[jira] [Created] (MNG-7716) ConcurrencyDependencyGraph deadlock if no root can be selected

["Christoph Läubrich (Jira)" <ji...@apache.org>]

Christoph Läubrich created MNG-7716:
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             Summary: ConcurrencyDependencyGraph deadlock if no root can be selected
                 Key: MNG-7716
                 URL: https://issues.apache.org/jira/browse/MNG-7716
             Project: Maven
          Issue Type: Bug
            Reporter: Christoph Läubrich


At Tycho we got a bug-report that results in a deadlock when calling the tycho-version-plugin:
https://github.com/eclipse-tycho/tycho/issues/2169

I debugged the problem and it seems that ConcurrencyDependencyGraph is actually the culprit here because it can return an empty list of projects to initially build. As no builds are scheduled then the code in the MultiThreadedBuilder waits forever for the result, this is what happening here:

* There is one segment {code}org.faktorips:base:pom:23.6.0-SNAPSHOT -> [org.eclipse.tycho:tycho-versions-plugin:3.0.4-SNAPSHOT:set-version]{code}
* This segment has a transitive reactor dependency to {code}MavenProject: org.faktorips:codequality-config:23.6.0-SNAPSHOT @ faktorips.base/codequality-config/pom.xml{code} (this is not a problem because we only execute a reactor=true mojo!)
* So now the loop finds that there is no "independent" project and returns an empty list



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