[TINKERPOP-2554] Extracting step metrics from ProfileStep throws NPE if the step was not triggered

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.4.10
• Fix Version/s: 3.4.12, 3.5.1, 3.6.0
• Component/s: process
• Assignee: Stephen Mallette
• Reporter: Saikiran Boga
• Created: 28/Apr/21 01:01
• Updated: 02/Jul/21 15:47
• Resolved: 02/Jul/21 15:47

Description

When extracting step metrics from ProfileStep, this code block below[1] assumes that step metrics is always initialized. But if a step does not invoke starts hasNext() or next() methods for any particular reason, this throws an NPE.

An example case where this could happen is if a step decides not to invoke any upstream step by halting the execution:

step1 -> ProfileStep -> step2 -> ProfileStep -> step3 -> ProfileStep -> step4 -> ProfileStep

In this case if say step3/4 decides not to get starts from previous step, then the step metrics on all the preceding ProfileStep are left uninitialized.

Sample trace:

java.lang.NullPointerException: null
at org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversalMetrics.addTopLevelMetrics(DefaultTraversalMetrics.java:157)
at org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversalMetrics.setMetrics(DefaultTraversalMetrics.java:143)
at org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.ProfileSideEffectStep.hasNext(ProfileSideEffectStep.java:75) 
at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.hasNext(ExpandableStepIterator.java:42)
...

[1] https://github.com/apache/tinkerpop/blob/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/util/DefaultTraversalMetrics.java#L157