update_from_render_element_states relies on strong_count to determine if Output is still valid

[ids1024]

smithay/src/backend/renderer/element/mod.rs

Lines 194 to 197 in 28417d2

	let has_valid_output = primary_scanout_output
	.as_ref()
	.map(|(current, _)| current.is_alive())
	.unwrap_or(false);

WeakOutput::is_alive() simply checks if the strong count is 0. In cosmic-comp I seem to be seeing an issue with it. Perhaps a strong reference is being held somewhere it shouldn't, either in Smithay or cosmic-comp.

Careful use of WeakOutput should avoid that, but I wonder if it would also be a good idea to explicitly track if the output is valid, instead of relying on reference count.

A compositor can set a compare callback that has an additional check to see if the old Output is still valid. But default_primary_scanout_output_compare won't do that. So this may be causing issues for any Smithay compositors that don't have a custom callback with some check for old removed/disabled outputs.