ANGLE: Threaded render-controlled windows crash with quick windows

Qt Quick applications crash under such circumstance:

• Using ANGLE OpenGL back-end
• Using threaded render control to draw quick windows
• Using standard quick windows

Threaded render controlled windows works well with other quick windows on desktop OpenGL but ANGLE doesn't.

I think it could be a potential thread synchronization issue because the single thread render controlled windows also works well with other quick windows on ANGLE back-end.

The attachment is a minimal project to reproduce this issue, which is modified from rendercontrol example and I only add a standard quick window in demo.qml.