Description

Every so often we see a CME due to the underlying implementation of List being used is ArrayList.

11:25:37  java.util.ConcurrentModificationException
11:25:37  	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
11:25:37  	at java.util.ArrayList$Itr.next(ArrayList.java:859)
11:25:37  	at hudson.plugins.s3.S3Profile.downloadAll(S3Profile.java:240)
11:25:37  	at hudson.plugins.s3.S3CopyArtifact.perform(S3CopyArtifact.java:270)
11:25:37  	at hudson.plugins.s3.S3CopyArtifact.perform(S3CopyArtifact.java:242)
11:25:37  	at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:80)

• Modifying the implementation so that a thread-safe variant of the List is used in place.
• I used a CopyOnWriteArrayList and that should prevent the CME from being thrown. Ideally an alternative Concurrent collection or synchronization around the original ArrayList would be done. However, this seems to be the least intrusive way of getting around the exception being thrown.

Testing

• Tested this change locally on our own Jenkins instance and things were running fine.
• The CI running within Github is somehow not happy about the versions of dependencies being used and seems to be an error not directly related to my change.