Code Review 7091003: ScheduledExecutorService never executes Runnable with corePoolSize of zero

[David Holmes]

Sorry Doug/Chris I should have seen this previously, the order here is 
wrong:

1552     void ensurePrestart() {
1553         int wc = workerCountOf(ctl.get());
1554         if (wc == 0)
1555             addWorker(null, false);
1556         else if (wc < corePoolSize)
1557             addWorker(null, true);
1558     }

this will always mark the first worker as non-core even if the 
corePoolSize is > 0. It needs to be swapped

      void ensurePrestart() {
          int wc = workerCountOf(ctl.get());
          if (wc < corePoolSize)
              addWorker(null, true);
          else if (wc == 0)  // corePoolSize must be 0
              addWorker(null, false);
      }

David
-----

On 23/09/2011 2:54 AM, Chris Hegarty wrote:
> This change is coming from Doug Lea's CVS and I've already review it.
>
> It seems that in the re-work that was done for Java 7 we dropped this
> corner case.
>
> STPE.delayedExecute will add the task to the work queue and invoke
> prestartCoreThread. But prestartCoreThread checks for the worker count
> (0) being less than corePoolSize (0) and as that is not the case nothing
> happens. So we have a task in the queue but no thread waiting to execute
> it.
>
> For STPE when the queue is not empty there must always be at least one
> thread waiting on the queue.
>
> http://cr.openjdk.java.net/~chegar/7091003/webrev.00/webrev/
>
> -Chris.