Add a nice little blog post about the despised JENKINS-26481

jenkins-infra · Sep 7, 2017 · 3ed6f84 · 3ed6f84
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+---
+layout: post
+title: "Closure on enumerators in Pipeline"
+tags:
+- pipeline
+- jenkinsworld
+author: rtyler
+---
+
+While at Jenkins World, link:https://github.com/kohsuke[Kohsuke Kawaguchi]
+presented two long-time Jenkins contributors with a
+"link:https://en.wikipedia.org/wiki/Small_matter_of_programming[Small Matter of Programming]"
+award: link:https://github.com/abayer[Andrew Bayer] and
+link:https://github.com/jglick[Jesse Glick]. "Small Matter of Programming"
+being:
+
+[quote, Wikipedia]
+____
+a phrase used to ironically indicate that a suggested feature or design change
+would in fact require a great deal of effort; it often implies that the person
+proposing the feature underestimates its cost.
+____
+
+In this context the "Small Matter" relates to link:/doc/book/pipeline[Jenkins
+Pipeline] and a very simple snippet of Scripted Pipeline:
+
+[source,groovy]
+----
+[1, 2, 3].each { println it }
+----
+
+For a long time in Scripted Pipeline, this simply did not work as users would
+expect it. Originally filed as
+link:https://issues.jenkins-ci.org/browse/JENKINS-26481[JENKINS-26481] in 2015,
+it became one of the most voted for, and watched, tickets in the entire issue
+tracker until it was ultimately fixed earlier this year.
+
+image::https://farm5.staticflickr.com/4421/36886763192_1ae5a04428.jpg[Photo by Kohsuke, role=center, link=https://www.flickr.com/photos/12508267@N00/36886763192/]
+
+
+[quote, Original bug description by Daniel Tschan]
+____
+At least some closures are executed only once inside of Groovy CPS DSL scripts
+managed by the workflow plugin.
+____
+
+At a high level, what has been confusing for many users is that Scripted
+Pipeline looks like a Groovy, it quacks like a Groovy, but it's not _exactly_
+Groovy. Rather, there's an custom Groovy interpreter
+(link:https://github.com/jenkinsci/workflow-cps-plugin[CPS]) that executes the
+Scripted Pipeline in a manner which provides the durability/resumability that
+defines Jenkins Pipeline.
+
+Without diving into too much detail, refer to the pull requests linked to
+JENKINS-26481 for that, the code snippet above was particularly challenging to
+rectify inside the Pipeline execution layer. As one of the chief architects for
+Jenkins Pipeline, Jesse made a number of changes around the problem in 2016,
+but it wasn't until early 2017 when Andrew, working on Declarative Pipeline,
+started to identify a number of areas of improvement in CPS and provided
+multiple patches and test cases.
+
+
+As luck would have it, combining two of the sharpest minds in the Jenkins
+project resulted in the "Small Matter of Programming" being finished, and
+released in May of this year with plugin:workflow-cps[Pipeline: Groovy] 2.33.
+
+
+Please join me in congratulating, and thanking, Andrew and Jesse for their
+diligent and hard work smashing one of the most despised bugs in Jenkins
+history :).