revert changes to model viewer to fix thread leakage problem
revert changes to model viewer to fix thread leakage problem


Former-commit-id: 808ddc9abe722f2be2f1450cd126097ee2d250b8
julie-sullivan/phytomine,julie-sullivan/phytomine,julie-sullivan/phytomine,julie-sullivan/phytomine,julie-sullivan/phytomine,julie-sullivan/phytomine,julie-sullivan/phytomine