What's the difference between QueueUserWorkItem() and BeginInvoke(), for performing an asynchronous activity with no return types needed

Question

Following on from my BeginInvoke()/EndInvoke() question, are there major differences in performance/anything else between Delegate.BeginInvoke() and using QueueUserWorkItem() to invoke a delegate asynchronously?

Answer 1

The main thing I can think of with QueueUserWorkItem is that you have to use the WaitCallback delegate type, which looks tricky if you already have a SomeRandomDelegate instance and some args. The good news is that you can fix this with a closure:

ThreadPool.QueueUserWorkItem(
    delegate { someDelegate(arg1, arg2); }
);

This pattern also ensures you get proper strong typing at compile time (unlike passing an object state arg to QueueUserWorkItem and casting it in the target method). This pattern can also be used when calling methods directly:

ThreadPool.QueueUserWorkItem(
    delegate { SomeMethod(arg1, arg2); }
);

Obviously, without an EndInvoke equivalent, you also can't get a return value back out unless you call a method / raise an event / etc at the end of your method... on a related note, you need to be careful with exception handling.

Answer 2

http://blogs.msdn.com/cbrumme/archive/2003/07/14/51495.aspx

says:

"One surprising fact is that this is also why Delegate.BeginInvoke / EndInvoke are so slow compared to equivalent techniques like ThreadPool.QueueUserWorkItem (or UnsafeQueueUserWorkItem if you understand the security implications and want to be really efficient). The codepath for BeginInvoke / EndInvoke quickly turns into the common Message processing code of the general remoting pathway."