Wayland client library thread safety

[Arnaud Vrac]

Hello everyone,

I am hitting a bug when using Qt5 and wayland on an embedded platform,
for which I have written a custom EGL backend. The problem is that Qt5
(QtQuick2 actually) renders in a separate thread, when the wayland
display has been created in the main thread. I know there is a patch
for "thread affinity" in qtwayland to solve this, but it is wrong and
breaks other clients.

Since it is required from the EGL spec to be able to render in
multiple threads, how can this be solved ? Does the wayland backend
for mesa support this properly ? I don't see how it can work since
even writes in the connection queue are not protected.

Here is a crude extract from my EGL backends where wayland can fail
because of thread concurrency:

- SwapBuffers:

while (!swap_done) {
  wl_display_flush()
  // wait frame callback
  wl_display_iterate(WL_DISPLAY_READABLE)
}

wl_surface_frame()
wl_surface_attach()
wl_surface_damage()
lock_back_buffer()
swap_buffers()

- GetBuffers (called on makeCurrent or at the first gl call after swap)

while (no_buffer_unlocked)
  wl_display_flush()
  // wait for a buffer to be released
  wl_display_iterate(WL_DISPLAY_READABLE)
}

Thanks for your help,

-- 
rawoul