Question

How do I make a custom function that returns output and blocks until output is available? I’m thinking of something like Console.ReadLine(). Something like this:

var resp = Output(); //blocks until output is sent.
...
//returns a string once SendOutput is called and hands over the string.
public static string Output() { /* what goes here? */ }
//Is this function even needed? Can I just fire Output somehow?
private static string SendOutput(string msg) { /* what goes here? */ }
...
//Calls sendoutput with the string to send.
SendOutput(msg);

Basically I’m making a listener that is blocked until it gets data (like it would if calling console.readline), and I need the internal code to make the blocker.

Answer 1

What you want is for your blocking method call to be signalled when some other work has completed. A ManualResetEvent is a good way to achieve this behaviour; there are no loops, and the return is virtually instantaneous once the worker thread signals that it is complete.

class Program
{
    static void Main(string[] args)
    {
        Blocker b = new Blocker();
        Console.WriteLine(b.WaitForResult());
    }
}

public class Blocker
{
    private const int TIMEOUT_MILLISECONDS = 5000;
    private ManualResetEvent manualResetEvent;

    private string output;

    public string WaitForResult()
    {
        // create an event which we can block on until signalled
        manualResetEvent = new ManualResetEvent(false);

        // start work in a new thread
        Thread t = new Thread(DoWork);
        t.Start();

        // block until either the DoWork method signals it is completed, or we timeout (timeout is optional)
        if (!manualResetEvent.WaitOne(TIMEOUT_MILLISECONDS))
            throw new TimeoutException();

        return output;
    }

    private void DoWork()
    {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 10; i++)
        {
            sb.AppendFormat("{0}.", i);
        }
        output = sb.ToString();

        // worker thread is done, we can let the WaitForResult method exit now
        manualResetEvent.Set();
    }
}