Log slow message processing

[willmcgugan]

If processing messages take longer than a fraction of a second, it can cause the UI to freeze.

This is usually the result blocking operations or cpu intensive work in a message handler. The solution is typically to do the work in a worker, but devs may not know to do that.

Given its a gotcha, I think Textual can do a little more to help.

I think what we should do is time how long a message has taken to process. If it is longer than, say 500ms, it should log a warning.

This should only be enabled in debug mode. The maximum time should be set in an environment variable.

I suspect, the best place to do this would be https://github.com/Textualize/textual/blob/main/src/textual/message_pump.py#L637

Requirements:

• Display warning for message handers that take a long time
• Enable in debug mode
• Add env var to set the time that produces a warning
• Should not add to much cpu work to message processing

Bonus points

Strictly following the above, would not produce a warning until the handler returns. If it takes 30 seconds, the dev would not see anything.

It would be great if long running message handlers produce a warning even before the handler returns. This would be a little trickier to implement. And it should be done in a way that doesn't slow down non-debug runs.

[Piechutowski]

Let me give this a shot 🙂

[willmcgugan]

Assigned to you. Let us know how it goes.

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