Simplest way to do a fire and forget method in C#?

Question

I saw in WCF they have the [OperationContract(IsOneWay = true)] attribute. But WCF seems kind of slow and heavy just to do create a nonblocking function. Ideally there would be something like static void nonblocking MethodFoo(){}, but I don't think that exists.

What is the quickest way to create a nonblocking method call in c#?

E.g.

class Foo
{
    static void Main()
    {
        FireAway(); //No callback, just go away
        Console.WriteLine("Happens immediately");
    }

    static void FireAway()
    {
        System.Threading.Thread.Sleep(5000);
        Console.WriteLine("5 seconds later");
    }
}

Answer 1

ThreadPool.QueueUserWorkItem(o => FireAway());

Answer 2

An easy way is to create and start a thread with parameterless lambda:

(new Thread(() => { 
    FireAway(); 
    MessageBox.Show("FireAway Finished!"); 
}) { 
    Name = "Long Running Work Thread (FireAway Call)",
    Priority = ThreadPriority.BelowNormal 
}).Start();

By using this method over ThreadPool.QueueUserWorkItem you can name your new thread to make it easier for debugging. Also, don't forget to use extensive error handling in your routine because any unhandled exceptions outside of a debugger will abruptly crash your application:

Answer 3

To add to Will's answer, if this is a console application, just throw in an AutoResetEvent and a WaitHandle to prevent it exiting before the worker thread completes:

Using System;
Using System.Threading;

class Foo
{
    static AutoResetEvent autoEvent = new AutoResetEvent(false);

    static void Main()
    {
     ThreadPoolQueueUserWorkItem(new WaitCallback(FireAway), autoEvent);
     autoEvent.WaitOne(); // Will wait for thread to complete
    }

    static void FireAway(object stateInfo)
    {
     System.Threading.Thread.Sleep(5000);
     Console.WriteLine("5 seconds later");
     ((AutoResetEvent)stateInfo).Set();
    }
}

Answer 4

The simplest .NET 2.0 and later approach is using the Asynchnonous Programming Model (ie. BeginInvoke on a delegate):

static void Main(string[] args)
{
      new MethodInvoker(FireAway).BeginInvoke(null, null);

      Console.WriteLine("Main: " + Thread.CurrentThread.ManagedThreadId);

      Thread.Sleep(5000);
}

private static void FireAway()
{
    Thread.Sleep(2000);

    Console.WriteLine("FireAway: " + Thread.CurrentThread.ManagedThreadId );  
}

Answer 5

Calling beginInvoke and not catching EndInvoke is not a good approach. Answer is simple: The reason that you should call EndInvoke is because the results of the invocation (even if there is no return value) must be cached by .NET until EndInvoke is called. For example if the invoked code throws an exception then the exception is cached in the invocation data. Until you call EndInvoke it remains in memory. After you call EndInvoke the memory can be released. For this particular case it is possible the memory will remain until the process shuts down because the data is maintained internally by the invocation code. I guess the GC might eventually collect it but I don't know how the GC would know that you have abandoned the data vs. just taking a really long time to retrieve it. I doubt it does. Hence a memory leak can occur.

More can be found on http://haacked.com/archive/2009/01/09/asynchronous-fire-and-forget-with-lambdas.aspx