Make sure non-yielding threads don't interleave (#3914)
Make sure non-yielding threads don't interleave (#3914)


playi/pxt,switchinnovations/pxt,Microsoft/pxt,switch-education/pxt,switch-education/pxt,switchinnovations/pxt,switchinnovations/pxt,switch-education/pxt,playi/pxt,Microsoft/pxt,playi/pxt,switchinnovations/pxt,Microsoft/pxt,switch-education/pxt,Microsoft/pxt,switch-education/pxt,playi/pxt,Microsoft/pxt