From: Tom Felker <tcfelker@...>
Date: 2003-06-02T14:34:13+09:00
Subject: Re: thread-unsafe stuff: could you summarize?

While you're asking that, I have a similar question: is the following
thread-safe?  (This is part of PeerTalk, a LAN chat program I'm
writing.)

-----
=begin
defer.rb - the Defer module

Defer is used to defer the execution of a block of code, to simplify
multi-threaded programming.  Defer is useful when a GUI thread must be
the only thread that interacts with the toolkit, but other threads may
make demands on the GUI at any time.  Defer can be mixed in to the GUI
class.

To defer a block, call defer with the block.  This can be done from
any thread, and defer will return immediately.  When you are ready to
run the blocks, call run_deferred, which will execute the blocks in
the context of the calling thread (not the thread which defered them).
If a deferred block defers a block, that block will be executed
immediately, and the callback won't be called.

To be notified when a block is deferred, call set_defer_callback with
an associated block.  This block will be called whenever a block is
deferred, in the context of the thread defering it.  You can use this
to notify the GUI thread that calling run_deferred is necessary.

=end

require "thread"

module Defer

  def initialize
    super
    @deferBlocks = Queue.new
    @deferRunning = false
    @deferCallback = Proc.new { }
    @deferMutex = Mutex.new
  end

  def defer
    if @deferRunning
      yield
    else
      @deferBlocks.push Proc.new
      @deferCallback.call
    end
  end

  def run_deferred
    return if @deferRunning
    @deferMutex.synchronize do
      @deferRunning = true
      begin
        until @deferBlocks.empty?
          @deferBlocks.pop.call
        end
      ensure
        @deferRunning = false
      end
    end
  end

  def set_defer_callback
    @deferCallback = Proc.new
  end

end

class Deferrer
  include Defer
  def initialize(*args)
    super(*args)
  end
end




-- 
Tom Felker

If we developed a replicator, it would be banned for its threat to
the profits of existing business.