`ConcurrentModificationException` running `add-third-party` goal

[Stephan202]

Today I observed the following build failure, after many successful executions of the add-third-party goal in various large (concurrent) Maven builds:

[ERROR] Failed to execute goal org.codehaus.mojo:license-maven-plugin:2.0.0:add-third-party (check-third-party-licenses) on project some-internal-project: could not init goal AddThirdPartyMojo for reason : null: ConcurrentModificationException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.mojo:license-maven-plugin:2.0.0:add-third-party (check-third-party-licenses) on project some-internal-project: could not init goal AddThirdPartyMojo for reason : null
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
    at java.util.concurrent.FutureTask.run (FutureTask.java:264)
    at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:515)
    at java.util.concurrent.FutureTask.run (FutureTask.java:264)
    at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1128)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:628)
    at java.lang.Thread.run (Thread.java:834)
Caused by: org.apache.maven.plugin.MojoExecutionException: could not init goal AddThirdPartyMojo for reason : null
    at org.codehaus.mojo.license.AbstractLicenseMojo.execute (AbstractLicenseMojo.java:185)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
    at java.util.concurrent.FutureTask.run (FutureTask.java:264)
    at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:515)
    at java.util.concurrent.FutureTask.run (FutureTask.java:264)
    at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1128)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:628)
    at java.lang.Thread.run (Thread.java:834)
Caused by: java.util.ConcurrentModificationException
    at java.util.TreeMap$PrivateEntryIterator.nextEntry (TreeMap.java:1208)
    at java.util.TreeMap$EntryIterator.next (TreeMap.java:1244)
    at java.util.TreeMap$EntryIterator.next (TreeMap.java:1239)
    at java.util.TreeMap.buildFromSorted (TreeMap.java:2554)
    at java.util.TreeMap.buildFromSorted (TreeMap.java:2578)
    at java.util.TreeMap.buildFromSorted (TreeMap.java:2546)
    at java.util.TreeMap.buildFromSorted (TreeMap.java:2578)
    at java.util.TreeMap.buildFromSorted (TreeMap.java:2546)
    at java.util.TreeMap.buildFromSorted (TreeMap.java:2503)
    at java.util.TreeMap.putAll (TreeMap.java:318)
    at org.codehaus.mojo.license.api.DependenciesTool.loadProjectDependencies (DependenciesTool.java:120)
    at org.codehaus.mojo.license.api.DefaultThirdPartyHelper.loadDependencies (DefaultThirdPartyHelper.java:152)
    at org.codehaus.mojo.license.AddThirdPartyMojo.loadDependencies (AddThirdPartyMojo.java:226)
    at org.codehaus.mojo.license.AbstractAddThirdPartyMojo.init (AbstractAddThirdPartyMojo.java:750)
    at org.codehaus.mojo.license.AbstractLicenseMojo.execute (AbstractLicenseMojo.java:171)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:190)
    at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call (MultiThreadedBuilder.java:186)
    at java.util.concurrent.FutureTask.run (FutureTask.java:264)
    at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:515)
    at java.util.concurrent.FutureTask.run (FutureTask.java:264)
    at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1128)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:628)
    at java.lang.Thread.run (Thread.java:834)

The issue is that DefaultThirdPartyHelper#artifactCache is shared between (and updated by) multiple threads without sufficient synchronization. I'll open a PR with a suggested fix.

[bjanczak]

What is a status of that issue. We have experienced similar one.

[Stephan202]

@bjanczak there's a PR for this issue (#355), but this plugin does not appear to be actively maintained :disappointed: . We're also still hitting this issue frequently.

Can one of the maintainers please have a look at this :point_up: PR? It's a very tiny fix.