Another race condition in PipelineMainTest

[retronym]

Jenkins CI failed of a commit in scala/scala#9276

Hung with:

"pool-1-thread-1" #11 prio=5 os_prio=0 tid=0x00007f17182e3800 nid=0x5bd1 runnable [0x00007f16ea9f0000]
   java.lang.Thread.State: RUNNABLE
	at scala.runtime.BoxesRunTime.equals2(BoxesRunTime.java:137)
	at scala.runtime.BoxesRunTime.equals(BoxesRunTime.java:123)
	at scala.collection.mutable.HashTable.elemEquals(HashTable.scala:365)
	at scala.collection.mutable.HashTable.elemEquals$(HashTable.scala:365)
	at scala.collection.mutable.LinkedHashSet.elemEquals(LinkedHashSet.scala:44)
	at scala.collection.mutable.HashTable.findEntry0(HashTable.scala:140)
	at scala.collection.mutable.HashTable.findOrAddEntry(HashTable.scala:169)
	at scala.collection.mutable.HashTable.findOrAddEntry$(HashTable.scala:167)
	at scala.collection.mutable.LinkedHashSet.findOrAddEntry(LinkedHashSet.scala:44)
	at scala.collection.mutable.LinkedHashSet.add(LinkedHashSet.scala:68)
	at scala.collection.mutable.LinkedHashSet.$plus$eq(LinkedHashSet.scala:63)
	at scala.tools.nsc.reporters.StoreReporter.doReport(StoreReporter.scala:35)
	at scala.tools.nsc.reporters.FilteringReporter.info0(Reporter.scala:92)
	at scala.reflect.internal.Reporter.echo(Reporting.scala:109)
	at scala.reflect.internal.Reporter.echo(Reporting.scala:108)
	at scala.tools.nsc.PipelineMainClass.writeDotFile(PipelineMain.scala:92)
	at scala.tools.nsc.PipelineMainClass.$anonfun$process$78(PipelineMain.scala:297)
	at scala.tools.nsc.PipelineMainClass.process(PipelineMain.scala:295)
	at scala.tools.nsc.PipelineMainTest.$anonfun$check$1(PipelineMainTest.scala:62)
	at scala.tools.nsc.PipelineMainTest.build$1(PipelineMainTest.scala:59)
	at scala.tools.nsc.PipelineMainTest.check(PipelineMainTest.scala:65)
	at scala.tools.nsc.PipelineMainTest.pipelineMainBuildsCombined(PipelineMainTest.scala:38)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runners.Suite.runChild(Suite.java:128)
	at org.junit.runners.Suite.runChild(Suite.java:27)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:115)
	at com.novocode.junit.JUnitRunner$1.execute(JUnitRunner.java:132)
	at sbt.ForkMain$Run.lambda$runTest$1(ForkMain.java:304)
	at sbt.ForkMain$Run$$Lambda$5/1394438858.call(Unknown Source)

Which is possibly due to multi-threaded use of StoreReporter which has an thread-unsafe collection inside it.

[dwijnand]

Hasn't been spotted in recent times. Hopefully gone for good. We'll reopen if necessary.

[retronym]

I've submitted a fix for this, Murphy's law suggest that the race will come back at the worst possible time like during a release build.

scala/scala#9455