Java Mission Control — On OS X

Java Mission Control (or JMC) is a tool for tapping into Java tools and capture data, in order to analyze various metric and to do profiling.

On OS X it’s possible to just run ‘jmc’ on the command line and start it. However, it’s also nice to have an icon for it, isn’t it? Here’s a wrapper I created for Java Mission Control. The script auto detects your latest Java version.

Start Script Editor and create an Application with the following source code:

set javaHome to do shell script "/usr/libexec/java_home"
set jmcApp to javaHome & "/lib/missioncontrol/Java Mission Control.app"
run application jmcApp

I saved it as an Application and placed it in /Applications. I then replaced the applet.icns file inside the bundle with this file (shared via Google Drive):

https://drive.google.com/file/d/0B_7NRJWc_ISJdWlwYzQyMEdISkU/view?usp=sharing

I moved it to my Dock and it now looks like this (left).

Let’s try it out!

I created a little sample program that simply adds a heck of a lot of data to the heap.

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class Main {
    public static void main(String[] args) {
        final List<String> list = new ArrayList<>();
        final Random r = new Random();

        while (true) {
            list.add(r.nextInt() + " ID");
            list.addAll(list);
            System.out.println("List is now " + list.size() + " elements long");

            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

Run the program with the following JVM flags, otherwise it won’t work.

-XX:+UnlockCommercialFeatures -XX:+FlightRecorder

I found the PID, and ran this on the command line:

$ jcmd 49804 JFR.start duration=120s filename=2min.jfr

This generates 2 minutes worth of Flight Recorder data that can be opened by Java Mission Control. Now I can inspect memory, code, threads, I/O, CPU and other general metrics.

Stay tuned for the next article where I’ll follow up on Java Mission Control and Flight Recorder.