Contents

=begin rdoc

= Semaphore (CountingSemaphore)

Technically a semaphore is simply an integer variable which
has an execution queue associated with it.

== Usage

  s = Semaphore.new

  # to do
  
== History
 
  $Id: semaphore.rb,v 1.2 2003/03/15 20:10:10 fukumoto Exp $

=end

class CountingSemaphore

  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

Semaphore = CountingSemaphore

Version data entries

1 entries across 1 versions & 1 rubygems

Version	Path
carats-0.3.0	lib/carat/semaphore.rb