From: tristin.colby@...
Date: 2009-02-17T06:46:23+09:00
Subject: Ruby Threading question Creating 4 threads

Newbie Question:

I have some code where I create 4 threads that pop elements off an
array and process them.  The problem is that each thread only pops off
one element, processes it, then returns; they don't continue to
process until the entire array is consumed.

<code>
$jobs = %w[a b c d e f g]
def simulate_cleanup

  puts "Checking for #{$jobs.length} jobs in /mnt/gen1/focal/temp"
  threads = []

  mu = Mutex.new
  total = 0

  1.upto(4) do |c|
     threads << Thread.new do
      puts "Thread #{c} created"
      job = nil

      mu.synchronize do
        job = $jobs.pop
        puts "Checking for #{job}"
        #Exit our thread if we have no more jobs to check
        puts "No more jobs" and return if job.nil?
      end

      t = count_files(job)
      mu.synchronize { total += t }
    end
  end
  threads.each { |t| t.join }

  puts "Reduced by #{total} files"
end

Example of output:
Thread 1 created
Thread 2 created
Thread 3 created
Thread 4 created
Checking for a
Checking for b
Checking for c
Checking for d