Throttle parallel step in Jenkins pipeline script

Question

I'm using something like this to run tests in parallel:

stage('Test') {
  steps {
    script {
      testing_closures = [one: { print("staring one"); sleep 10; print("finishing one") },
                          two: { print("staring two"); sleep 10; print("finishing two") },
                          three: { print("staring three"); sleep 10; print("finishing three") },
                          four: { print("staring four"); sleep 10; print("finishing four") },
                          five: { print("staring five"); sleep 10; print("finishing five") },
                          six: { print("staring six"); sleep 10; print("finishing six") }]
      parallel(testing_closures)
    }
  }
}

The main goal is to throttle those closures - I don't want for all six of them to run concurrently - only 3 at a time. And I want to be able to run another build of this, which will also run all of those closures, but only 3 simultaneously.

I was thinking about using nodes for this - i.e. wrapping each closure in node{} block:

one: { node { print("staring one"); sleep 10; print("finishing one") } }

Works OK as long as I use master node and limit the executors to 4 (1 for main job, 3 for the node{} concurrent steps).

Unfortunately I need master node executors to be available for other jobs (and other builds of the job in question), so I cannot limit them.

The only solution I could think of is to use Lockable Resources in following manner:

1. Dynamically create 3 lockable resources via LockableResourcesManager::createResourceWithLabel() with build-unique labels

2. Lock them by label in all of the closures

3. The closures will wait for each other to finish and only 3 at the time would be running.

4. ...and now I'm stuck. I could not find any method to delete the resources. I only found an open bug for quite similar issue. EDIT: I created improvement request for it.

Even if there is a method to delete the resources, this solution looks dirty and adds unnecessary resources that may not clean up if something fails.

So - how do I achieve my goal? Is there a way to throttle parallel step?

Answer 1

You could definitely do that with LockableResources Plugin, just define 3 resources for a given label, and use the quantity needed for each critical step to be 1. (otherwise it would require all the resources from the labels given)

node('slave') {
    def execs = [:]
    execs[1] = {
        lock(label: 'Win81x64Pool', quantity: 1, variable: "MY_VAR") {
            println "LOCKED=" + env.MY_VAR
            sleep(3)
       }
    }
    execs[2] = {
        lock(label: 'Win81x64Pool', quantity: 1, variable: "MY_VAR") {
            println "LOCKED=" + env.MY_VAR
            sleep(3)
        }
    }
    execs[3] = {
        lock(label: 'Win81x64Pool', quantity: 1, variable: "YOUR_VAR") {
            println "LOCKED=" + env.YOUR_VAR
            sleep(3)
        }
    }
    parallel execs
}