Example using the AWS SDK v1 to demonstrate leaked memory under JRuby 9.1.15.0

Gemfile

source 'https://rubygems.org'

gem 'aws-sdk-v1'

test.rb

# Polls the AWS SimpleWorkflow service, doing nothing with the results
# 
# Under JRuby 9.1.15.0 something in the AWS SDK leaks memory (a single
# instance of org.jruby.util.io.FilenoUtil builds an ever-growing 
# collection of entries in the filenoMap attribute).
#
# There is no leak in earlier versions of JRuby including 9.1.14.0.
#
# HOW TO USE:
#
# 1. Get AWS credentials with access to the SimpleWorkflow service
#    (access_key_id, secret_access_key, and a region to use)
#
# 2. Use bundler to install the AWS SDK gem
#
# 3. Run the program under JRuby (tested with the following settings):
#    AWS_ACCESS_KEY_ID="<id>" AWS_SECRET_ACCESS_KEY="<key>" AWS_REGION=<region>
#      jruby -G --server -U -J-Xmx500M -J-Xms500M -J-XX:+UseG1GC
#      -J-XX:MaxGCPauseMillis=200 -J-XX:+UseStringDeduplication test.rb
# 
require 'aws-sdk-v1'

AWS_CONFIG = {
  access_key_id: ENV['AWS_ACCESS_KEY_ID'],
  secret_access_key: ENV['AWS_SECRET_ACCESS_KEY'],
  region: ENV['AWS_REGION'] || 'us-west-2'
}

SWF_DOMAIN = 'memory-leak-test-20180327'

def log(msg)
  puts "#{Time.now} Thread #{Thread.current.object_id} - #{msg}"
end

def test_polling
  AWS.config AWS_CONFIG

  swf = AWS::SimpleWorkflow.new
  domain = swf.domains[SWF_DOMAIN]
  domain = swf.domains.create(SWF_DOMAIN, 1) unless domain.exists?
  client = AWS::SimpleWorkflow::Client::V20120125.new
  threads = []

  10.times do |i|
    threads << Thread.new do
      log "started"
      loop do
        begin
          client_opts = {
            domain: domain.name,
            identity: "memory-leak-test-20180327-thread#{i}",
            task_list: { name: 'non-existent-task-list-for-test' },
            maximum_page_size: 1000,
            reverse_order: false
          }
          log "polling for SimpleWorkflow decision task"
          client.poll_for_decision_task(client_opts)
          log "poll complete"
        rescue => e
          log "rescued exception #{e}"
          # avoid tight loop if poll is immediately failing
          sleep 10
        end
      end
    end
  end

  # wait for all threads to exit (even though they won't)
  threads.each do |thread|
    thread.join
  end
end

test_polling

unhappy_heap.png

Example heap dump: https://www.dropbox.com/s/l3xw01a8xplw6ai/heapdump-1522190629819-memleak-test-jruby9.1.15.0-1.hprof.zip?dl=0