[Haskell-cafe] Windows: how to perform cleanup actions when the console window closes

Peter Dedecker nectarien at gmail.com
Fri Apr 6 12:46:45 UTC 2018

So I looked at this some more, and determined a few things:

- Ctrl-C did not do anything in the original program because the main
thread was blocked on a socket accept() call, which seemingly could
not be interrupted for an asynchronous exception.

- I fixed this by having the main thread initialize everything, then
running the main body of code in an async and waiting on that.
Apparently this wait is interruptible, so Ctrl-C works, bracket nicely
cleans up, and the application exits. Good!

- Then I added a console handler to capture 'close' events. Here is
the code for the handler:
f mainThreadID event =
            case event of
                ControlC -> putStrLn "HANDLER" >> throwTo mainThreadID
                Break    -> putStrLn "HANDLER" >> throwTo mainThreadID
                Close    -> putStrLn "HANDLER" >> throwTo mainThreadID
ThreadKilled >> threadDelay maxBound
                _        -> pure ()

Where the 'threadDelay' call serves simply to give the main thread time to exit.
This works fine for ControlC and Break, but fails for Close: the
program exists immediately, and no cleanup is run.

So I still haven't solved how to clean up when the window close button
is hit. Any thoughts?


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