在线程中使用共享内存

Question

Hi i want to implement a client-server program that communicates with each other via shared memory. in the server side i have two threads. a writer thread and a reader thread. the writer thread puts some data into the queue and the reader thread reads from it and passes the data to the client side...

here is my reader thread ... the problem is that my two threads are created successfully but it does not get into the while loop i have specified in the thread routine... right now my question is: is it possible to work with shared memory in a thread routine when the thread is called?

    void *reader_thread(void * id)
    {
        .....

        shm_addr = shmat(shm_id,NULL,0);

        if(shm_addr==(void *)-1)
        {
                    perror("shmat error");
            exit(1);
        }

        while (1)
        {   
            printf("Here in thread reader!");
            sem_wait(&queue_t->full);
            sem_wait(&queue_t->mutex);
            if (queue_t->tail != queue_t->head)
            {
                   memmove(imgPath,queue_t->imgAddr[queue_t->head],strlen(queue_t->imgAddr[queue_t->head])-1);
                imgPath[strlen(queue_t->imgAddr[queue_t->head])-1] = '\0';
                queue_t->head = (queue_t->head + 1) % QUEUE_SIZE;
             }  
            sem_post(&queue_t->mutex);
            sem_post(&queue_t->empty);

            ...
                sem_wait(&shared->shm_sem);
                memset(shm_addr,0,SHMSZ);
                memcpy(shm_addr, &imgPath, sizeof(imgPath));    
                sem_post(&shared->shm_sem);  

        }   
        return 0;
    }

///////////////////////////////


int main(int argc , char *argv[])
{

    pthread_t writer_t, reader_t;

    queue_t = (struct Queue*) malloc(sizeof(Queue));
    queue_t->head = 0;
    queue_t->tail = 0;

    sem_init(&queue_t->empty, 0, QUEUE_SIZE);
    sem_init(&queue_t->full, 1, 0);
    sem_init(&queue_t->mutex, 1, 1);

    shared = (struct shared_mem*) malloc(sizeof(shared_mem));
    sem_init(&shared->shm_sem, 1, 1);   

    int shmid;
    key_t key; 
    char *shm_addr; 
    key=1234;

    //Create the segment and set permissions.
    if ((shmid = shmget(key, SHMSZ, IPC_CREAT | 0666)) < 0)
    {
        perror("shmget error");
        if(errno==EEXIST)
                {
                        fprintf(stderr,"shared memory exist... ");
                        exit(1);
                }
    }
    fprintf(stdout,"shared mem created with id: %d\n",shmid);

    //Now we attach the segment to our data space.   
    if ((shm_addr = shmat(shmid, NULL, 0)) == (char *) -1)
    {
        perror("shmat error");
        exit(1);
    }

    // Zero out memory segment
    memset(shm_addr,0,SHMSZ);

    if( pthread_create( &reader_t , NULL , reader_thread , &shmid) < 0)
    {
        perror("could not create reader thread");
        return 1;
    }

    pthread_detach(reader_t);
    puts("reader thread assigned");

    if( pthread_create( &writer_t , NULL , writer_thread , NULL) < 0)
    {
        perror("could not create writer thread");
        return 1;
    }
    pthread_detach( writer_t);
        puts("writer thread assigned");

    //if(shmdt(shm_addr) != 0)
          //      fprintf(stderr, "Could not close memory segment.\n");
    shmctl(shmid,IPC_RMID,NULL);
    return 0;
}

Answer 1

the previous problem had resolved... i replaced pthread_detach with pthread_join and put of at the end of main. but rigt now i encountered segfault at client Side: client get segmentation fault when attach to shared memory