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Filename : thread.rb
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#
#               thread.rb - thread support classes
#                       by Yukihiro Matsumoto <matz@netlab.co.jp>
#
# Copyright (C) 2001  Yukihiro Matsumoto
# Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
# Copyright (C) 2000  Information-technology Promotion Agency, Japan
#

unless defined? Thread
  raise "Thread not available for this ruby interpreter"
end

unless defined? ThreadError
  class ThreadError < StandardError
  end
end

if $DEBUG
  Thread.abort_on_exception = true
end

#
# ConditionVariable objects augment class Mutex. Using condition variables,
# it is possible to suspend while in the middle of a critical section until a
# resource becomes available.
#
# Example:
#
#   require 'thread'
#
#   mutex = Mutex.new
#   resource = ConditionVariable.new
#
#   a = Thread.new {
#     mutex.synchronize {
#       # Thread 'a' now needs the resource
#       resource.wait(mutex)
#       # 'a' can now have the resource
#     }
#   }
#
#   b = Thread.new {
#     mutex.synchronize {
#       # Thread 'b' has finished using the resource
#       resource.signal
#     }
#   }
#
class ConditionVariable
  #
  # Creates a new ConditionVariable
  #
  def initialize
    @waiters = {}
    @waiters_mutex = Mutex.new
  end

  #
  # Releases the lock held in +mutex+ and waits; reacquires the lock on wakeup.
  #
  # If +timeout+ is given, this method returns after +timeout+ seconds passed,
  # even if no other thread doesn't signal.
  #
  def wait(mutex, timeout=nil)
    Thread.handle_interrupt(StandardError => :never) do
      begin
        Thread.handle_interrupt(StandardError => :on_blocking) do
          @waiters_mutex.synchronize do
            @waiters[Thread.current] = true
          end
          mutex.sleep timeout
        end
      ensure
        @waiters_mutex.synchronize do
          @waiters.delete(Thread.current)
        end
      end
    end
    self
  end

  #
  # Wakes up the first thread in line waiting for this lock.
  #
  def signal
    Thread.handle_interrupt(StandardError => :on_blocking) do
      begin
        t, _ = @waiters_mutex.synchronize { @waiters.shift }
        t.run if t
      rescue ThreadError
        retry # t was already dead?
      end
    end
    self
  end

  #
  # Wakes up all threads waiting for this lock.
  #
  def broadcast
    Thread.handle_interrupt(StandardError => :on_blocking) do
      threads = nil
      @waiters_mutex.synchronize do
        threads = @waiters.keys
        @waiters.clear
      end
      for t in threads
        begin
          t.run
        rescue ThreadError
        end
      end
    end
    self
  end
end

#
# This class provides a way to synchronize communication between threads.
#
# Example:
#
#   require 'thread'
#
#   queue = Queue.new
#
#   producer = Thread.new do
#     5.times do |i|
#       sleep rand(i) # simulate expense
#       queue << i
#       puts "#{i} produced"
#     end
#   end
#
#   consumer = Thread.new do
#     5.times do |i|
#       value = queue.pop
#       sleep rand(i/2) # simulate expense
#       puts "consumed #{value}"
#     end
#   end
#
#   consumer.join
#
class Queue
  #
  # Creates a new queue.
  #
  def initialize
    @que = []
    @que.taint          # enable tainted communication
    @num_waiting = 0
    self.taint
    @mutex = Mutex.new
    @cond = ConditionVariable.new
  end

  #
  # Pushes +obj+ to the queue.
  #
  def push(obj)
    Thread.handle_interrupt(StandardError => :on_blocking) do
      @mutex.synchronize do
        @que.push obj
        @cond.signal
      end
    end
  end

  #
  # Alias of push
  #
  alias << push

  #
  # Alias of push
  #
  alias enq push

  #
  # Retrieves data from the queue.  If the queue is empty, the calling thread is
  # suspended until data is pushed onto the queue.  If +non_block+ is true, the
  # thread isn't suspended, and an exception is raised.
  #
  def pop(non_block=false)
    Thread.handle_interrupt(StandardError => :on_blocking) do
      @mutex.synchronize do
        while true
          if @que.empty?
            if non_block
              raise ThreadError, "queue empty"
            else
              begin
                @num_waiting += 1
                @cond.wait @mutex
              ensure
                @num_waiting -= 1
              end
            end
          else
            return @que.shift
          end
        end
      end
    end
  end

  #
  # Alias of pop
  #
  alias shift pop

  #
  # Alias of pop
  #
  alias deq pop

  #
  # Returns +true+ if the queue is empty.
  #
  def empty?
    @que.empty?
  end

  #
  # Removes all objects from the queue.
  #
  def clear
    @que.clear
  end

  #
  # Returns the length of the queue.
  #
  def length
    @que.length
  end

  #
  # Alias of length.
  #
  alias size length

  #
  # Returns the number of threads waiting on the queue.
  #
  def num_waiting
    @num_waiting
  end
end

#
# This class represents queues of specified size capacity.  The push operation
# may be blocked if the capacity is full.
#
# See Queue for an example of how a SizedQueue works.
#
class SizedQueue < Queue
  #
  # Creates a fixed-length queue with a maximum size of +max+.
  #
  def initialize(max)
    raise ArgumentError, "queue size must be positive" unless max > 0
    @max = max
    @enque_cond = ConditionVariable.new
    @num_enqueue_waiting = 0
    super()
  end

  #
  # Returns the maximum size of the queue.
  #
  def max
    @max
  end

  #
  # Sets the maximum size of the queue.
  #
  def max=(max)
    raise ArgumentError, "queue size must be positive" unless max > 0

    @mutex.synchronize do
      if max <= @max
        @max = max
      else
        diff = max - @max
        @max = max
        diff.times do
          @enque_cond.signal
        end
      end
    end
    max
  end

  #
  # Pushes +obj+ to the queue.  If there is no space left in the queue, waits
  # until space becomes available.
  #
  def push(obj)
    Thread.handle_interrupt(RuntimeError => :on_blocking) do
      @mutex.synchronize do
        while true
          break if @que.length < @max
          @num_enqueue_waiting += 1
          begin
            @enque_cond.wait @mutex
          ensure
            @num_enqueue_waiting -= 1
          end
        end

        @que.push obj
        @cond.signal
      end
    end
  end

  #
  # Removes all objects from the queue.
  #
  def clear
    super
    @mutex.synchronize do
      @max.times do
        @enque_cond.signal
      end
    end
  end

  #
  # Alias of push
  #
  alias << push

  #
  # Alias of push
  #
  alias enq push

  #
  # Retrieves data from the queue and runs a waiting thread, if any.
  #
  def pop(*args)
    retval = super
    @mutex.synchronize do
      if @que.length < @max
        @enque_cond.signal
      end
    end
    retval
  end

  #
  # Alias of pop
  #
  alias shift pop

  #
  # Alias of pop
  #
  alias deq pop

  #
  # Returns the number of threads waiting on the queue.
  #
  def num_waiting
    @num_waiting + @num_enqueue_waiting
  end
end

# Documentation comments:
#  - How do you make RDoc inherit documentation from superclass?