Github user dkuppitz commented on the issue:
https://github.com/apache/tinkerpop/pull/485
Here's an example that shows how it produces the expected result and still
tries to use `barrier()`'s as often as possible:
```
gremlin> g = TinkerFactory.createModern().traversal()
==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
gremlin> g.V().store("a").both().sideEffect(select("a").sideEffect {println
"Expect Intermediate: " + it.get()}).barrier().
......1> out().out().sideEffect(select("a").sideEffect {println "Expect
Final: " + it.get()})
Expect Intermediate: [v[1]]
Expect Intermediate: [v[1]]
Expect Intermediate: [v[1]]
Expect Intermediate: [v[1], v[2]]
Expect Intermediate: [v[1], v[2], v[3]]
Expect Intermediate: [v[1], v[2], v[3]]
Expect Intermediate: [v[1], v[2], v[3]]
Expect Intermediate: [v[1], v[2], v[3], v[4]]
Expect Intermediate: [v[1], v[2], v[3], v[4]]
Expect Intermediate: [v[1], v[2], v[3], v[4]]
Expect Intermediate: [v[1], v[2], v[3], v[4], v[5]]
Expect Intermediate: [v[1], v[2], v[3], v[4], v[5], v[6]]
Expect Final: [v[1], v[2], v[3], v[4], v[5], v[6]]
==>v[5]
==>v[5]
==>v[5]
Expect Final: [v[1], v[2], v[3], v[4], v[5], v[6]]
==>v[3]
==>v[3]
==>v[3]
gremlin> g.V().store("a").both().sideEffect(select("a").sideEffect {println
"Expect Intermediate: " + it.get()}).barrier().
......1> out().out().sideEffect(select("a").sideEffect {println "Expect
Final: " + it.get()}).explain()
==>Traversal Explanation
===========================================================================================================================================================================================================================================
Original Traversal [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
ConnectiveStrategy [D] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
MatchPredicateStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
InlineFilterStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
IncidentToAdjacentStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
AdjacentToIncidentStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
FilterRankingStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
RangeByIsCountStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
RepeatUnrollStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
PathRetractionStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
VertexStep(OUT,vertex)
,
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)])]
LazyBarrierStrategy [O] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
NoOpBarrierStep(2500),
VertexStep(OUT,vertex),
NoOpBarrierStep(2500), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)])]
TinkerGraphCountStrategy [P] [GraphStep(vertex,[]), StoreStep(a),
VertexStep(BOTH,vertex), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)]), NoOpBarrierStep, VertexStep(OUT,vertex),
NoOpBarrierStep(2500),
VertexStep(OUT,vertex),
NoOpBarrierStep(2500), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)])]
TinkerGraphStepStrategy [P] [TinkerGraphStep(vertex,[]),
StoreStep(a), VertexStep(BOTH,vertex),
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)]),
NoOpBarrierStep, VertexStep(OUT,vertex), NoOpBarrierStep(
2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)])]
ProfileStrategy [F] [TinkerGraphStep(vertex,[]),
StoreStep(a), VertexStep(BOTH,vertex),
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)]),
NoOpBarrierStep, VertexStep(OUT,vertex), NoOpBarrierStep(
2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)])]
StandardVerificationStrategy [V] [TinkerGraphStep(vertex,[]),
StoreStep(a), VertexStep(BOTH,vertex),
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)]),
NoOpBarrierStep, VertexStep(OUT,vertex), NoOpBarrierStep(
2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)])]
Final Traversal [TinkerGraphStep(vertex,[]),
StoreStep(a), VertexStep(BOTH,vertex),
TraversalSideEffectStep([SelectOneStep(a), LambdaSideEffectStep(lambda)]),
NoOpBarrierStep, VertexStep(OUT,vertex), NoOpBarrierStep(
2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), TraversalSideEffectStep([SelectOneStep(a),
LambdaSideEffectStep(lambda)])]
```
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