[BEAM-12215] DirectRunner NullPointerException

• Type: Bug
• Status: Triage Needed
• Priority: P3
• Resolution: Unresolved
• Affects Version/s: 2.28.0
• Component/s: runner-direct, sdk-java-core, testing
• Assignee: Unassigned
• Reporter: Lai Jiang
• Created: 23/Apr/21 13:42
• Updated: 04/Jun/22 19:58

Description

When using the DirectRunner in tests I encountered flaky tests due to NullPointerException.

When the test fails the relevant stack trace is like below:

 

 

java.lang.NullPointerException
 at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkNotNull(Preconditions.java:877)
 at org.apache.beam.vendor.guava.v26_0_jre.com.google.common.util.concurrent.ThreadFactoryBuilder.setThreadFactory(ThreadFactoryBuilder.java:132)
 at org.apache.beam.runners.direct.DirectRunner.run(DirectRunner.java:192)
 at org.apache.beam.runners.direct.DirectRunner.run(DirectRunner.java:67)
 at org.apache.beam.sdk.Pipeline.run(Pipeline.java:322)
 at google.registry.beam.TestPipelineExtension.run(TestPipelineExtension.java:344)
 at google.registry.beam.TestPipelineExtension.run(TestPipelineExtension.java:324)
 at google.registry.beam.spec11.Spec11PipelineTest.testSuccess_saveToGcs(Spec11PipelineTest.java:185)

 

 
However the null pointer seems to have come from calling (a repackaged and very innocent looking) guava function to set the ThreadFactory:
 

 ExecutorService metricsPool =
 Executors.newCachedThreadPool(
 new ThreadFactoryBuilder()
.setThreadFactory(MoreExecutors.platformThreadFactory())
 .setDaemon(false) // otherwise you say you want to leak, please don't!
 .setNameFormat("direct-metrics-counter-committer")
 .build());

 
Which in turn is just calling java.util.concurrent.Executors.defaulThreatFactory() when not on App Engine:
 

@Beta
@GwtIncompatible
public static ThreadFactory platformThreadFactory() {
 if (!isAppEngine()) {
  return Executors.defaultThreadFactory();
  } else {
 ...
} 

 

I don't understand how this could possibly have failed. The test seems to be only flaky on our CI servers running Ubuntu and I haven't been able to reproduce it locally, making debugging a challenge.

 

I'd appreciate any input you may have. Thanks!