When calling glfwCreateWindow() the call blocks forever. This problem looks to be very similar to one in Ubuntu/Unity due to wrong handling of _NET_REQUEST_FRAME_EXTENTS. Please see accordant bug for GLFW:
Please provide a reproducer
The spec  states:
"A Client whose window has not yet been mapped can request of the Window Manager an estimate of the frame extents it will be given upon mapping. To retrieve such an estimate, the Client MUST send a _NET_REQUEST_FRAME_EXTENTS message to the root window. The Window Manager MUST respond by estimating the prospective frame extents and setting the window's _NET_FRAME_EXTENTS property accordingly. The Client MUST handle the resulting _NET_FRAME_EXTENTS PropertyNotify event. So that the Window Manager has a good basis for estimation, the Client MUST set any window properties it intends to set before sending this message. The Client MUST be able to cope with imperfect estimates."
The code  does:
When the root window receives _NET_REQUEST_FRAME_EXTENTS message, it sends a client message _NET_FRAME_EXTENTS with the default decorations size.
AFAICT, xfwm4 code matches the standard.
OK, I know what happens, since the window is not yet mapped, it is unknown to the WM which fails determine the root window and ignore the request.
I shall post a fix later.
Thank you very much Olivier!
If you need a short demo code to test, I can attach it here.
No thanks, it's fine, I can reproduce with glfw tests included on the source package.
A fix for this has been pushed in both master and xfce-4.12 branches.
Thank you very much Olivier for the fast help! I've just tested your fix and it works perfectly. Hope to see official patch release soon...
How long until this patch ends up in ppa:xubuntu-dev/xfce-4.12 ?
*** Bug 11705 has been marked as a duplicate of this bug. ***