[VELOCITY-934] NullPointerException under high concurrency

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Information Provided
• Affects Version/s: 1.7.x, 2.2
• Component/s: Engine
• Environment: Windows 10 Professional
• Assignee: Unassigned
• Reporter: Andreas Hager
• Created: 15/Nov/20 19:23
• Updated: 08/Dec/20 22:41
• Resolved: 08/Dec/20 22:41

Description

I adjusted the mboseke/template-benchmark to profile throughput on AMD Ryzen 5950x:

https://github.com/casid/template-benchmark/tree/ryzen-5950x

With 32 concurrent threads, I can reliably reproduce a runtime exception in the Apache Velocity benchmark:

java.lang.NullPointerException
        at org.apache.velocity.runtime.directive.Directive.postRender(Directive.java:240)
        at org.apache.velocity.runtime.directive.Foreach.clean(Foreach.java:325)
        at org.apache.velocity.runtime.directive.Foreach.render(Foreach.java:292)
        at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:301)
        at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:423)
        at org.apache.velocity.Template.merge(Template.java:358)
        at org.apache.velocity.Template.merge(Template.java:262)
        at com.mitchellbosecke.benchmark.Velocity.benchmark(Velocity.java:34)
        at com.mitchellbosecke.benchmark.generated.Velocity_benchmark_jmhTest.benchmark_thrpt_jmhStub(Velocity_benchmark_jmhTest.java:122)
        at com.mitchellbosecke.benchmark.generated.Velocity_benchmark_jmhTest.benchmark_Throughput(Velocity_benchmark_jmhTest.java:69)
        at jdk.internal.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.openjdk.jmh.runner.BenchmarkHandler$BenchmarkTask.call(BenchmarkHandler.java:430)
        at org.openjdk.jmh.runner.BenchmarkHandler$BenchmarkTask.call(BenchmarkHandler.java:412)
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at java.base/java.lang.Thread.run(Thread.java:834)

This initially happened with version 1.7, but after updating to 2.2 the problem is still there. It looks like there is some threading issue under high concurrency.

This is the velocity benchmark class:

https://github.com/casid/template-benchmark/blob/ryzen-5950x/src/main/java/com/mitchellbosecke/benchmark/Velocity.java

And this is the velocity template:

https://github.com/casid/template-benchmark/blob/ryzen-5950x/src/main/resources/templates/stocks.velocity.html