Github user GCHQResearcher1337 commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/876#discussion_r195046349
--- Diff:
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/branch/RepeatTest.java
---
@@ -386,5 +456,26 @@ public void
g_V_hasXname_markoX_repeatXoutE_inV_simplePathX_untilXhasXname_rippl
public Traversal<Vertex, Path>
get_g_V_hasXloop_name_loopX_repeatXinX_timesX5X_path_by_name() {
return
g.V().has("loops","name","loop").repeat(__.in()).times(5).path().by("name");
}
+
+ @Override
+ public Traversal<Vertex, Path>
get_g_V_repeatXout_repeatXoutX_timesX1XX_timesX1X_limitX1X_path_by_name() {
+ // NB We need to prevent the RepeatUnrollStrategy from
applying to properly exercise this test as this traversal can be simplified
--- End diff --
Thanks @spmallette I wanted to do something like this but hadn't spotted
these tests. While writing some tests I've noticed that when
RepeatUnrollStrategy is applied from the inside out, adding a barrier step onto
the end:
repeat(a.repeat(b).times(1)).times(1) -> repeat(a.b.barrier).times(1)
repeat(a.b.barrier).times(1) -> a.b.barrier.barrier
eg
```
gremlin> g.V().repeat(out().repeat(out()).times(1)).times(1).explain()
==>Traversal Explanation
===========================================================================================================================================================================================================================
Original Traversal [GraphStep(vertex,[]),
RepeatStep([VertexStep(OUT,vertex), RepeatStep([VertexStep(OUT,vertex),
RepeatEndStep],until(loops(1)),emit(false)),
RepeatEndStep],until(loops(1)),emit(false))]
ConnectiveStrategy [D] [GraphStep(vertex,[]),
RepeatStep([VertexStep(OUT,vertex), RepeatStep([VertexStep(OUT,vertex),
RepeatEndStep],until(loops(1)),emit(false)),
RepeatEndStep],until(loops(1)),emit(false))]
MatchPredicateStrategy [O] [GraphStep(vertex,[]),
RepeatStep([VertexStep(OUT,vertex), RepeatStep([VertexStep(OUT,vertex),
RepeatEndStep],until(loops(1)),emit(false)),
RepeatEndStep],until(loops(1)),emit(false))]
FilterRankingStrategy [O] [GraphStep(vertex,[]),
RepeatStep([VertexStep(OUT,vertex), RepeatStep([VertexStep(OUT,vertex),
RepeatEndStep],until(loops(1)),emit(false)),
RepeatEndStep],until(loops(1)),emit(false))]
InlineFilterStrategy [O] [GraphStep(vertex,[]),
RepeatStep([VertexStep(OUT,vertex), RepeatStep([VertexStep(OUT,vertex),
RepeatEndStep],until(loops(1)),emit(false)),
RepeatEndStep],until(loops(1)),emit(false))]
IncidentToAdjacentStrategy [O] [GraphStep(vertex,[]),
RepeatStep([VertexStep(OUT,vertex), RepeatStep([VertexStep(OUT,vertex),
RepeatEndStep],until(loops(1)),emit(false)),
RepeatEndStep],until(loops(1)),emit(false))]
AdjacentToIncidentStrategy [O] [GraphStep(vertex,[]),
RepeatStep([VertexStep(OUT,vertex), RepeatStep([VertexStep(OUT,vertex),
RepeatEndStep],until(loops(1)),emit(false)),
RepeatEndStep],until(loops(1)),emit(false))]
RepeatUnrollStrategy [O] [GraphStep(vertex,[]),
VertexStep(OUT,vertex), VertexStep(OUT,vertex), NoOpBarrierStep(2500),
NoOpBarrierStep(2500)]
CountStrategy [O] [GraphStep(vertex,[]),
VertexStep(OUT,vertex), VertexStep(OUT,vertex), NoOpBarrierStep(2500),
NoOpBarrierStep(2500)]
PathRetractionStrategy [O] [GraphStep(vertex,[]),
VertexStep(OUT,vertex), VertexStep(OUT,vertex), NoOpBarrierStep(2500),
NoOpBarrierStep(2500)]
LazyBarrierStrategy [O] [GraphStep(vertex,[]),
VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), NoOpBarrierStep(2500)]
TinkerGraphCountStrategy [P] [GraphStep(vertex,[]),
VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), NoOpBarrierStep(2500)]
TinkerGraphStepStrategy [P] [TinkerGraphStep(vertex,[]),
VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), NoOpBarrierStep(2500)]
ProfileStrategy [F] [TinkerGraphStep(vertex,[]),
VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), NoOpBarrierStep(2500)]
StandardVerificationStrategy [V] [TinkerGraphStep(vertex,[]),
VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), NoOpBarrierStep(2500)]
Final Traversal [TinkerGraphStep(vertex,[]),
VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex),
NoOpBarrierStep(2500), NoOpBarrierStep(2500)]
```
Do you think it's ok to leave multiple barrier steps at the end? I could
add an extra check that we aren't inserting a barrier after a barrier here -
but this could interfere with a barrier added by a user?
https://github.com/apache/tinkerpop/blob/d3b6a340dbb9c89355c40089a5c083dc0dbd4c5b/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/optimization/RepeatUnrollStrategy.java#L72
---
