futures.rb

require "thread"

class Future
  attr_reader :exception, :cancelled

  def initialize(&block)
    @thread = Thread.new(&block)
    @thread.abort_on_exception = false
    @exception = nil
    @cancelled = false
  end

  def running?
    @thread.alive?
  end

  def cancelled?
    @cancelled
  end

  def done?
    [email protected]?
  end

  def cancel
    @cancelled = true
    @thread.kill
  end

  def result(limit=nil)
    value(limit)
  rescue Exception => e
    @exception = e
    nil
  end

  def exception(limit=nil)
    result(limit)
    @exception
  end

private
  def value(limit)
    if @thread.join(limit)
      @thread.value
    else
      nil
    end
  end
end

q = Queue.new

future = Future.new { q.pop; raise "ZOMG" }

Thread.new { sleep 1; q.push "value" }

puts "HI!"

p future.result
p future.exception

puts "BYE!"