From: Suraj Kurapati <sunaku@...>
Date: 2010-06-06T14:29:15+09:00
Subject: threads & mutex question (Rubyist book example)

Hi,

I am concerned about the lack of mutual exlusion in code listing
14.2 "Chat server using TCPServer and threads" on page 430 in "The
Well-Grounded Rubyist" book.  That code goes something like this:

  chatters = []

  while ...
    Thread.new(...) do |c|
      chatters.each { ... }
      chatters.push c
      chatters.each { ... }
      chatters.delete c
      chatters.each { ... }
    end
  end

Multiple threads are spawned and each of them accesses the shared
resource (the chatters array) directly without mutual exclusion.

What happens when a thread inside chatters.each() gets descheduled
and another thread proceeds to add or delete an object to chatters?

Shouldn't there be a Mutex#synchronize call wrapping all access to
the chatters array?

Thanks for your consideration.
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