RFR: Empty task queues when cancelled partial GC

[Aleksey Shipilev]

On 03/20/2017 05:27 PM, Roman Kennke wrote:
> When partial GC gets cancelled, we need to empty the task queues.

Right! We also need to visit the terminator on that path...

> I also added a small check to verify this, even for release build
> (shuold we make this debug-only?)

Yes, wrap it up in ASSERT, and s/guarantee/assert/g

-Aleksey