xwm: replace LATE_SURFACE_ID

[Drakulix]

The current mechanism by which x11 window ids and their corresponding wl_surfaces are matched, may inject a LATE_SURFACE_ID client message similar to the original WL_SURFACE_ID message.

The problem with injecting this message is, that to do that it utilizes the same SyncSender, that is internally used by the X11Source. Given that this sender is sync and limited to 5 in-flight messages, queuing up additional messages from the same thread, that runs the calloop event loop and receives these messages may cause a deadlock. This can often be encountered when multiple windows are spawned by a client at the same time.

Instead of making the channel unbound this PR avoids the problem by changing the mechanism all together. Instead of injecting a message, the xwm state is accessed by an idle callback, which isn't prone to cause a deadlock.

[codecov-commenter]

Codecov Report

Base: 25.27% // Head: 25.25% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (8f4a697) compared to base (0630a22).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #869      +/-   ##
==========================================
- Coverage   25.27%   25.25%   -0.02%     
==========================================
  Files         130      130              
  Lines       20882    20882              
==========================================
- Hits         5277     5274       -3     
- Misses      15605    15608       +3     

Flag	Coverage Δ
wlcs-core	22.64% <100.00%> (ø)
wlcs-output	10.38% <0.00%> (ø)
wlcs-pointer-input	24.56% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
anvil/src/shell/mod.rs	41.40% <100.00%> (ø)
src/output.rs	66.89% <0.00%> (-2.03%)	⬇️

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[PolyMeilex]

LGTM

Kinda off topic, do you think Xwayland shell will help a bit with this convoluted event order dance?

[Drakulix]

LGTM

Kinda off topic, do you think Xwayland shell will help a bit with this convoluted event order dance?

Yes, because it eliminates the race. It requires a relatively recent Xwayland version though, which why I think we will need to keep the old code path for some time anyway.