C# Call a method in a new thread

If you actually start a new thread, that thread will terminate when the method finishes:

Thread thread = new Thread(SecondFoo);
thread.Start();

Now SecondFoo will be called in the new thread, and the thread will terminate when it completes.

Did you actually mean that you wanted the thread to terminate when the method in the calling thread completes?

EDIT: Note that starting a thread is a reasonably expensive operation. Do you definitely need a brand new thread rather than using a threadpool thread? Consider using ThreadPool.QueueUserWorkItem or (preferrably, if you're using .NET 4) TaskFactory.StartNew.

Does it really have to be a thread, or can it be a task too?

if so, the easiest way is:

Task.Factory.StartNew(() => SecondFoo())

Once a thread is started, it is not necessary to retain a reference to the Thread object. The thread continues to execute until the thread procedure ends.

new Thread(new ThreadStart(SecondFoo)).Start();