RFR: Force termination logic is inverted

[Aleksey Shipilev]

On 10/16/2018 04:47 PM, Zhengyu Gu wrote:
> When should_force_termination() returns true, termination should be terminated even there are
> remaining tasks. Current logic does the opposite, it jumps right back for stealing works, e.g.
> returning false.
> Which means, it actually drains task queues, instead of leaving tasks there for degen cycle.
> 
> Weberev: http://cr.openjdk.java.net/~zgu/shenandoah/force_termination/webrev.00/

Ugh. That condition is really hard to understand, no surprises there are bugs. It took me several
minutes to grasp it. I finally convinced myself it is correct by rewriting it into:

    bool force = (terminator != NULL) && terminator->should_force_termination();
    bool exit  = (terminator != NULL) && terminator->should_exit_termination();
    if ((!force && peek_in_queue_set()) || exit) {
      _offered_termination --;
      _blocker->unlock();
      return false;
    }

Consider doing this instead?

Thanks,
-Aleksey