def nextResult
      result = nil
      @mutex.synchronize do
        result = @results.shift
        @progressMutex.synchronize{ @requestProgress.delete result.requestId } if result
      end
      result
    end
def nextResult
      result = nil
      @mutex.synchronize do
        result = @results.shift
        @progressMutex.synchronize{ @requestProgress.delete result.requestId } if result
      end
      result
    end
Result retrieval. Returns the next result, or nil if none are ready.
 The results that are returned are PieceIOWorker::Result objects.
 For readBlock operations the data property of the result object contains
 the block.