From: "James M. Lawrence" <quixoticsycophant@...>
Date: 2009-03-09T13:18:32+09:00
Subject: Re: 1.9.x Thread problem


Here is a bare solution using a mutex and a counter.  The next thing
would be to use a condition variable to put the main thread to sleep
while the child threads initialize, rather than spinning wheels /
burning rubber while waiting.

Also look into monitor.rb, sync.rb, and producer/consumer strategies.

require 'thread'
THREADS = 10

parent_id = Thread.current.object_id

mutex = Mutex.new
num_threads_ready = 0

queue = Queue.new
THREADS.times do |i|
   queue << Thread.new do
      th = Thread.current
      th[:index] = i
      mutex.synchronize { num_threads_ready += 1 }  # <-----
      raise "Running inside parent" if th.object_id == parent_id
      sleep(2)
   end
end

# wait until threads have initialized
until mutex.synchronize { num_threads_ready == THREADS }
   Thread.pass
end

THREADS.times do
   th = queue.pop
   raise "Running inside parent" if th.object_id == parent_id
   puts "Joining thread #{th[:index]}"
   th.join()
end
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