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: [email protected]
Reporter: [email protected]
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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