getTaskCount might possibly see a decrease if your timing is
very bad, if called just before a worker runlock is unlocked,
and then again just after. Similarly, a task that has just been
removed from the workQueue but has not yet been started by a worker
will not be counted.

Probably we should just remove the "does not ever decrease".

    /**
     * Returns the approximate total number of tasks that have ever been
     * scheduled for execution. Because the states of tasks and
     * threads may change dynamically during computation, the returned
     * value is only an approximation, but one that does not ever
     * decrease across successive calls.
     *
     * @return the number of tasks
     */
    public long getTaskCount() {