Lazy initialization of recommendation providers is not thread-safe for multiproject builds with --parallel

[cbue]

Hi!

The recommendation plugin traverses up the project hierarchy to find a suitable recommendation in one of the parent projects, which is a good feature.

But as soon as the "--parallel" switch comes into play, a common parant project recommendation container gets requested by multiple threads in parallel.

My builds fail because a not completely preinitialized recommendation-HashMap is returned by the MavenBomRecommendationProvider in those situations.

Currenly we only use the MavenBomRecommendationProvider but by reviewing the code I found the same issue in:

• MavenBomRecommendationProvider
• DependencyLockProvider.groovy
• IvyRecommendationProvider.groovy
• PropertyFileRecommendationProvider.java

I will prepare two pull requests with fixes. One for the MavenBomRecommendationProvider which I tested successfully in my project and another one for the other three fixes.

Could you please review my code changes and merge the changes if suitable?

Thanks!

Regards
Christian