Occasional occurence of java.util.ConcurrentModificationException

[cerebis]

This is non-deterministic and appears to afflict any workflow I test. Given enough repeated tests, eventually you will get a ConcurrentModificationException, and this exception appears to occur at the same place each time. Namely, when Nextflow attempts to publish a collection of file outputs.

https://github.com/nextflow-io/nextflow/blob/master/src/main/groovy/nextflow/processor/TaskProcessor.groovy#L1197

Tests tried, which did not resolve the problem

• cache false
• publish overwrite false
• removal of a file from outputs which was previous published

Dec-01 16:18:50.848 [Thread-1] ERROR nextflow.processor.TaskProcessor - Error executing process > 'WGS_Reads (2)'

Caused by:
  java.util.ConcurrentModificationException

java.util.ConcurrentModificationException: null
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
	at java.util.ArrayList$Itr.next(ArrayList.java:851)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2029)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:1890)
	at nextflow.processor.TaskProcessor$_publishOutputs_closure24.doCall(TaskProcessor.groovy:1197)
	at sun.reflect.GeneratedMethodAccessor386.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
	at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:294)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1024)
	at groovy.lang.Closure.call(Closure.java:414)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.callClosureForMapEntry(DefaultGroovyMethods.java:5226)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.each(DefaultGroovyMethods.java:2107)
	at nextflow.processor.TaskProcessor.publishOutputs(TaskProcessor.groovy:1192)
	at sun.reflect.GeneratedMethodAccessor374.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:210)
	at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.callCurrent(PogoMetaMethodSite.java:59)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:166)
	at nextflow.processor.TaskProcessor.finalizeTask0(TaskProcessor.groovy:1973)
	at sun.reflect.GeneratedMethodAccessor367.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:210)
	at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.callCurrent(PogoMetaMethodSite.java:59)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:166)
	at nextflow.processor.TaskProcessor.finalizeTask(TaskProcessor.groovy:1944)
	at nextflow.processor.TaskPollingMonitor.checkTaskStatus(TaskPollingMonitor.groovy:438)
	at nextflow.processor.TaskPollingMonitor.checkAllTasks(TaskPollingMonitor.groovy:394)
	at nextflow.processor.TaskPollingMonitor.pollLoop(TaskPollingMonitor.groovy:340)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1215)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1024)
	at org.codehaus.groovy.runtime.InvokerHelper.invokePogoMethod(InvokerHelper.java:923)
	at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:906)
	at org.codehaus.groovy.runtime.InvokerHelper.invokeMethodSafe(InvokerHelper.java:74)
	at nextflow.processor.TaskPollingMonitor$_start_closure6.doCall(TaskPollingMonitor.groovy:319)
	at nextflow.processor.TaskPollingMonitor$_start_closure6.call(TaskPollingMonitor.groovy)
	at groovy.lang.Closure.run(Closure.java:495)
	at java.lang.Thread.run(Thread.java:745)