jakesmith/HPCC-Platform — comment on commit c72cc47a99b4349003acd3c68e62a8306fafef57
File: system/jlib/jthread.cpp line 583
By jakesmith:

If another thread start()'s whilst one is join()'ing, yes the join thread could set ready and the persistent thread *could* be clearing the exception.
Though starting and joining of this object on different threads would be odd and very small window.
But might as well change JIC.