public int size(PartitionedRegion pr, int bucketId) throws ForceReattemptException {
    throw new RuntimeException("This method(size)is not supported by ParallelGatewaySenderQueue");
  }
shutdown this thread and the caller thread will join this thread
geode-core/src/main/java/org/apache/geode/internal/cache/wan/parallel/ParallelGatewaySenderQueue.java