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

[bugzilla-daemon at freedesktop.org]

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

            Bug ID: 97353
           Summary: Wayland lacks cross-process synchronisation
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: wayland
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: tomek.bury at gmail.com

Currently Wayland synchronisation model is build around an undefined behaviour,
which happens to work correctly with FOSS driver, but isn't guaranteed by
GL/EGL specifications. In other words a perfectly valid GL/EGL driver may not
work with Wayland.

The GL/EGL guarantees read-write synchronisation within a single context and
provides tools to synchronise multiple contexts within a single process, but
there are no guarantees or methods of achieving cross-process synchronisation,
except for Android fences, but those are Android-specific.

The only spec-compliant solution at the moment would be blocking CPU on the
compositor side (eglWaitClient() or glFinish()) before a buffer release event
is sent to the client. Alternatively, Wayland could create and mandate and
extension similar to EGL_ANDROID_native_fence_sync, where EGLSyncKHR objects
can be created from and converted to cross-process integer descriptors, that
are easy to send between client and compositor over Wayland protocol.

https://www.khronos.org/registry/egl/extensions/ANDROID/EGL_ANDROID_native_fence_sync.txt

Basing Wayland on an unspecified behaviour, where implementation detail of one
specific driver happens do deliver a desired result causes grief to other
driver maintainers where such behaviour isn't easy to achieve and, limits
Wayland adoption.

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