semaphore.rb

semaphore.rb

# = Semaphore
#
# Technically a semaphore is simply an integer variable which
# has an execution queue associated with it.
#
# Copyright (c) 2005 Fukumoto

class Semaphore

  def initialize(initvalue = 0)
    @counter = initvalue
    @waiting_list = []
  end

  def wait
    Thread.critical = true
    if (@counter -= 1) < 0
      @waiting_list.push(Thread.current)
      Thread.stop
    end
    self
  ensure
    Thread.critical = false
  end

  def signal
    Thread.critical = true
    begin
      if (@counter += 1) <= 0
        t = @waiting_list.shift
        t.wakeup if t
      end
    rescue ThreadError
      retry
    end
    self
  ensure
    Thread.critical = false
  end

  alias_method( :down, :wait )
  alias_method( :up,   :signal )
  alias_method( :p,    :wait )
  alias_method( :v,    :signal )

  def exclusive
    wait
    yield
  ensure
    signal
  end

  alias_method( :synchronize, :exclusive )

end