UDP with another software error

Question

I am using IPG CarMaker and am trying to export the data to another machine using UDP, real time. I am referring to http://www.codeproject.com/Articles/11740/A-simple-UDP-time-server-and-client-for-beginners. I want to send the position of the car whenever the client requests it. Now I have included the above code into CarMakers main loop which has a timestep of 1 ms. There is no problem while I build the program (using Visual Studio 2010). But when I try running simulations in CarMaker, the following line causes the simulation to get timed out:

bytes_received = recvfrom(sd, buffer, BUFFER_SIZE, 0, (struct sockaddr *)&client, &client_length);

As a result my simulation does not start at all! Is it because I don't have a client running alongside at the same time? Please help! The code in the main loop is as follows:

User_DrivMan_Calc (double dt) { client_length = (int)sizeof(struct sockaddr_in);

bytes_received = recvfrom(sd, buffer, BUFFER_SIZE, 0, (struct sockaddr *)&client, &client_length);

if (bytes_received < 0)
{
    fprintf(f, "Could not receive datagram.\n");
    closesocket(sd);
    WSACleanup();
    exit(0);
}

/* Check for time request */

if (strcmp(buffer, "GET DISTANCE\r\n") == 0)
{
    /* Get current time */
    current_time = time(NULL);
    d = Car.Distance;       
    /* Send data back */
    if (sendto(sd, (char *)&d, (int)sizeof(d), 0, (struct sockaddr *)&client, client_length) != (int)sizeof(d))
    {
        fprintf(f, "Error sending datagram.\n");
        closesocket(sd);
        WSACleanup();
        exit(0);
    }
}

return 0;

}

Answer 1

That is a blocking read, i.e. it won't return from the function until the read has succeeded.

If no data is waiting, it will block for a very long time.

You need to use e.g. select() to detect when data is available, or make the socket non-blocking.

Also, if your packet rate is going to be 1,000 Hz, that is (way) too fast for this kind of application, in general.