CODEWITHSUNDEEP
cmultithreadingunixubuntupthreads
user2895478
user2895478

Reputation: 383

pthread_create gives an segmentation fault

I get a segmentation fault on line "pthread_t* tids = (pthread_t*) calloc(num_threads, sizeof(pthread_t));". I looked at the code for a day but cannot figure it out. I even delete all the content in the "child" function but it does not help.

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

    int sockfd, newsockfd, clilen;
    struct sockaddr_in serv_addr, cli_addr;
    int port_num, num_threads = 5;

    switch (argc) {
        case 3:
            num_threads = atoi(argv[2]);
        case 2:
            port_num = atoi(argv[1]);
            break;
        default:
            fprintf(stderr, "Usage: %s <port_number> <num_threads>\n", argv[0]);
            return -1;
            break;
    }
    queue_t *q;
    // the queue is unbounded if give a queue size of 0
    queue_init(&q, 0);  

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        perror("ERROR opening socket");
        return 1;
    }

    bzero((char*) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = INADDR_ANY;
    serv_addr.sin_port = htons((short) port_num);

    if (bind(sockfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) < 0)
        perror("ERROR on binding");

    listen(sockfd,5);

printf("numofthreads: %d\n", num_threads);
    pthread_t* tids = (pthread_t*) calloc(num_threads, sizeof(pthread_t));
    if (tids == NULL) {
        printf("ERROR: failed to allocate memory!\n");
    }

    int i;

    //for (i = 0; i < num_threads; i++) {
        if (pthread_create(&tids[i], NULL, child, NULL)) {
            perror("ERROR");
            close(newsockfd);
            return 1;
        }
    //}

    while(1) {

        clilen = sizeof(cli_addr);
            newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
            if (newsockfd < 0)
                    perror("ERROR on accept");
        queue_push(q, newsockfd);

            //close(s_info.newsockfd); TODO

    }

    //clean up
    clean_up(q);
    free(tids);
    free(output_dir);

    return 0;
}

Upvotes: 0

Views: 642

Answers (1)

jxh
jxh

Reputation: 70362

You are accessing an uninitialized variable, i:

    int i;

    //for (i = 0; i < num_threads; i++) {
        if (pthread_create(&tids[i], NULL, child, NULL)) {

Accessing an uninitialized variable results in undefined behavior. In this case, it could result in an invalid pointer passed in the first parameter to pthread_create(), causing it to crash when the function attempts to dereference the pointer.

Upvotes: 3

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