Using Executor in jruby

executor.rb

# Start the executor service.  Note that this won't create any threads right away,
# but will create new threads as the jobs are submitted, until it gets to 5 threads.
# Then it will reuse the threads.
executor = java.util.concurrent.Executors.newFixedThreadPool(5)

# Submit jobs, get back java.util.concurrent.FutureTask objects.
future_tasks = [1, 2, 3, 4, 5, 6].map do |number|
  executor.submit do
    puts "starting work"
    sleep(10)
    puts "done"
  end
end

# We get control back immediately, while the queries are being executed by the thread pool.
# We can do some other things here while the queries run.

# Get the results of all queries and combine them into an array.  FutureTask.get will wait
# for the task to complete if it's not completed yet, so it's safe to call this right away.
# If for some reason we wanted to check if a task is complete, we can call t.done? .
results = future_tasks.map do |future_task|
  begin
    # Max timeout for each thread is 10 seconds
    future_task.get(10, java.util.concurrent.TimeUnit::SECONDS)
  rescue java.util.concurrent.ExecutionException, java.util.concurrent.TimeoutException => e
    if e.is_a? java.util.concurrent.TimeoutException
      raise TimeoutError
    else
      # Convert the exception to one actually thrown inside the task.
      raise e.cause.exception
    end
  end
end

# Shut down the thread pool.
executor.shutdown_now

source: http://blog.bitmelt.com/2013/05/concurrent-tasks-in-jruby.html