static synchronized void shutdownNow() {
      if (execService != null) {
        execService.shutdownNow();
      }
    }
Closes the executor service. This is called from
{@link PartitionedRegion#afterRegionsClosedByCacheClose(InternalCache)}
geode-core/src/main/java/org/apache/geode/internal/cache/PRQueryProcessor.java