How do I wait for a C# event to be raised?

Question

I have a Sender class that sends a Message on a IChannel:

public class MessageEventArgs : EventArgs {
  public Message Message { get; private set; }
  public MessageEventArgs(Message m) { Message = m; }
}

public interface IChannel {
  public event EventHandler<MessageEventArgs> MessageReceived;
  void Send(Message m);
}

public class Sender {
  public const int MaxWaitInMs = 5000;
  private IChannel _c = ...;

  public Message Send(Message m) {
    _c.Send(m);
    // wait for MaxWaitInMs to get an event from _c.MessageReceived
    // return the message or null if no message was received in response
  }
}

When we send messages, the IChannel sometimes gives a response depending on what kind of Message was sent by raising the MessageReceived event. The event arguments contain the message of interest.

I want Sender.Send() method to wait for a short time to see if this event is raised. If so, I'll return its MessageEventArgs.Message property. If not, I return a null Message.

How can I wait in this way? I'd prefer not to have do the threading legwork with ManualResetEvents and such, so sticking to regular events would be optimal for me.

Answer 1

Use a AutoResetEvent.

Gimme a few minutes and I'll throw together a sample.

Here it is:

public class Sender
{
    public static readonly TimeSpan MaxWait = TimeSpan.FromMilliseconds(5000);

    private IChannel _c;
    private AutoResetEvent _messageReceived;

    public Sender()
    {
        // initialize _c
        this._messageReceived = new AutoResetEvent(false);
        this._c.MessageReceived += this.MessageReceived;
    }

    public Message Send(Message m)
    {
        this._c.Send(m);
        // wait for MaxWaitInMs to get an event from _c.MessageReceived
        // return the message or null if no message was received in response


        // This will wait for up to 5000 ms, then throw an exception.
        this._messageReceived.WaitOne(MaxWait);

        return null;
    }

    public void MessageReceived(object sender, MessageEventArgs e)
    {
        //Do whatever you need to do with the message

        this._messageReceived.Set();
    }
}