[MNG-7716] ConcurrencyDependencyGraph deadlock if no root can be selected

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.8.7, 3.9.0, 4.0.0-alpha-4
• Fix Version/s: 3.8.8, 3.9.1, 4.0.0-alpha-5, 4.0.0
• Component/s: Core
• Assignee: Michael Osipov
• Reporter: Christoph Läubrich
• Created: 02/Mar/23 14:26
• Updated: 14/Mar/23 13:36
• Resolved: 03/Mar/23 17:08

Description

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

  org.faktorips:base:pom:23.6.0-SNAPSHOT -> [org.eclipse.tycho:tycho-versions-plugin:3.0.4-SNAPSHOT:set-version]

• This segment has a transitive reactor dependency to

  MavenProject: org.faktorips:codequality-config:23.6.0-SNAPSHOT @ faktorips.base/codequality-config/pom.xml

  (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

Issue Links

• links to: GitHub Pull Request #250
• links to: GitHub Pull Request #1027
• links to: GitHub Pull Request #1028
• links to: GitHub Pull Request #1029