[Wayland-bugs] [Bug 97353] Wayland lacks cross-process synchronisation

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97353

--- Comment #14 from Tomek Bury <tomek.bury at gmail.com> ---
(In reply to Daniel Stone from comment #13)
> (In reply to Kristian Høgsberg from comment #12)
> > Which compositor is this?

QtWayland as of Qt 5.7.

Back in the Qt 5.4 days (ish) that compositor was actually creating and
destroying EGL images every frame, but that days are gone. The latest and
greatest creates EGL image once and reuses it for the lifetime of a client.

> > unrefs the EGLImages when a new wl_buffer is attached, but maybe there's
> > some subtlety in the ref-counting there.

I don't know, although Qt implementation also uses ref counting to decide when
to end a wl_buffer_release.

> I'd equally consider any compositor which doesn't do this to be broken.
> Weston to the best of my knowledge (and a quick check) does destroy and
> recreate.

Again, I don't know. I didn't see anywhere such requirement or promise that EGL
image wrapping wl_buffer is guaranteed to be destroyed before buffer release.
If that was the case "release" would be a responsibility of a platform
implementation, the same way the "attach" is. To my untrained eye
wl_buffer_release() and eglImageDestroy() over 2 independent and asynchronous
channels looks like asking for trou^H^H^H^H race condition.

> You're very right that this should be documented better. I'm not sure if the
> Khronos specs are the best place, or a document in the Wayland repository
> itself. Can we take this bug as one request for explicit fencing support
> (being actively pursued), and another one to document the EGL platform
> requirements for both driver implementations and compositors?

Thanks. Would you like me to create 2 dependent Mozilla tickets?

-- 
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/wayland-bugs/attachments/20160816/e35a374a/attachment.html>