Qt quick 3d application is flickering and tearing when resizing window or changing running parameter

when running quick3d/screenspacereflections and virtualassistant applications, FPS is very low.  when normal running it is ok, but when resizing window or Go to Settings panel, and play with "Skybox rotation" slider, it is tearing and flickering.

Looks like processing event and graphics rendering are in two running in two separate threads,  the rendering parameters are allowed to change in the middle of rendering, which results in rendering with two different parameters in one frame.  the rendering parameter such as window size, rotation angle should be take effect after previous frame  and before next new frame rendering.