def build_if_needed(project) {
  println "build_if_needed: $project"
  // ultimately this will kick off a build job...
}

parallel (
  aaa : { build_if_needed('aaa')},
  bbb : { build_if_needed('bbb')},
  ccc : { build_if_needed('ccc')},
  ddd : { build_if_needed('ddd')},
  eee : { build_if_needed('eee')}
)

[Pipeline] parallel
[Pipeline] [aaa] { (Branch: aaa)
[Pipeline] [bbb] { (Branch: bbb)
[Pipeline] [ccc] { (Branch: ccc)
[Pipeline] [ddd] { (Branch: ddd)
[Pipeline] [eee] { (Branch: eee)
[Pipeline] [aaa] echo
[aaa] build_if_needed: eee
[Pipeline] [aaa] }
[Pipeline] [bbb] echo
[bbb] build_if_needed: eee
[Pipeline] [bbb] }
[Pipeline] [ccc] echo
[ccc] build_if_needed: eee
[Pipeline] [ccc] }
[Pipeline] [ddd] echo
[ddd] build_if_needed: eee
[Pipeline] [ddd] }
[Pipeline] [eee] echo
[eee] build_if_needed: eee
[Pipeline] [eee] }
[Pipeline] // parallel
[Pipeline] End of Pipeline
Finished: SUCCESS