A thread stress test
A thread stress test

(cherry picked from commit bc948ac1a5dca4d0a305a265de157d7505e4a4b2)

nedbat/coveragepy,nedbat/coveragepy,hugovk/coveragepy,hugovk/coveragepy,nedbat/coveragepy,nedbat/coveragepy,nedbat/coveragepy,hugovk/coveragepy,hugovk/coveragepy,hugovk/coveragepy