What's wrong with calling Invoke, regardless of InvokeRequired?

Question

I\'ve seen the common setup for cross threading access to a GUI control, such as discussed here: Shortest way to write a thread-safe access method to a windows forms control

Answer 1

The issue is that GUI controls have a requirement that only code executing on the same thread that was used to instantiate the GUI control can access the GUI control. The reasons behind this requirement are tied to the way that Windows is architected. Suffice to say, it would very difficult to change this.

The InvokeRequired checks the identity of the current executing thread against the identity of the instantiating thread. If they are the same, the code can freely interact with the control. If not, the code must marshal the data across from the current thread to the instantiating thread. This is a slow and costly process and is to be avoided if at all possible. Your code will work if you always invoke and it may be that you will not notice the performance hit, but this scenario is going to be increasingly common as multi-core systems come into use. It is best not to create code "knots" that have to be undone later.