Environment

JRuby: JRuby 9.0.5.0
OS: OSX 10.11.1

We don't set JRUBY_OPTS. For a change we're running this using the command-line instead of embedding it. We're basically firing up rspec as part of functional testing. None of our command-line options are for changing behaviour in JRuby, other than deliberately setting file.encoding=UTF-8 for the benefit of Windows, which is not relevant for this run here as I'm on OSX.

Gems: rspec-core, rspec-mocks, ci-reporter.

Other environment variables of Ruby relevance:

RBENV_ROOT=/Users/tester/DevEnv/rbenv
RBENV_SHELL=bash

rbenv is indeed present, although we are not using it when running the tests - the tests run by <java classname="org.jruby.Main"> from an Ant task.

Expected Behaviour

I have a spec written as follows:

it 'notifies the callback of each result' do
  callback = double(:callback)
  expect(callback).to receive(:found).exactly(24).times
  @thing.search('mime-type:message/rfc822', callback)
end

Of note, this Thing#search method internally performs work in a thread pool, so the callback gets called from multiple threads, possibly all simultaneously. So the issue I'm about to describe could be a thread safety bug.

Of course I expect this test to pass. ;)

(But due to other circumstances, the test fails about half the time, because this search method ultimately calls the callback on multiple threads and rspec-mocks is not thread-safe. That's another issue and not what I'm reporting here.)

Actual Behaviour

Occasionally (1 per 20 runs or so, based on today's runs), I get this failure instead:

 [java] Failures:
 [java] 
 [java]   1) Thing#search when a callback is provided notifies the callback of each result
 [java]      Failure/Error: Unable to find org.jruby.RubyArray.map(org/jruby/RubyArray.java to read failed line
 [java] 
 [java]      Java::JavaLang::ArrayIndexOutOfBoundsException:
 [java]        7
 [java]      # org.jruby.RubyArray.map(org/jruby/RubyArray.java:2300)
 [java]      # RUBY.(root)(/path/to/project/functional-tests/src/test/rspec/lib/case/search_unsorted_spec.rb:42)
 [java]      # RUBY.run(uri:classloader:/gems/rspec-core-3.4.3/lib/rspec/core/example.rb:236)
 [java]      # RUBY.with_around_and_singleton_context_hooks(uri:classloader:/gems/rspec-core-3.4.3/lib/rspec/core/example.rb:478)
 [java]      # RUBY.block in with_around_example_hooks(uri:classloader:/gems/rspec-core-3.4.3/lib/rspec/core/example.rb:435)
  ...

Line 42 is this one:

      @thing.search('mime-type:message/rfc822', callback)

No call to Array#map on that line, no array lookups either, no idea what is going on.