Fun with cuncurrency in jruby

futures.rb

class Future
  include java.util.concurrent.Callable

  @@executor = java.util.concurrent.Executors::newFixedThreadPool(5)

  def initialize(&block)
    @block = block
  end

  def on_success(&block)
    @on_success = block

    self
  end

  def on_error(&block)
    @on_error = block

    self
  end

  def run
    @future = @@executor.submit(self)
  end

  def get
    @future.get
  end

  def call
    result = begin
               @block.call
             rescue Exception => e
               @on_error.call(e) unless @on_error.nil?
               raise e
             end

    @on_success.call unless @on_success.nil?

    result
  end

  def self.pool_size=(num)
    @@executor.core_pool_size = num
  end

  def self.pool_size
    @@executor.core_pool_size
  end
end

f = Future.new { sleep 1; puts "1"; 1 }

f.on_success do
  puts 'everything is fine!'
end.on_error do |e|
  puts 'error!'
end

f.run

f.get

you need to submit the Callable and not the block (getting "caster" to another Callable) :
@future = @@executor.submit(self)

Thanks! :)