TINKERPOP-3210 Fix cap() step mid-traversal in OLAP

Added check to memory.set() to ensure masterState() in MemoryTraversalSideEffects. Changed TraversalVertexProgram to gather all completed barriers across all rounds which prevented stale lazy re-evaluation.

Author: spmallette

CHANGELOG.asciidoc

@@ -35,6 +35,7 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 * Added `SessionedChildClient` that borrows connections from a different `Client` for use with `Sessions`.
 * Added `reuseConnectionsForSessions` to Java GLV settings to decide whether to use `SessionedChildClient` for remote transactions.
 * Added support for Node 22 and 24 alongside Node 20.
+* Fixed `cap()` step throwing an error when used mid-traversal in OLAP.
 
 [[release-3-7-5]]
 === TinkerPop 3.7.5 (Release Date: November 12, 2025)

gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/traversal/MemoryTraversalSideEffects.java

@@ -57,7 +57,12 @@ public TraversalSideEffects getSideEffects() {
     @Override
     public void set(final String key, final Object value) {
         this.sideEffects.set(key, value);
-        if (null != this.memory)
+
+        // looks like calls to this method are only permitted during setup/terminate (i.e. masterState)
+        // during worker execution (e.g. cap() firing lazily via a downstream local step), skip the
+        // memory write to avoid IllegalArgumentException from the distributed memory implementation.
+        // see TINKERPOP-3210 for an example of how this fails.
+        if (null != this.memory && this.phase.masterState())
             this.memory.set(key, value);
     }
 

gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/traversal/TraversalVertexProgram.java

@@ -329,8 +329,13 @@ public boolean terminate(final Memory memory) {
             MasterExecutor.processMemory(this.traversalMatrix, memory, toProcessTraversers, completedBarriers);
             // process all results from barriers locally and when elements are touched, put them in remoteActiveTraversers
             MasterExecutor.processTraversers(this.traversal, this.traversalMatrix, toProcessTraversers, remoteActiveTraversers, haltedTraversers, this.haltedTraverserStrategy);
-            // tell parallel barriers that might not have been active in the last round that they are no longer active
-            memory.set(COMPLETED_BARRIERS, completedBarriers);
+            // tell parallel barriers that might not have been active in the last round that they are no longer active.
+            // accumulate all previously-completed barriers: worker clones start with done=false and need done() called
+            // for every barrier ever completed (not just the most recent ones) to prevent stale lazy re-evaluation.
+            // see TINKERPOP-3210 for the lazy cap() re-firing that motivated this change.
+            final Set<String> allCompletedBarriers = new HashSet<>(memory.get(COMPLETED_BARRIERS));
+            allCompletedBarriers.addAll(completedBarriers);
+            memory.set(COMPLETED_BARRIERS, allCompletedBarriers);
             if (!remoteActiveTraversers.isEmpty() ||
                     completedBarriers.stream().map(this.traversalMatrix::getStepById).filter(step -> step instanceof LocalBarrier).findAny().isPresent()) {
                 // send active traversers back to workers

gremlin-dotnet/test/Gremlin.Net.IntegrationTest/Gherkin/Gremlin.cs

@@ -1483,6 +1483,9 @@ private static IDictionary<string, List<Func<GraphTraversalSource, IDictionary<s
                {"g_withSideEffectXa_xx1_addAllX_V_aggregateXlocal_aX_byXageX_capXaX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.WithSideEffect("a",p["xx1"],Operator.AddAll).V().Aggregate(Scope.Local,"a").By("age").Cap<object>("a")}}, 
                {"g_withSideEffectXa_xx1_assignX_V_aggregateXaX_byXageX_capXaX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.WithSideEffect("a",p["xx1"],Operator.Assign).V().Aggregate("a").By("age").Cap<object>("a")}}, 
                {"g_withSideEffectXa_xx1_assignX_V_order_byXageX_aggregateXlocal_aX_byXageX_capXaX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.WithSideEffect("a",p["xx1"],Operator.Assign).V().Order().By("age").Aggregate(Scope.Local,"a").By("age").Cap<object>("a")}}, 
+               {"g_V_repeatXaggregateXaXX_timesX2X_capXaX_unfold", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Repeat(__.Aggregate("a")).Times(2).Cap<object>("a").Unfold<object>()}}, 
+               {"g_V_aggregateXaX_capXaX_unfold_both", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Aggregate("a").Cap<object>("a").Unfold<object>().Both()}}, 
+               {"g_V_aggregateXaX_capXaX_unfold_barrier_both", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Aggregate("a").Cap<object>("a").Unfold<object>().Barrier().Both()}}, 
                {"g_V_fail", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Fail()}}, 
                {"g_V_failXmsgX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Fail("msg")}}, 
                {"g_V_unionXout_failX", new List<Func<GraphTraversalSource, IDictionary<string, object>, ITraversal>> {(g,p) =>g.V().Union<object>(__.Out(),__.Fail())}}, 

gremlin-go/driver/cucumber/gremlin.go

@@ -1454,6 +1454,9 @@ var translationMap = map[string][]func(g *gremlingo.GraphTraversalSource, p map[
     "g_withSideEffectXa_xx1_addAllX_V_aggregateXlocal_aX_byXageX_capXaX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.WithSideEffect("a", p["xx1"], gremlingo.Operator.AddAll).V().Aggregate(gremlingo.Scope.Local, "a").By("age").Cap("a")}}, 
     "g_withSideEffectXa_xx1_assignX_V_aggregateXaX_byXageX_capXaX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.WithSideEffect("a", p["xx1"], gremlingo.Operator.Assign).V().Aggregate("a").By("age").Cap("a")}}, 
     "g_withSideEffectXa_xx1_assignX_V_order_byXageX_aggregateXlocal_aX_byXageX_capXaX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.WithSideEffect("a", p["xx1"], gremlingo.Operator.Assign).V().Order().By("age").Aggregate(gremlingo.Scope.Local, "a").By("age").Cap("a")}}, 
+    "g_V_repeatXaggregateXaXX_timesX2X_capXaX_unfold": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Repeat(gremlingo.T__.Aggregate("a")).Times(2).Cap("a").Unfold()}}, 
+    "g_V_aggregateXaX_capXaX_unfold_both": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Aggregate("a").Cap("a").Unfold().Both()}}, 
+    "g_V_aggregateXaX_capXaX_unfold_barrier_both": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Aggregate("a").Cap("a").Unfold().Barrier().Both()}}, 
     "g_V_fail": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Fail()}}, 
     "g_V_failXmsgX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Fail("msg")}}, 
     "g_V_unionXout_failX": {func(g *gremlingo.GraphTraversalSource, p map[string]interface{}) *gremlingo.GraphTraversal {return g.V().Union(gremlingo.T__.Out(), gremlingo.T__.Fail())}}, 

gremlin-javascript/src/main/javascript/gremlin-javascript/test/cucumber/gremlin.js

@@ -1456,6 +1456,8 @@
     'g_withSideEffectXa_xx1_addAllX_V_aggregateXlocal_aX_byXageX_capXaX': [(lambda g, xx1=None:g.with_side_effect('a',xx1,Operator.add_all).V().aggregate(Scope.local,'a').by('age').cap('a'))], 
     'g_withSideEffectXa_xx1_assignX_V_aggregateXaX_byXageX_capXaX': [(lambda g, xx1=None:g.with_side_effect('a',xx1,Operator.assign).V().aggregate('a').by('age').cap('a'))], 
     'g_withSideEffectXa_xx1_assignX_V_order_byXageX_aggregateXlocal_aX_byXageX_capXaX': [(lambda g, xx1=None:g.with_side_effect('a',xx1,Operator.assign).V().order().by('age').aggregate(Scope.local,'a').by('age').cap('a'))], 
+    'g_V_aggregateXaX_capXaX_unfold_both': [(lambda g:g.V().aggregate('a').cap('a').unfold().both())], 
+    'g_V_aggregateXaX_capXaX_unfold_barrier_both': [(lambda g:g.V().aggregate('a').cap('a').unfold().barrier().both())], 
     'g_V_fail': [(lambda g:g.V().fail())], 
     'g_V_failXmsgX': [(lambda g:g.V().fail('msg'))], 
     'g_V_unionXout_failX': [(lambda g:g.V().union(__.out(),__.fail()))], 

gremlin-python/src/main/python/tests/feature/gremlin.py

@@ -576,3 +576,69 @@ Feature: Step - aggregate()
     Then the result should be unordered
       | result |
       | d[35].i |
+
+  Scenario: g_V_repeatXaggregateXaXX_timesX2X_capXaX_unfold
+    Given the modern graph
+    And the traversal of
+      """
+      g.V().repeat(__.aggregate("a")).times(2).cap("a").unfold()
+      """
+    When iterated to list
+    Then the result should be unordered
+      | result |
+      | v[marko] |
+      | v[marko] |
+      | v[vadas] |
+      | v[vadas] |
+      | v[lop] |
+      | v[lop] |
+      | v[josh] |
+      | v[josh] |
+      | v[ripple] |
+      | v[ripple] |
+      | v[peter] |
+      | v[peter] |
+
+  Scenario: g_V_aggregateXaX_capXaX_unfold_both
+    Given the modern graph
+    And the traversal of
+      """
+      g.V().aggregate("a").cap("a").unfold().both()
+      """
+    When iterated to list
+    Then the result should be unordered
+      | result |
+      | v[marko] |
+      | v[marko] |
+      | v[marko] |
+      | v[vadas] |
+      | v[josh] |
+      | v[josh] |
+      | v[josh] |
+      | v[lop] |
+      | v[lop] |
+      | v[lop] |
+      | v[peter] |
+      | v[ripple] |
+
+  Scenario: g_V_aggregateXaX_capXaX_unfold_barrier_both
+    Given the modern graph
+    And the traversal of
+      """
+      g.V().aggregate("a").cap("a").unfold().barrier().both()
+      """
+    When iterated to list
+    Then the result should be unordered
+      | result |
+      | v[marko] |
+      | v[marko] |
+      | v[marko] |
+      | v[vadas] |
+      | v[josh] |
+      | v[josh] |
+      | v[josh] |
+      | v[lop] |
+      | v[lop] |
+      | v[lop] |
+      | v[peter] |
+      | v[ripple] |