The status field holds run control status bits packed into a single int to ensure atomicity. Status is initially zero, and takes on nonnegative values until completed, upon which it holds (sign bit) DONE, possibly with ABNORMAL (cancelled or exceptional) and THROWN (in which case an exception has been stored). Tasks with dependent blocked waiting joiners have the SIGNAL bit set. Completion of a task with SIGNAL set awakens any waiters via notifyAll. (Waiters also help signal others upon completion.)
Cancels, ignoring any exceptions thrown by cancel. Used during worker and pool shutdown. Cancel is spec'ed not to throw any exceptions, but if it does anyway, we have no recourse during shutdown, so guard against this case.