From: Oliver Cat <apple.hater+ruby@...>
Date: 2010-04-28T20:39:16+09:00
Subject: Mutex

Hi all,
I've been reading the RailsDispatch blog, and have been looking at this
code.

class BlacklistConstraint
  def initialize
    @ips = Blacklist.retrieve_ips
    @mutex = Mutex.new
    @last_update = Time.now
  end

  def matches?(request)
    @mutex.synchronize do
      if (Time.now - @last_update) > 3600
        @ips = Blacklist.retrieve_ips
        @last_update = Time.now
      end
    end

    !@ips.include?(request.remote_ip)
  end
end

What interests me is the 'matches?' method, specifically the
mutex.synchronize block. I'm wondering what is the benefit of this code,
and how it works?

Is it so other attempts to call Blacklist.retrieve_ips are blocked, and
if so, should the mutex be implemented in the Blacklist class?

thanks for reading.
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