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Last week I participated in the Jenkins & Java 10 Online Hackathon. It was my first Jenkins hackathon and I roped in Jonah Graham to do some pair-programming. The hackathon featured JDK Project Jigsaw committers Mandy Chung and Paul Sandoz, as well as Jenkins creator Kohsuke Kawaguchi. It was a great opportunity for me to learn a lot about Jenkins and Java 10. Why Java 10? With the Java 8 EoL data looming, the focus was on the current available version of Java, Java 10. Java 10 offers some nice new features and APIs, not least improved docker container integration. We learned from Paul of a number of projects with Java 10 migration success stories including Elasticsearch, Kafka & Netty. At the beginning of the hackathon week, the Jenkins Pipeline feature would crash out when using Java 10. This was resolved with a number of fixes including the upgrade of the ASM library. Then it was nice to see things up and running with Java 10. Getting up & running The first steps were to do some exploratory testing using Jenkins with Java 10 via Docker, thanks to Oleg for providing clear instructions. This was boringly straightforward as most things worked and we only found one issue to report. Next to try to get some patches in, we needed to set-up a dev environment. The live session gave us what we needed to set up a plugin or core dev environment. One open question we had was whether Jenkins has semantic versioning and API tools to help identify when you might be breaking backwards compatibility. Overall it was straightforward to get a dev environment up and running. Java 10 New APIs The next step was to find an issue which we could help resolve. Many of the Java 10 issues were related to 'Illegal reflective access' from various plugins or third-party libraries. However after investigating a couple, removing these warnings required a good architectural knowledge of the plugin or core code itself. In the end we decided that messing around with classloaders or attempting to upgrade version of jdom was not one for the newbies. Instead we looked at removing reflection in cases of isAccessible calls. We found the ProcessHandle api very useful and a good replacement for some misuse of reflection, and even better it made the code work on Windows too. Mandy also pointed us to look at the Lookup api as possible alternate to findClass calls. Multi-Release JAR Builds Using new APIs is all well and good but presents a problem when you want to maintain backwards compatibility with Java 8. Hence the need for some sort of multi-jar solution - Nicolas De loof proposed one such solution for multi-release jars with Maven for this case. sun.misc.Signal The Java Signal API is being deprecated, but so far no replacement APIs are available for signal handling. Jenkins makes use of the Signal APIs so a big question for the Jigsaw team was whether this would be replaced going forward. Kohsuke pointed out how it is important for Java to maintain this UNIX like behaviour as it shouldn’t matter to end users that Jenkins is written in Java. It seems these APIs will be replaced in due course, they just aren’t there right now. Collaboration, Collaboration, Collaboration It was great to have the discussions with the Jigsaw team. They reminded us how they need to know the Java use cases out there and how their team uses these to feed into their development process. In turn, the hackathon had Jenkins community members participate, for instance easy-jenkins was up and running with Java 10 by the end of the week. The hackathon had a great feeling of community spirit and was a reminder why collaborations with communities and also between different communities can be powerful and fun for all involved. At the end of the week Jonah and I were both happy that we made our first Jenkins contributions (which were reviewed and merged quickly). Thanks to all who participated and made it highly enjoyable, especially Oleg for great organization. I look forward to the next one!

This week we have a Jenkins & Java 10 Online Hackathon. This is an open online event, where we work together on Jenkins core and plugins in order to find and fix compatibility issues, share experiences and have some fun. Everybody is welcome to join, independently of their Jenkins experience and amount of time they have available. After the kick off on Monday Jenkins contributors have been working on Java 10 and Java 11 support in Jenkins. We have already received contributions from 12 hackathon participants, and the number keeps growing. There are still 3 days ahead, but we have already achieved some important results we want to share. Jenkins Pipeline One of our major efforts over last 2 days was to get Jenkins Pipeline working on Java 10+. When the hackathon started Jenkins Pipeline was not working at all, and it was a major blocker for Java support and for exploratory testing in particular. We’ve been working together with Sam van Oort and Devin Nusbaum to fix the libraries in the Jenkins core, Pipeline: Support plugin and Docker packaging. Just to summarize the result of two days in one screenshot…​ Yes, we have got it running! Over two days we have got from the "Pipeline Crashes Immediately" state to the situation when the most of key Pipeline features are operational, including Scripted and Declarative Pipeline, Blue Ocean, shared libraries and dozens of plugins being used in the Jenkins plugin build flow. There is still a lot of work to do to get the changes finalized, but Jenkins Pipeline is available for testing on Java 10 and 11 now. If you want to try it out, you can use a new jenkins/jenkins-experimental:blueocean-jdk10 image we have created. It bundles all the required patches, so you can just run the following command to get started: docker run -p 8080:8080 -p 50000:50000 jenkins/jenkins-experimental:blueocean-jdk10 If you want to try more complex scenarions, see the Running Jenkins with Java 10 and 11 blogpost and List of Required patches. What else? Although Pipeline is the most visible change, there are other ongoing activities: Devin Nusbaum explored plugin startup issues we had with JDK 11ea+17 and confirmed that we need to upgrade our images to JDK 11ea+18 Gianpaolo Macario is working on adopting the Java 10 experimental images in his easy-jenkins project Sam van Oort and Devin Nusbaum are working on getting plugin build and test flows when using JDK 10 with Maven Nicolas de Loof is working on cleaning up Illegal reflective access warnings in Jenkins components, using the new Fields micro-library Olivier Lamy and Nicolas de Loof are updating the Animal Sniffer plugin for Maven to make it compatible with Java 9 and above Kohsuke Kawaguchi has released a repackaged version of ASM 6.2 we use in the project Last but not least, Liam Newman and Tracy Miranda helped us a lot to run the meetings and to get this hackathon organized There are also other contributors working on exploratory testing and reporting defects they discover. See our status doc for the full list. What’s next? Tomorrow we will have 2 sessions: At 8AM UTC we will have a sync-up. According to the requests from hackathon paticipants, we will have an intro session to Jenkins development for newcomers YouTube link At 4PM UTC we will have a meeting with key JDK Project Jigsaw committers Mark Reinhold, Mandy Chung and Paul Sandoz will join us to talk about Java 10/11 adoption YouTube link We will also post participant links in our Gitter channel 15 minutes before the meetings. If you have any questions, please join the meetings or raise questions in the chat during the call. Can I still join the hackathon? Yes, you can! It is possible to hop in and hop off at any time. Just respond to the registration form, join our Gitter channel and start hacking/testing. We also have a number of newbie-friendly issues you can start from. See our Kick-off session and slides for quick start guidelines. Links Developer mailing list Hackathon sync-up document Running Jenkins with Java 10 and 11 Jenkins Online Meetup page

Please refer to Running Jenkins on Java 11 documentation to have the up-to-date details on how to run Jenkins on Java 11. Guidelines in this blogpost are rendered obsolete by the Java 11 Support Preview Availability announcement on Dec 13, 2018 and by the Java 11 GA release on Sep 25, 2018. See the Java support page for up-to-date information about running Jenkins with Java 11. The Jenkins project also no longer ships preview versions for Java 10. As you probably know, we will have a Jenkins and Java 10+ online hackathon this week. In order to enable early adopters to try out Jenkins with new Java versions, we have updated Jenkins core and Docker packages. Starting from Jenkins 2.127, weekly releases can be launched with Java 10 and Java 11 (preview). Although there are some known compatibility issues, the packages are ready for evaluation and exploratory testing. This article explains how to run Jenkins with Java 10 and 11 using Docker images and WAR files. It also lists known issues and provides contributor guidelines. Running in Docker In order to simplify testing, we have created a new jenkins/jenkins-experimental repository on DockerHub. This repository includes various Jenkins Core images, including Java 10 and Java 11 images. We have also set up development branches and continuous delivery flows for Jenkins core, so now we can deliver patches for these images without waiting for weekly releases. You can run the image simply as: docker run -p 8080:8080 -p 50000:50000 jenkins/jenkins-experimental:latest-jdk11 The following tags are available: 2.127-jdk10, 2.128-jdk10 - Weekly releases packaged with Java 10 2.127-jdk11, 2.128-jdk11 - Weekly releases packaged with Java 11 latest-jdk10 - Jenkins core build from the java10-support branch latest-jdk11 - Automatic build from the core’s java11-support branch. blueocean-jdk10, blueocean-jdk11 - Experimental build, which bundles all Jenkins Pipeline and Blue Ocean patches required to run on Java 11. If you want to try Pipeline, use this image Java 10/11 images are fully compatible with the official jenkins/jenkins Docker image documentation, e.g. you can use plugins.txt to install plugins, mount volumes and pass extra options via environment variables. Running Jenkins without Docker Java 10 Download Jenkins WAR for 2.127 or above (or build the experimental branch) Run WAR with the following command: ${JAVA10_HOME}/bin/java --add-modules java.xml.bind -jar jenkins.war \ --enable-future-java --httpPort=8080 --prefix=/jenkins Java 11 Download Jenkins WAR for 2.127 or above (or build the experimental branch) Download the following libraries to the same directory as jenkins.war jaxb-api-2.3.0.jar (save as jaxb-api.jar) jaxb-core-2.3.0.1.jar (save as jaxb-core.jar) jaxb-impl-2.3.0.1.jar (save as jaxb-impl.jar) javax.activation v.1.2.0 (save as javax.activation.jar) Run the following command: Run Jenkins with ${JAVA11_HOME}/bin/java \ -p jaxb-api.jar:javax.activation.jar --add-modules java.xml.bind,java.activation \ -cp jaxb-core.jar:jaxb-impl.jar \ -jar jenkins.war --enable-future-java --httpPort=8080 --prefix=/jenkins Current state As of June 17, we have achieved the following state: Jenkins 2.127+ starts up successfully with OpenJDK 10.0.1 and OpenJDK 11+17-Debian-2 (preview) It is possible to configure and run simple Freestyle jobs Jenkins agents are able to start on Java 10, to connect to the controller and to execute Freestyle jobs Agents can be connected using Docker Plugin and Yet Another Docker Plugin Job DSL plugin works well on demo projects Maven Integration plugin can build plugin-pom -based Jenkins plugins when running on agents with JDK 8 It is possible to create Folders and manage items in them It is possible to configure Jenkins using Configuration-as-Code plugin Jenkins is able to execute Groovy scripts in Script Console and Groovy Hooks Known issues So far we know about the following issues: Pipeline crashes immediately on Java 10 and 11 ( JENKINS-46602) Workaround: Pipeline: Support plugin should be updated to version 3.0-java11-alpha-1-rc684.d802f5d9aeed from the Incrementals repo ( download) FIXED - Git Client plugin 2.7.2 cannot be installed when running with Java 11 build 18ea There are many warnings about Illegal reflective access during execution (linked in JENKINS-40689). In current Java 10 and 11 releases it does not lead to failures, but we want to cleanup these warnings anyway FIXED - Configuration-as-Code plugin fails to export configurations on Java 10 ( JENKINS-51991) We anticipate to discover and report more issues during the hackathon this week. Contributing If you discover incompatibilities in plugins, please report issues in our bugtracker. We have java10 and java11 labels for such issues. If you are interested to try out Jenkins with Java 10 and 11 before June 22nd, you may be interested to sign-up to the Jenkins and Java 10+ online hackathon. Everybody is welcome to join, independently of their Jenkins experience and amount of time they have available. Exploratory testing is also within the hackathon’s scope. During this event, please also use the java10_hackathon label. It will help us to track contributions and send folks some small "thank you" gifts for participating (details will be figured out during the hackathon). If you want to contribute patches to the core, please submit pull requests to java10-support or java11-support branches. If the patches are compatible with Java 8, we will try to upstream them to weekly releases. For plugin patches please create pull requests against main branches and then follow guidelines from plugin maintainers. If you need additional reviews and you are a member of the jenkinsci organization, feel free to mention the @jenkinsci/java10-support team in your PRs. Links: Docker: jenkins/jenkins-experimental images JIRA: Java 10 compatibility JIRA: Java 11 compatibility Jenkins and Java 10+ online hackathon

On behalf of the Jenkins Events Team, I would like to invite you to the “Jenkins & Java 10 Online Hackathon” which will take place from June 18th to 22nd. We will be working together on Jenkins core and plugins in order to find and fix compatibility issues, share experiences and have some fun. Everybody is welcome to join, independently of their Jenkins experience and amount of time they have available. If you are interested in participating in the hackathon, please sign-up in this form. Background Java 9 has recently been end-of-lifed, Java 10 is in GA, and Java 11 is in early beta. Jenkins project currently requires Java 8 to run reliably, and there are some known compatibility issues with higher Java versions. During the Jenkins World 2017 Hackathon, Mark Waite and Baptiste Mathus spent some time exploring Java 9 compatibility in Jenkins. We are currently tracking compatibility issues in the JENKINS-40689 EPIC, but there are likely many unknown issues in Jenkins core, plugins and in libraries we use in the project. We would like to continue their effort and work on Java 10+ support. Objectives and Scope As I have said above, the goals are to explore/fix compatibility issues, share experiences and have fun. We DO NOT plan to make Jenkins fully compatible with Java 10+ during the hackathon, but we will try to integrate fixes and make them available. Since the announcement of the Hackathon in the mailing list, we have got a number of registrations from contributors working on several project areas. We will split our work to several areas: Jenkins core and Remoting Pipeline Engine Plugins (e.g. Git plugin or any plugin you want to work on) Exploratory testing for Java 10 and beyond In order to organize the effort, we have created a java10_hackathon label in Jenkins JIRA. If you are interested in particular tasks, please assign them to yourself and add the label. Organization Currently the event is in the planning stage. We will be using the Developer mailing list for synchronization before the event. What will we have? Communications in #jenkins-hackhouse IRC and in the Jenkins Gitter channel Daily recorded sync-up calls in Hangouts Knowledge transfer sessions during the event We also want to prepare some special swag for active participants. If you have reached this part of the blogpost, you have probably seen the logo ;) Links Registration Developer mailing list Hackathon sync-up document Running Jenkins with Java 10 and 11 JIRA: Java 10 compatibility JIRA: Java 11 compatibility JIRA: Hackathon tasks