static void service_shm(int segment_id) {
    char *file;
    char *response;
    int fd, len;
    struct stat     sb;
    shm_thread_t *shm = &shm_thread[segment_id];


    pthread_cond_wait(&shm->cond, &shm->mutex);
    file = strdup(&shm->data[1]);

    strdecode(file, file);
    if (file[0] == '\0')
        file = "./";
    len = strlen(file);
    if (file[0] == '/' || strcmp(file, "..") == 0 || strncmp(file, "../", 3) == 0 || strstr(file, "/../") != (char *) 0 || strcmp(&(file[len - 3]), "/..") == 0) {
        free(file);
        response = make_error(400, "Bad Request", (char *) 0, "Illegal filename.");
        write_shm(segment_id, response, strlen(response));
        free(response);
        close_shm(segment_id);
        return;
    }
    if (stat(file, &sb) < 0) {
        free(file);
        response = make_error(404, "Not Found", (char *) 0, "File not found.");
        write_shm(segment_id, response, strlen(response));
        free(response);
        close_shm(segment_id);
        return;
    }
    fd = open(file, O_RDONLY, 0);
    if (fd < 0) {
        free(file);
        response = make_error(403, "Forbidden", (char *) 0, "File is protected.");
        write_shm(segment_id, response, strlen(response));
        free(response);
        close_shm(segment_id);
        return;
    }

    free(file);
    response = make_headers(200, "Ok", (char *) 0, get_mime_type(file), sb.st_size, sb.st_mtime);
    write_shm(segment_id, response, strlen(response));
    free(response);

    do {
        len = read(fd, shm->data, SHM_BUF_SIZE);
        shm->data_size = len;
        pthread_cond_signal(&shm->cond);
        pthread_cond_wait(&shm->cond, &shm->mutex);
    } while (len > 0);

    close(fd);
    close_shm(segment_id);

}

static void write_shm(int segment_id, char *data, int len) {
    shm_thread_t *shm = &shm_thread[segment_id];
    shm->data_size = len < SHM_BUF_SIZE ? len : SHM_BUF_SIZE;
    memcpy(shm->data, data, shm->data_size);
    pthread_cond_signal(&shm->cond);
    pthread_cond_wait(&shm->cond, &shm->mutex);
}

static void close_shm(int segment_id) {
    shm_thread_t *shm = &shm_thread[segment_id];
    shm->data_size = 0;
    shm->done = 1;
    pthread_cond_signal(&shm->cond);
    pthread_cond_wait(&shm->cond, &shm->mutex);
}