[c#] How to check if Thread finished execution

It depends on how you want to use it. Using a Join is one way. Another way of doing it is let the thread notify the caller of the thread by using an event. For instance when you have your graphical user interface (GUI) thread that calls a process which runs for a while and needs to update the GUI when it finishes, you can use the event to do this. This website gives you an idea about how to work with events:

http://msdn.microsoft.com/en-us/library/aa645739%28VS.71%29.aspx

Remember that it will result in cross-threading operations and in case you want to update the GUI from another thread, you will have to use the Invoke method of the control which you want to update.