Macruby Fibers using GCD (transfer method implemented, 'double resume' error needs implementing)

macruby_fiber.rb

class FiberError < StandardError; end

class Fiber
  attr_accessor :name
  def initialize &block
    raise ArgumentError, 'new Fiber requires a block' unless block_given?
    @block = block
    
    @yield_sem = Dispatch::Semaphore.new(0)
    @resume_sem = Dispatch::Semaphore.new(0)
    
    @fiber_queue = Dispatch::Queue.new "#{__id__}"
    @fiber_queue.async {@yield_sem.wait}
    Fiber[@fiber_queue.label]= self

    execute_block
  end
  
  private
  def execute_block
    @completed = false
    @fiber_queue.async do 
      @result ||= @block.call(*@args)
      unless self == Fiber[:root_fiber]
        Fiber.delete_fiber(@fiber_queue.label)
        @block = nil # when @block becomes nil the fiber is dead
      end
      @completed = true
      @resume_sem.signal
      @result
    end
  end
  
  public
  def resume *args
    raise FiberError, 'dead fiber called' if @block.nil?
    # raise FiberError, 'double resume' if @has_transferred == true
    
    execute_block if @completed # root fiber never dies
    
    if @args.nil?
      @args = args
    else
      @result = args.size > 1 ? args : args.first
    end

    @yield_sem.signal
    @resume_sem.wait unless @has_transferred == :complete
    @result
  end

  # yield is called from inside the block passed to Fiber.new and executes within the @fiber_queue
  def yield *args
    @result = args.size > 1 ? args : args.first
    @resume_sem.signal
    @yield_sem.wait
    @result
  end
  
  def transfer *args
    fiber = Fiber.current # the fiber in whose context the transfer call was made. Should be given a yield call to suspend execution of its block
    @transferred_from = fiber

    if Fiber[:root_fiber] == fiber # check for transfer to root fiber
      self.resume *args
    else
      resume = lambda do |previous_fiber|
        @has_transferred = :complete if self == previous_fiber && !previous_fiber.nil? 
        self.resume *args
      end
          
      fiber.instance_eval do
        @has_transferred = true
        self.yield *resume.call(@transferred_from)      
        @resume_sem.wait and @has_transferred = nil if @has_transferred == :complete
      end
    end
  end
  
  def alive?
    [email protected]?
  end
  
  def inspect
    "#<#{self.class}:0x#{self.object_id.to_s(16)}>"
  end
  
  def self.current
    Fiber[Dispatch::Queue.current.label] || Fiber[:root_fiber]
  end
  
  def self.yield *args
    raise FiberError, "can't yield from root fiber" unless fiber = Fiber[Dispatch::Queue.current.label]
    fiber.yield *args
  end
  
  # class methods to get, set and delete fiber references
  # wrapped with a serial queue for safe multi-threaded use
  def self.[] fiber_id
    @@fibers_queue.sync { return @@__fibers__[fiber_id] }
  end
  
  def self.[]= fiber_id, fiber
    @@fibers_queue.sync { @@__fibers__[fiber_id]= fiber }
  end
  
  def self.delete_fiber fiber_id
    @@fibers_queue.sync { @@__fibers__.delete(fiber_id) }
  end
  
  @@__fibers__ = {} # create class hash to enable look-up of individual fibers when using 'Fiber.yield'
  @@fibers_queue = Dispatch::Queue.new('fibers_queue') # create serial queue to access class hash
  Fiber[:root_fiber]= Fiber.new { |*args| args.size > 1 ? args : args.first } # create root fiber. Default behaviour is to return arguments it receives
end

macruby_fiber_tests.rb

require 'minitest/autorun'

describe "try to create new fiber without block" do
  it "should raise ArgumentError" do
    proc { Fiber.new }.must_raise ArgumentError
  end
end

## Attempting to run the following test crashes macruby ##

# describe "get root fiber" do
#   it "should be fiber" do
#     f = Fiber.current
#     f.must_be_instance_of Fiber
#   end
# end

describe "return default value from resumed fiber" do
  it "should return final value from fiber" do
    fiber = Fiber.new { 1; 2; 'return from fiber' }
    fiber.resume.must_equal 'return from fiber'
  end
end

describe "return single value from resume" do
  it "should return arg to resume from fiber" do
    fiber = Fiber.new {|x| 1; 2; x }
    fiber.resume('fred').must_equal 'fred'
  end
end

describe "Setting variable inside and outside of fiber" do
  it "should set var and return last value in fiber block" do
    fiber = Fiber.new do |x|
      str = Fiber.yield(x)
      'fiber return value'
    end
    str = fiber.resume('first resume arg').must_equal 'first resume arg'
    fiber.resume('second resume arg').must_equal 'fiber return value'
    str.must_equal 'second resume arg'
  end
end

describe "fiber dies after returning final value" do
  it "should die after second resume and raise error on third resume" do
    fiber = Fiber.new { Fiber.yield('yield value'); 'fiber return value'}
    fiber.resume.must_equal 'yield value'
    fiber.resume.must_equal 'fiber return value'
    fiber.alive?.must_equal false
    proc { fiber.resume }.must_raise FiberError # dead fiber
  end
end

describe "yield value from fiber" do
  it "should return default value on first resume, nil on second, raise error on third" do
    fiber = Fiber.new { Fiber.yield "yield from fiber"}
    fiber.resume.must_equal "yield from fiber"
    fiber.resume.must_equal nil
    proc { fiber.resume }.must_raise FiberError # dead fiber
  end
end

describe "yield value from fiber with arg" do
  it "should return arg value on first and second resume, then raise error on third" do
    fiber = Fiber.new { |x| Fiber.yield x }
    fiber.resume('arg to first resume').must_equal 'arg to first resume'
    fiber.resume('arg to second resume').must_equal 'arg to second resume'
    proc { fiber.resume }.must_raise FiberError # dead fiber
  end
end

describe "yield value in loop" do
  it "should stay alive" do
    fiber = Fiber.new do
      start = 0
      loop do
        Fiber.yield start
        start += 1
      end
    end
    fiber.resume.must_equal 0
    fiber.resume.must_equal 1
    fiber.resume.must_equal 2
    fiber.alive?.must_equal true
  end
end

describe "yield value in loop - with resume arg" do
  it "fiber should stay alive" do
    fiber = Fiber.new do |start|
      loop do
        Fiber.yield start
        start += 1
      end
    end
    fiber.resume(10).must_equal 10
    fiber.resume.must_equal 11
    fiber.resume(57).must_equal 12 # because yield is called within a loop, the resume arg only applies on the first call
    fiber.alive?.must_equal true
  end
end

describe "Yield calculated value from resume arg" do
  it "should return altered arg value from first resume, unaltered arg value on second resume and raise error on third" do
    fiber = Fiber.new do |first|
      second = Fiber.yield first + 2
    end
    fiber.resume(10).must_equal 12
    fiber.resume(89).must_equal 89 # the second resume continues from where yield left off, therefore fiber returns arg to resume
    proc {fiber.resume(73)}.must_raise FiberError # dead fiber
  end
end