c# - Why does asynchronous delegate method require calling EndInvoke?

Question

Why does the delegate need to call the EndInvoke before the method fires? If i need to call the EndInvoke (which blocks the thread) then its not really an asynchronous call is it?

Here is the code im trying to run.

class Program
    {
        private delegate void GenerateXmlDelegate();

        static void Main(string[] args)
        {
            GenerateXmlDelegate worker = new GenerateXmlDelegate(GenerateMainXml);
            IAsyncResult result = worker.BeginInvoke(null, null);
        }

        private static void GenerateMainXml()
        {
            Thread.Sleep(10000);
            Console.WriteLine("GenerateMainXml Called by delegate");
        }
    }

Answer 1

The reason you need to call EndInvoke is to avoid memory leaks; .Net will store information about the function's result (or exception) until you call EndInvoke.

You can call EndInvoke in the completion handler that you give to BeginInvoke and retain the asyncronous nature.

EDIT:

For example:

class Program {
    private delegate void GenerateXmlDelegate();

    static void Main(string[] args) {
        GenerateXmlDelegate worker = new GenerateXmlDelegate(GenerateMainXml);
        IAsyncResult result = worker.BeginInvoke(delegate {
            try {
                worker.EndInvoke();
            } catch(...) { ... }
        }, null);
    }

    private static void GenerateMainXml() {
        Thread.Sleep(10000);
        Console.WriteLine("GenerateMainXml Called by delegate");
    }
}

---

If you want to fire an async call and forget about it, you can use the ThreadPool, like this:

ThreadPool.QueueUserWorkItem(delegate { GenerateMainXml(); });