Developing OpenJDK Mission Control

The last blog (about Fetching and Building OpenJDK Mission Control) earned me questions on how to get the source into Eclipse to start playing around with it. This blog post will assume that you have first successfully completed the steps in the Fetching and Building OpenJDK Mission Control blog post.

Getting Eclipse

First of all you should download the latest version of Eclipse. JMC is an RCP application, and thus, the easiest way to make changes to it, is to use the Eclipse IDE.

There are various Eclipse bundles out there. Get (at least) the Eclipse IDE for Eclipse Committers. It adds some useful things, like PDE (the Plugin Development Environment), Git, the Marketplace client and more. You can also use the Eclipse IDE for Java Enterprise Developers.

You will need an Eclipse 2018-12 or later!

To get to the screen where you can select another packaging than the standard, click on the Download Packages link on the Eclipse download page.

Install it, start it and create a new workspace for your JMC work. Creating a new workspace is as easy as picking a new name when starting up your Eclipse in the dialog asking for a directory for the workspace:

Installing JDKs

Since you’ve already built JMC outside of the IDE, you already have a JDK 8. You probably also want to have a JDK 11 set up in your Eclipse.

Download and install a JDK11, then open Window | Preferences and then select Java / Installed JREs. Add your favourite JKD 8 and JDK 11 JDKs (Add…) and then use Java / Installed JREs / Execution Environments to set them as defaults for the JDK 8 and JDK 11 execution environments.

Note to JMC lovers:

You may want to ensure that a JDK is used to run your Eclipse, and not a jre. A JDK is needed for JMC to find the tools.jar, where the classes required for JMC to discover locally running JVMs are located. Simply add the –vm flag in your eclipse.ini file, and point it to your JDK:


Setting installed JREs:


Setting execution environments:


Okay, we now have our JDKs set up. Next step is to set up a user library for things that JMC will need from the JDK. This is directly from the JMC readme:

If importing the application projects, make sure you create a user library (Preferences | Java/Build Path/User Libraries) named JMC_JDK, and add (Add External JARs…) the following JARs from a JDK 8 (u40 or above) to the User Library: tools.jar (/lib/tools.jar), jconsole.jar (/lib/jconsole.jar), jfxswt.jar (/jre/lib/jfxswt.jar), and finally the jfxrt.jar (/jre/lib/ext/jfxrt.jar).

Creating the user library:


Adding the jars:


Now we need to check a few things…


Is the Jetty server from the previous blog up and running?

If yes, go ahead and open up the target file available under releng/platform-definitions/platform-definition-photon (File | Open File). You should see something like this:


Click the Set as Active Target Platform link in the upper right corner.

Now there is one final preparation for the import – we need to turn of certain Maven settings. Go to the preferences, and select Maven / Errors/Warnings. Set Plugin execution not covered by lifecycle configuration to Ignore, and also Out-of-date project configuration to Ignore


Now the preparations are done, and we can start importing the projects. Woho!

Importing the Projects

First we will have to import the core projects, since they are built separately from the rest. Select File | Import… and select Maven / Existing Maven Project.

Click next, and browse into the jmc/core folder. Select all the core projects and import them. (You may want to skip the top level poms.)

Next select File | Import… and select Maven / Existing Maven Project again, but this time from the root:

Again, you may want to skip the top level poms (/pom.xml, application/pom.xml etc), and the uitests (at least until we fix so that the jemmy dependency can be downloaded from Maven Central).

Next we will import the project which contains the launchers. Select File | Import… and then select Existing Projects into Workspace. Find the configuration/ide/eclipse folder and click Ok.


After importing that project, we can now launch JMC from within Eclipse:


Or run it in debug mode:


Configuring Development Settings

If you don’t plan on submitting any changes, then this step is optional. The team use shared settings for formatter and macros. Go to the preferences and then to Java / Code Style / Formatter. Then click Import… and select the configuration/ide/eclipse/formatting/formatting.xml. You should now have the Mission Control formatting settings active:



If you have the spotbugs plug-in installed, you should also import the spotbugs excludes (configuration/spotbugs/spotbugs-exclude.xml). There is also a common dictionary (configuration/ide/eclipse/dictionary/dictionary.txt) and templates (configuration/ide/eclipse/templates/JMC templates.xml) which you may find useful.

Adding (and Launching with) Some Custom Plug-in

The flame graph view may be included in JMC at some point. If so, then there will probably be some other plug-in somewhere that will serve as an example.

First install Git. If you, on the command line, can run git –version, you’re all set.

Next go to your git folder (or wherever you keep your git projects) and clone the jmc-flame-view repo:

git clone

Next go to Eclipse and do File | Import…, and select Existing Projects into Workspace. Select your jmc-flame-view folder, and click Finish:


Next we need a launcher which includes this new feature. Go to the org.openjdk.jmc.eclipseonfig project and open the launchers folder. Copy and paste the JMC RCP plug-ins.launch file. Name the copy something.


Click the run dropdown and select Run Configurations….


Select your new launcher, and click the Plug-ins tab. Add the new Flame Graph feature:


Click Apply and Run. Mission Control will start, with your new plug-in available. In the started JMC, go to Window | Show View | Other…. Select Mission Control / Flame Graph in the Show View dialog. Open a Flight Recording, and click on something that would yield an aggregated stack trace, such as something in the Method Profiling page, or a class in the Memory page – you should now see a Flame Graph of your selection.


This blog post explained, in some detail, how to import the OpenJDK Mission Control project into Eclipse, and how to set up the workspace to work on the code. It also explained how to run the code with an additional plug-in from a separate repo.

As always, please let me know if I forgot to mention something (except for the agent, which I will deal with in a separate post)!

Fetching and Building OpenJDK Mission Control

(Please note that an updated version of this article, for JMC 8+, is available here:

Since people keep asking me, I thought I’d put together this quick primer on how to get started with OpenJDK Mission Control. Now, once the early access builds of JMC 7 is out, that will probably be the easiest way to get started for people who don’t want to change stuff. This blog, however, will be for the ones of you who would like to build JMC from source.

Getting Mercurial

First step is to get Mercurial, the SCM used for OpenJDK. JMC (being an OpenJDK project) is available through a Mercurial repository. Installing Mercurial is different for different platforms:

Mac OS X

Easiest is to install through Homebrew:

brew install mercurial

That said, dmg packages can also be downloaded from here:


Go to Download the InnoSetup based installer and run it. Ensure that the “add to path” checkbox is checked. Verify that the install went fine by opening a command prompt and typing hg and enter. A list of the available commands should be printed.


For Debian based distributions, you can install using the package manager:

sudo apt-get install mercurial

That said, you can also get rpms and other installation packages from here:

Cloning the Source

Once Mercurial is installed properly, getting the source is as easy as cloning the jmc repo. First change into the directory where you want to check out jmc. Then run:

hg clone

Getting Maven

Since you probably have some Java experience, you probably already have Maven installed on your system. If you do not, you now need to install it. Simply follow the instructions here:

Building Mission Control

First we need to ensure that Java 8 is on our path. Some of the build components still use JDK 8, so this is important.

java –version

This will show the Java version in use. If this is not a Java 8 JDK, change your path. Once done, we are now ready to build Mission Control. Open up two terminals. Yep, two!

In the first one, go to where your cloned JMC resides and type in and execute the following commands (for Windows, replace the dash (/) with a backslash (\)):

cd releng/third-party
mvn p2:site
mvn jetty:run

Now, leave that terminal open with the jetty running. Do not touch.

In the second terminal, go to your cloned jmc directory. First we will need to build and install the core libraries:

cd core
mvn install

Next run maven in the jmc root:

mvn clean package

JMC should now be building. The first time you build Maven will download all of the third party dependencies. This will take some time. Subsequent builds will be less painful. On my system, the first build took 6:01 min. The subsequent clean package build took 2:38.

Running Mission Control

To start your recently built Mission Control, run:


target\products\org.openjdk.jmc\win32\win32\x86_64\jmc.exe -vm %JAVA_HOME%\bin

Mac OS X

target/products/org.openjdk.jmc/macosx/cocoa/x86_64/JDK\ Mission\ -vm $JAVA_HOME/bin

Contributing to JDK Mission Control

To contribute to JDK Mission Control, you need to have signed an Oracle Contributor Agreement. More information can be found here:

Don’t forget to join the dev list:

If there is interest, I will add a more detailed blog post on this later.

More Info

For more information on how to run tests, use APIs etc, there is a file in the root of the mercurial repo. Let me know in the comments section if there is something you think I should add to this blog post and/or the README!