Jenkins pipeline scripted parallels

/* Example from "alcohol" on Jenkins IRC 2019-07-02
 * Also mentioned https://devops.stackexchange.com/questions/986/how-to-build-a-complex-parallel-jenkins-pipeline
 */

      stage('update playgrounds') {
        String[] playgrounds = sh(
          script: "kubectl get namespace --selector playground/frontend=${branch} --output jsonpath='{.items[*].metadata.name}'",
          returnStdout: true
        ).trim().split()

        Map mapped = playgrounds.collectEntries { String namespace ->
          ["${namespace}": {
            stage ("update ${namespace}") {
              sh """
                bunch of commands to update a playground
                """.stripIndent()

              playgroundUpdated(namespace.replaceAll('playground-', ''), env.BRANCH_NAME, commit)
            }
          }]
        }

        mapped['failFast'] = true;

        parallel mapped
      }