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Smithay / calloop

A callback-based Event Loop
MIT License
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Need to call callback at start of dispatch #65

Closed Molytho closed 2 years ago

Molytho commented 2 years ago

WaylandSource of Client-Toolkit needs a way to run code when starting a dispatch cycle (equivalent of idle callbacks) for a proper implementation.

The background can be found here: https://github.com/Smithay/client-toolkit/issues/212

elinorbgr commented 2 years ago

Given the context around the need, I think this would be best done by adding a method to the EventSource trait that is invoked before the start of a poll cycle.

And probably adjust the error handling to be signaled to the event source as well.

This way the user of an event source doesn't need to manually plumb some source-specific logic.

Molytho commented 2 years ago

Sounds good to me but breaks API and is mostly useless to other users of calloop. I thought about it and maybe we could introduce a new trait which provides the interface to the methods and add a method to EventSource which is called on insertion (which I imagine is more useful to other users) and allows to add an event handling object to the queue. This on the other side is more complex in sense of borrowing and lifetime.

elinorbgr commented 2 years ago

Actually I forgot that the Readiness struct already contains an error flag, and I don't think epoll can tell use more than what can already be checked in the callback, so that one is a non-issue.

Adding new methods to EventSource is not breaking, as long a those methods have a default implementation, which would be simply to do nothing in this case.