The test asserted one of two interleavings that are both correct, and
steered toward it with a 5 ms Thread.sleep. Under load the other
interleaving happened and main went red on a correct implementation.
The head start is now a latch counted down from inside the sweep's
guarded loop, so the ordering is guaranteed, not likely. Test file only;
the production guard is unchanged.
Verified here: 822 tests BUILD SUCCESS; 10/10 passes while a full clean
install ran in parallel; 5/5 failures with the guard removed, so the test
still catches the bug it exists for.
Closes#95
Dai Ha
a36b7ccd7c