Background

New class called PlotBuildAction was added when compatibility with Pipeline plugin was implemented in https://github.com/jenkinsci/plot-plugin/pull/32.
Seems like this class current implementation is not thread safe and user reported 1st time issue with ConcurrentModificationException in PR comment. Exception was not reproducible to me even though I used provided by reporter Jenkins & Pipeline configurations.
There was an attempt to blindly fix the issue in commit, but it didn't work out.
Second report about the same exception appeared recently.

svanoort proposed copy-on-write approach rather than synchronized for methods. It should be considered as potential fix.

Environment

• Plot plugin version is 1.2.0.
• Environment.

What should be done

• We need to reproduce ConcurrentModificationException while accessing plots array in PlotBuildAction and fix it.
• It's good to have a test for the fix

How to test

• If issue is reproducible, test should be written
• Gather feedback from https://github.com/dolfinsbizou and https://github.com/shawnhines as they reported about this exception and can verify on their environments