From: Sriram Varahan <sriram.varahan@...>
Date: 2010-03-18T19:19:42+09:00
Subject: Thread pool issue

Hello,


     I was just trying out the thread pool code form Ruby Cookbook.

I created a script to test it out. The complete code is as follows:
-----------------------------------------------------------------------------
require 'thread'

class ThreadPool
  def initialize(max_size)
    @pool       = []
    @max_size   = max_size
    @pool_mutex = Mutex.new
    @pool_cv    = ConditionVariable.new
  end

  def dispatch(*args)
    Thread.new do
      # Wait for space in the pool.
      @pool_mutex.synchronize do
        while @pool.size >= @max_size
          puts "Pool is full; waiting to run #{args.join(',')}…\n"
          # Sleep until some other thread calls @pool_cv.signal.
          @pool_cv.wait(@pool_mutex)
        end
      end
      @pool << Thread.current
      begin
        yield(*args)
      rescue => e
        exception(self, e, *args)
      ensure
        @pool_mutex.synchronize do
          # Remove the thread from the pool.
          @pool.delete(Thread.current)
          # Signal the next waiting thread that there's a space in the
pool.
          @pool_cv.signal
        end
      end
    end
  end

  def shutdown
    @pool_mutex.synchronize { @pool_cv.wait(@pool_mutex) until
@pool.empty? }
  end

  def exception(thread, exception, *original_args)
    # Subclass this method to handle an exception within a thread.
    puts "Exception in thread #{thread}: #{exception}"
  end
end

@work = []
def no_work_only_sleep
  sleep(2)
  @work << "Finished"
end

pool = ThreadPool.new(3)

10.times do |i|
  pool.dispatch(i) do
    puts "Job #{i} started"
    no_work_only_sleep
  end
end

pool.shutdown
puts @work.length

-------------------------------------------------------------------------
What I am doing here is creating 10 jobs and within a job calling a
method.
Inside the method I am inserting a string "Finished" to an array @work.
So for 10 jobs this array should contain 10 such strings.

The issue I have here is : For a thread pool of size 3 it gives an
output of 9 where it should have been 10.

For any other thread pool value it gives 10 as required.

Any reason as to why this is happening?

Thanks,
Sriram.
-- 
Posted via http://www.ruby-forum.com/.