protected void complete() {
        this.iteration.decrementAndGet();
        this.previousMap = this.currentMap;
        this.memoryKeys.values().stream().filter(MemoryComputeKey::isTransient).forEach(computeKey -> this.previousMap.remove(computeKey.getKey()));
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/process/computer/TinkerMemory.java