thwait.rb

#
#   thwait.rb - thread synchronization class
#   	$Release Version: 0.9 $
#   	$Revision: 1.3 $
#   	$Date: 1998/06/26 03:19:34 $
#   	by Keiju ISHITSUKA(Nihpon Rational Software Co.,Ltd.)
#     modernized by Evan Phoenix - 2011
# --
#  feature:
#  provides synchronization for multiple threads.
#
#  class methods:
#  * ThreadsWait.all_waits(thread1,...)
#    waits until all of specified threads are terminated.
#    if a block is supplied for the method, evaluates it for
#    each thread termination.
#  * th = ThreadsWait.new(thread1,...)
#    creates synchronization object, specifying thread(s) to wait.
#  
#  methods:
#  * th.threads
#    list threads to be synchronized
#  * th.empty?
#    is there any thread to be synchronized.
#  * th.finished?
#    is there already terminated thread.
#  * th.join(thread1,...) 
#    wait for specified thread(s).
#  * th.join_nowait(threa1,...)
#    specifies thread(s) to wait.  non-blocking.
#  * th.next_wait
#    waits until any of specified threads is terminated.
#  * th.all_waits
#    waits until all of specified threads are terminated.
#    if a block is supplied for the method, evaluates it for
#    each thread termination.
#

require "thread"

#
# This class watches for termination of multiple threads.  Basic functionality
# (wait until specified threads have terminated) can be accessed through the
# class method ThreadsWait::all_waits.  Finer control can be gained using
# instance methods.
#
# Example:
#
#   ThreadsWait.all_waits(thr1, thr2, ...) do |t|
#     STDERR.puts "Thread #{t} has terminated."
#   end
#
class ThreadsWait
  RCS_ID='-$Id: thwait.rb:git 1.4 2011/01/24 00:00:00 evan $-'
 
  class ErrNoWaitingThread < StandardError
  end

  class ErrNoFinishedThread < StandardError
  end

  #
  # Waits until all specified threads have terminated.  If a block is provided,
  # it is executed for each thread termination.
  #
  def ThreadsWait.all_waits(*threads) # :yield: thread
    tw = ThreadsWait.new(*threads)
    if block_given?
      tw.all_waits do |th|
        yield th
      end
    else
      tw.all_waits
    end
  end
  
  #
  # Creates a ThreadsWait object, specifying the threads to wait on.
  # Non-blocking.
  #
  def initialize(*threads)
    @threads = []
    @wait_queue = Queue.new
    join_nowait(*threads) unless threads.empty?
  end
  
  # Returns the array of threads in the wait queue.
  attr_reader :threads
  
  #
  # Returns +true+ if there are no threads to be synchronized.
  #
  def empty?
    @threads.empty?
  end
  
  #
  # Returns +true+ if any thread has terminated.
  #
  def finished?
    !@wait_queue.empty?
  end
  
  #
  # Waits for specified threads to terminate.
  #
  def join(*threads)
    join_nowait(*threads)
    next_wait
  end
  
  #
  # Specifies the threads that this object will wait for, but does not actually
  # wait.
  #
  def join_nowait(*threads)
    threads.flatten!
    @threads.concat threads

    threads.each do |th|
      Thread.start(th) do |t|
        begin
          t.join
        ensure
          @wait_queue.push t
        end
      end
    end
  end
  
  #
  # Waits until any of the specified threads has terminated, and returns the one
  # that does.
  #
  # If there are no pending threads to wait for, raises +ErrNoWaitingThread+. 
  # If +nonblock+ is true and there is no terminated thread,
  # raises +ErrNoFinishedThread+.
  #
  def next_wait(nonblock=nil)
    raise ErrNoWaitingThread, "No threads for waiting" if @threads.empty?

    begin
      th = @wait_queue.pop(nonblock)
      @threads.delete th
      return th
    rescue ThreadError
      raise ErrNoFinishedThread, "No finished threads"
    end
  end
  
  #
  # Waits until all of the specified threads are terminated.  If a block is
  # supplied for the method, it is executed for each thread termination.
  #
  # Raises exceptions in the same manner as +next_wait+.
  #
  def all_waits
    until @threads.empty?
      th = next_wait
      yield th if block_given?
    end
  end
end

# deprecated alias

ThWait = ThreadsWait

# Documentation comments:
#  - Source of documentation is evenly split between Nutshell, existing
#    comments, and my own rephrasing.
#  - I'm not particularly confident that the comments are all exactly correct.
#  - The history, etc., up the top appears in the RDoc output.  Perhaps it would
#    be better to direct that not to appear, and put something else there
#    instead.