Jenkins Parallel Build reads in an empty map, but it held data in a previous stage - jenkins

Question

Total noobie trying to make a parallel build more dynamic.
Using this declarative script https://stackoverflow.com/a/48421660/14335065
instead of reading in a prepopulated map def jobs = ["JobA", "JobB", "JobC"], which works perfectly.
I am trying to read in from a global map variable JOBS = [] which I populate in a stage using JOBS.add("JobAAA") syntax.
Printing out JOBS in a pipeline stage shows there are contents within,
JOBS map is [JobAAA, JobBBB, JobCCC]
but when I use it to generate a parallel build it seems to become empty and I am getting error message
No branches to run
I know I must be mixing my understands up somewhere, but can anyone please point me in the right direction.
Here is the code I am fighting with
def jobs = ["JobA", "JobB", "JobC"]
JOBS_MAP = []
def parallelStagesMap = jobs.collectEntries() {
["${it}" : generateStage(it)]
}
def parallelStagesMapJOBS = JOBS_MAP.collectEntries(){
["${it}" : generateStage(it)]
}
def generateStage(job) {
return {
stage("Build: ${job}") {
echo "This is ${job}."
}
}
}
pipeline {
agent any
stages {
stage('populate JOBS map') {
steps {
script {
JOBS_MAP.add("JobAAA")
JOBS_MAP.add("JobBBB")
JOBS_MAP.add("JobCCC")
}
}
}
stage('print out JOBS map'){
steps {
echo "JOBS_MAP map is ${JOBS_MAP}"
}
}
stage('parallel job stage') {
steps {
script {
parallel parallelStagesMap
}
}
}
stage('parallel JOBS stage') {
steps {
script {
parallel parallelStagesMapJOBS
}
}
}
}
}

Answer 1

Try this:
def jobs = ["JobA", "JobB", "JobC"]
JOBS_MAP = []
def generateStage(job) {
return {
stage("Build: ${job}") {
echo "This is ${job}."
}
}
}
pipeline {
agent any
stages {
stage('populate JOBS map') {
steps {
script {
JOBS_MAP.add("JobAAA")
JOBS_MAP.add("JobBBB")
JOBS_MAP.add("JobCCC")
}
}
}
stage('print out JOBS map'){
steps {
echo "JOBS_MAP map is ${JOBS_MAP}"
}
}
stage('parallel job stage') {
steps {
script {
def parallelStagesMap = jobs.collectEntries() {
["${it}" : generateStage(it)]
}
parallel parallelStagesMap
}
}
}
stage('parallel JOBS stage') {
steps {
script {
def parallelStagesMapJOBS = JOBS_MAP.collectEntries(){
["${it}" : generateStage(it)]
}
parallel parallelStagesMapJOBS
}
}
}
}
}