Question

I’m attempting to use the QueueUserWorkItem method on ThreadPool, however, I’m having some problems when I attempt to pass a delegate to the method. I imagine the problem with my code lies in the way I’ve setup my delegate, but I can’t seem to figure it out, even after searching around on google.

I’m creating my delegate like so:

public delegate void GetLatencyDelegate(Server server);

I’m attempting to loop through a list of servers and run the servers GetLatency method. Each time I loop through to a new server, a new thread should be ran from the pool to run the GetLatency method. The idea is that this should speed up the process. My code for this is the following:

            ThreadPool.SetMaxThreads(50, 50);

            foreach (Server server in serverList)
            {
                GetLatencyDelegate gld = new GetLatencyDelegate(server.GetLatency);
                ThreadPool.QueueUserWorkItem(new WaitCallback(gld));

            }

However, I get two errors. One being:

“No overload for ‘GetLatencyDelegate’ matches delegate
‘System.Threading.WaitCallback’

The other being:

‘No overload for ‘GetLatency’ matches delegate
‘Program.GetLatencyDelegate’

Answer 1

The first error occurs because the signature for WaitCallback is not the same as the signature for GetLatencyDelegate. The two should be identical.

The second error occurs because Server.GetLatency also does not have a signature compatible with GetLatencyDelegate: the former accepts no parameters, while the latter expects the Server instance to be passed in.

In fact there is absolutely no need to define GetLatencyDelegate in the first place. You can simply provide a lambda with a signature compatible with WaitCallback:

foreach (Server server in serverList)
{
    ThreadPool.QueueUserWorkItem(srv => ((Server)srv).GetLatency(), server);
}