            printf("got message : %s", buff);
        }
    }

}



int main()  {

    struct mq_attr attr;
    attr.mq_maxmsg = 10;
    attr.mq_msgsize = 32;
    mq_unlink ("/ytm");
    mqd_t queue = mq_open("/ytm", O_CREAT | O_RDWR, 0, &attr);


    pthread_t tid;
    pthread_create(&tid, 0 , producer, 0);
    pthread_create(&tid, 0 , consumer, 0);


    while(1);
}