Using Maven 3.5.2, and the project compiler plugin configured as stated here the maven build output will report the following. Note that this is only a warning as far as I can tell with no impact to the build.

I invoked maven specifically to be multi-threaded via: "mvn clean install -T 1C"

[WARNING] *****************************************************************
[WARNING] * Your build is requesting parallel execution, but project *
[WARNING] * contains the following plugin(s) that have goals not marked *
[WARNING] * as @threadsafe to support parallel building. *
[WARNING] * While this /may/ work fine, please look for plugin updates *
[WARNING] * and/or request plugins be made thread-safe. *
[WARNING] * If reporting an issue, report it against the plugin in *
[WARNING] * question, not against maven-core *
[WARNING] *****************************************************************
[WARNING] The following plugins are not marked @threadsafe in Data Source Common WS:
[WARNING] org.codehaus.groovy:groovy-eclipse-compiler:2.9.2-04
[WARNING] Enable debug to see more precisely which goals are not marked @threadsafe.
[WARNING] *****************************************************************

I suggest that if appropriate, the @threadsafe annotation should be added to compiler source code so that the Maven warning no longer displays.