present: Send a PresentConfigureNotify event for destroyed windows

This is a fix for a deadlock case, where the client ends up blocked waiting for a Present event that will never come because the window was destroyed.

The fix as written is a bit hacky. Clients will simply be sent this new kind of event rather than selecting for a new PresentDestroyNotify, and the values in the event run the risk of making the client do something "illegal", 0x0 isn't a valid size for example. In practice I expect it's fine, most clients are not expecting to survive their GLXWindow being ripped out from under them, which means this simply promotes a deadlock-on-exit to a crash-on-exit.

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Posting this for discussion, I don't have a ton of time to follow up on this and I don't really care whether this is sent unconditionally or needs a whole new protocol bump. Frankly if I were bumping the protocol this is a pretty half-assed solution and #1428 is what I'd rather see. Regardless, someone decide and push this across the finish line please.

This seems absolutely terrible, but yeah, I can't really think of a better solution. Half-rewriting XCB is 'better' from some point of view, but not from the point of view where things ever actually ship.

As discussed before, using another field of the event which isn't already used by Mesa wouldn't risk regressions.

this simply promotes a deadlock-on-exit to a crash-on-exit

Closing a window doesn't imply the application will exit. For applications not affected by the deadlock, this could turn closing one of its windows into a crash.

Ugh, looks like the commit log is just stale.

pixmap_flags is already not used by Mesa, yes.

EDIT: I suppose there's no real reason to zero out the window geometry, so the 0x0 thing isn't necessary. But the new pixmap_flags, that we should definitely keep.

But the new pixmap_flags, that we should definitely keep.

Yep, that alone should suffice.

Proposal for new commit log:

This enables fixing a deadlock case on the client side, where the client
ends up blocked waiting for a Present event that will never come because
the window was destroyed. The new PresentWindowDestroyed flag allows the
client to avoid blocking indefinitely.

Done.

• Rephrased the commit message
• Renamed PresentPixmapDestroyed to PresentWindowDestroyed
• Keep the original window size + border width + sibling intact when sending the PresentWindowDestroyed flag

changed milestone to %xwayland-23.1.0

mentioned in issue #1426 (closed)

added 146 commits

• 2ea05583...098fcedf - 145 commits from branch xorg:master
• 74a93b70 - present: Send a PresentConfigureNotify event for destroyed windows

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74a93b70 is

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>

(assuming there's no time to get the new flag into a xorgproto release before creating the xwayland-23.1 branch)

FWIW, it's an #ifndef PresentWindowDestroyed so we can land the flag in xorgproto later.

I've filed xorg/proto/xorgproto#43 for this, so we do not forget.

added 1 commit

• 462b0603 - present: Send a PresentConfigureNotify event for destroyed windows

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mentioned in issue xorg/proto/xorgproto#43

approved this merge request

mentioned in merge request mesa/mesa!21339 (merged)

approved this merge request

New version looks great, thanks!

Thanks, let's merge it then!

added present label

merged

mentioned in issue mesa/mesa#9152 (closed)