suppose there is a piece of code on the server side with two threads open, one to process the client connection and one to read the message sent by the client.

m_fd = socket(AF_INET, SOCK_STREAM, 0);

bind(...);
listen(...);

pid_t pid;
while (1)
{
    m_client_fd = accept(m_server_fd, (sockaddr*)&client_addr, &len);

    pid = fork();

    if (pid == 0) // 
    {
         close(m_fd); // 

         do_read_from_client(m_client_fd); // m_client_fd

         close(m_client_fd); // 
         exit(EXIT_SUCCESS);
    }
    else
    {
         close(m_client_fd); // 
    }
}

/*************************************************/

close(m_fd); // 

/****************************************************************/

how to turn off the file descriptor fd, correctly when it comes to multithreading?