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https://issues.apache.org/jira/browse/TINKERPOP-967?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16543605#comment-16543605
]
ASF GitHub Bot commented on TINKERPOP-967:
------------------------------------------
Github user GCHQResearcher1337 commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/876#discussion_r202445268
--- Diff:
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/traverser/B_LP_NL_O_P_S_SE_SL_Traverser.java
---
@@ -0,0 +1,156 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.tinkerpop.gremlin.process.traversal.traverser;
+
+import org.apache.commons.collections.map.ReferenceMap;
+import org.apache.tinkerpop.gremlin.process.traversal.Step;
+import
org.apache.tinkerpop.gremlin.process.traversal.traverser.util.LabelledCounter;
+
+
+import java.util.Iterator;
+import java.util.Stack;
+
+public class B_LP_NL_O_P_S_SE_SL_Traverser<T> extends
B_LP_O_P_S_SE_SL_Traverser<T> {
+
+ protected Stack<LabelledCounter> nestedLoops;
+ protected ReferenceMap loopNames = null;
--- End diff --
Yep :) magic. I think at garbage collection the entry will get removed, or
there will be on access checks of the validity of the reference. I've used
something similar before (can't quite remember what) but didn't want to
introduce an extra dependency, but luckily I found ReferenceMap in
org.apache.commons.collections which was already included and seems to do this.
I wasn't quite sure if these references would be safe to 'attaching' as I
don't fully understand this, but I think attaching only moves a traverser to a
different part of the graph so the References/counters should still be safe.
https://github.com/apache/tinkerpop/blob/a80eb84169048ed74c5ad27ebc4d12944fd0136a/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/util/Attachable.java#L62
> Support nested-repeat() structures
> ----------------------------------
>
> Key: TINKERPOP-967
> URL: https://issues.apache.org/jira/browse/TINKERPOP-967
> Project: TinkerPop
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.1.0-incubating
> Reporter: Marko A. Rodriguez
> Assignee: Marko A. Rodriguez
> Priority: Major
>
> All the internal plumbing is staged for this to happen, we just haven't gone
> all the way. In short, a {{NESTED_LOOP}} traverser has an internal
> {{loopStack}} where {{repeat(repeat())}} will have a {{loopStack}} of two.
> The {{it.loops()}} checks of the internal repeat will always check the top of
> the stack and when its done repeating will delete its counter off the top of
> the stack.
> [~dkuppitz]'s work on {{LoopStep}} will be backwards compatible. In
> {{RepeatStep}} we will support:
> {code}
> repeat('a',out('knows').repeat('b',out('parent')))
> {code}
> and thus, things like {{loops('a')}} as well as {{times('a',2)}}. Note that
> naming the loop stack will be a super rare case as most people will just
> assume standard nested looping semantics with a push/pop stack.
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