The git extension h.p.g.e.PreBuildMerge Merge before build is using master workspace to try merging git branches.

But if executed concurrently this can cause concurrent access to git lock file stderr: fatal: Unable to create '/var/jenkins_home/workspace/pipeline-foo@script/.git/index.lock': File exists.

Quick look at it maybe possible options/ideas:

• mark the extension requiresWorkspaceForPolling

• override change method getWorkingDirectory to return a new directory if context.isConcurrentBuild()

• override decorateCheckoutCommand to use different directory