How can I run each iteration of a for loop parallel in Jenkins pipeline?

Question

I have a pipeline job which run some sequence of action (Eg; Build >> Run >> Report). I ahave put this sequence in a for loop as I can get a parameter how many times I should repeat the same sequence. Please find the sample code I have written.

for (int i = 0; i < <param_val>; ++i){
    node{
        stage('Build') {
            build 'Build'
        }
        stage('Run') {
           build 'Run'
        }
        stage('Reporting') {
           build 'Reporting'
        }
    }
}

Now my code is waiting for one complete sequence to happen and then continue to run the next sequence. That is time consuming. I have more slave agents and can run the sequence in parallel. How can I run each iteration of a for loop parallel?

I have thought of a solution : have a pipeline having the actual sequence

node{
        stage('Build') {
            build 'Build'
        }
        stage('Run') {
           build 'Run'
        }
        stage('Reporting') {
           build 'Reporting'
        }
    }

have another pipeline with the for loop which will trigger the 1st pipeline with wait: false:

for (int i = 0; i < <param_val>; ++i){
    build(job: 'pipeline-1', wait: false)
}

Does this work ? Or do we have a better option to do the same with single pipeline ?

Answer 1

Put the code inside the loop in a closure:

def oneNode = { c ->
    node {
        build job: 'Build', parameters: [string(name: 'Component', value: c)]
        build 'Run'
        build 'Reporting'
    }
}

Then make a map of all the closures you want to run simultaneously:

def jobs = [:]
def components = params.Componets.split(",")
for (int i = 0; i < components.size(); ++i) {
    def component = components[i].trim()
    jobs[component] = {
        oneNode(component)
    }
}

And finally use the parallel step with the resulting map:

stage('Build, run, report') {
    <the code from the above steps>
    parallel jobs
}