This simple JRuby program demonstrates a memory leak.

Try it yourself!

• mvn compile
• mvn exec:exec
• Note that -Xmx128m [is specified in pom.xml.] (https://github.com/KevinCorcoran/jruby-memory-leak/blob/master/pom.xml#L31)
• Monitor the memory usage of the process you just started.
  • ./watchpidmem.sh 1
    • This starts a script that periodically (every 1 second) prints the memory usage of the process.
    • The third column in the output, under the RES heading, is the resident memory usage of the process.
• Notice that the memory consumption of the process quickly and greatly exceeds the specified maximum heap size!

Notes

• Downgrading to JRuby 1.7.12 fixes the leak!
• Removing either Gem.clear_paths or the other 4 lines of ruby code prevents the leak from occurring.
• Changing Gem.clear_paths to some other method call also prevents the leak from occurring.
• Switching the order of the two statements in the ruby program does not affect the behavior.
• Moving the infinite loop out of java and into ruby does not affect the behavior.
• Putting sleep statements in the ruby code makes the program consume memory more slowly, but does not seem to prevent it from consuming more than it should.
• Here is a graph of memory usage over time of 2 separate runs of this program. Note that peak memory usage approached 2 GB on a 128 MB heap, and 8 GB on a 1 GB heap.