How to Interrupt the UI thread

Question

I'm working on a simulation model that iterates over time steps. At times when the model results start to go South, I want to be able to click on a button to halt the iteration. However, if my testing is correct, when the iteration is running in the UI thread, the Button.Click event is not actuated because the thread is busy iterating. Is that correct? Is there a way to interrupt the UI thread with a button click when the thread is really busy?

One way to handle this problem is to create a Task using the Task Parallel Library to do the computationally-heavy iterations. I'm starting to work on this approach in case there is no way to interrupt the UI thread but I thought I'd check here to make sure I'm not missing a simpler approach.

Answer 1

The problem with your idea to interrupt your calculations on the UI thread is that it requires the cooperation of the UI thread, which is already slammed doing your calculating. For the UI thread to be able to process your button click the calculating needs to stop so the thread can go back to processing UI events. That means saving your progress so you can pick up where you left off later.

This kind of pausing and resuming seems likely to be more trouble than spinning the computation off into its own thread, it is not totally undo-able (the Netscape browser that JWZ developed worked like this, in a single thread), but the reason the multithreaded approach is encouraged is because it's the way that requires the least work, and keeps your calculation code the most focused on the domain and the least chopped up.

If you put the computation in its own thread then the UI thread will be responsive, the OS will make sure both threads get to run. You can make the calculation check for interruption periodically, you can have a progress bar with a cancel button, and you won't have to worry about stopping work to process UI events.

I'm assuming a UI where you have a single event dispatch thread that is responsible for handling UI events. This is how Swing works in Java and it's a popular choice for lots of GUI toolkits because multithreaded solutions are susceptible to deadlocks (events coming from the user will acquire locks in a different order than events coming from the back end). You can specify tags for language and platform to get more relevant answers.