nerfstudio Adding lock for Viser Element callbacks

I added a wrapper around the viser element callback so the render thread is blocked while the callback is called to avoid crashing. I also added a lock in run_viewer.py so this issue is addressed for both ns-train and ns-viewer.

Test: I added time.sleep() in the callback and confirmed the render thread was blocked.

Apr 11 '24 15:04 Satvik1701

What kinds of crash did you see? I also experienced crashes (#3064 ) in the viser viewer.

Apr 11 '24 17:04 jb-ye

This PR fixes a bug with a race condition in custom viewer element callbacks (eg a ViewerButton which renders the current view), previously this might clash with the standard rendering thread and crash the callback or main renderer.

Apr 11 '24 17:04 kerrj

@kerrj I found this PR impacts the experience of ns-viewer when training gaussian splatting. The delay when I rotate the scene is so long that basically disallow me to interact with the scene. Do you observe similar issue?

Apr 30 '24 21:04 jb-ye

That's odd I don't notice any difference. In fact it shouldn't affect things since the only code that was added to the lock was viser element callbacks, which splatfacto doesn't have any of.

May 01 '24 00:05 kerrj