fastimage/lib/fastimage/fbr.rb

# Poor Man's Fiber (API compatible Thread based Fiber implementation for Ruby 1.8)
# (c) 2008 Aman Gupta (tmm1)

unless defined? Fiber
  require 'thread'

  class FiberError < StandardError; # :nodoc:
  end

  class Fiber # :nodoc:
    def initialize
      raise ArgumentError, 'new Fiber requires a block' unless block_given?

      @yield = Queue.new
      @resume = Queue.new

      @thread = Thread.new{ @yield.push [yield(*@resume.pop)] }
      @thread.abort_on_exception = true
      @thread[:fiber] = self
    end
    attr_reader :thread

    def resume *args
      raise FiberError, 'dead fiber called' unless @thread.alive?
      @resume.push(args)
      result = @yield.pop
      result.size > 1 ? result : result.first
    end

    def yield *args
      @yield.push(args)
      result = @resume.pop
      result.size > 1 ? result : result.first
    end

    def self.yield *args
      if fiber = Thread.current[:fiber]
        fiber.yield(*args)
      else
        raise FiberError, 'not inside a fiber'
      end
    end

    def self.current
      if Thread.current == Thread.main
        return Thread.main[:fiber] ||= RootFiber.new
      end

      Thread.current[:fiber] or raise FiberError, 'not inside a fiber'
    end

    def inspect
      "#<#{self.class}:0x#{self.object_id.to_s(16)}>"
    end
  end

  class RootFiber < Fiber # :nodoc:
    def initialize
      # XXX: what is a root fiber anyway?
    end

    def self.yield *args
      raise FiberError, "can't yield from root fiber"
    end
  end
end