code: function(docs) {
          setTimeout(function() {
              self.events.emit('processedBatch', {
                  size: docs.length,
                  docs: totalDocs,
                  batches: numThreads,
                  index: finished
              });
          });
  
          for (var j = 0; j < docs.length; j++) {
              docFeatures[docs[j].index] = docs[j].features;
          }
      }
docs: Called when a batch completes processing