Android UI not responding when loading larger GLB model

[mbalajee]

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Describe the bug When loading larger models (over 8K entities) ModelViewer#loadModelGlb blocks the UI. Calling this function in a different thread results in This thread has not been adopted when executing ResourceLoader::Impl::computeTangents

Engine has been created from main thread so as per the below comment in Engine.cpp,

    // we're assuming we're on the main thread here.
    // (it may not be the case)
    mJobSystem.adopt();

only the thread from which the Engine is created will be adopted by the JobSystem which eventually blocks the UI when loading larger model

To Reproduce Steps to reproduce the behavior: Loading a larger model hangs the entire UI, can't exit out of the screen

Expected behavior UI should not be blocked

Desktop (please complete the following information):

• OS: Android

  FEngine resolved backend: OpenGL
  QUALCOMM build                   : 8e5405b, I57aaec3440
  Build Date                       : 05/21/21
  OpenGL ES Shader Compiler Version: EV031.32.02.10
  Local Branch                     : mybranchebba1dbe-451b-f160-ac81-1458d0b52ae8
  Remote Branch                    : quic/gfx-adreno.lnx.1.0.r135-rel
  Remote Branch                    : NONE
  Reconstruct Branch               : NOTHING
  Build Config                     : S P 10.0.7 AArch64
  Driver Path                      : /vendor/lib64/egl/libGLESv2_adreno.so
  PFP: 0x016ee190, ME: 0x00000000
  [Qualcomm], [Adreno (TM) 630], [OpenGL ES 3.2 V@0502.0 (GIT@8e5405b, I57aaec3440, 1621601959) (Date:05/21/21)], [OpenGL ES GLSL ES 3.20]

Smartphone (please complete the following information):

• Device: OnePlus 6T/6GB RAM
• OS: Android 11

Additional context Sorry couldn't attach the glb file as it is confidential

[mbalajee]

UI is not blocked when I create the ModelViewer instance (& so the Engine instance) in Executors.newSingleThreadExecutor() & call modelViewer.render from the same executor. Is this the right way to unblock UI or is there a downside in creating ModelViewer in a non-main thread?

[mbalajee]

Oh when I back out of the screen I get this error,

Precondition
in shutdown:444
reason: Engine::shutdown() called from the wrong thread!

because ModelViewer destroys the view in addOnAttachStateChangeListener so I guess it is not as straightforward as operating modelViewer on a non-ui thread

@romainguy would you recommend maintaining a copy of ModelViewer ?