Sample answer for thread "Threading in ruby"

sc.rb

require 'thread'

# explicit type for items that we process here
Item = Struct.new :name, :sha1, :meta

# dummies
def sha1(x) x.hash end
def update_metadata(it) it.meta = Time.now end

#
# main
#
files = [Item["f1"], Item["f2"], Item["f3"]]
queue = Queue.new

updater = Thread.new do
  until (item = queue.deq).nil?
    update_metadata(item)
    p item # debug
  end
end

# no extra thread needed
files.each do |f|
  f.sha1 = sha1(f.name)
  queue.enq f
end

# indicate termination
queue.enq nil

# graceful shutdown
updater.join

sc2.rb

require 'thread'

# explicit type for items that we process here
Item = Struct.new :name, :sha1, :meta

# dummies
def sha1(x) x.hash end
def update_metadata(it) it.meta = Time.now end

#
# main
#
files = [Item["f1"], Item["f2"], Item["f3"]]
index = -1

mutex = Mutex.new
available = ConditionVariable.new

updater = Thread.new do
  files.size.times do |i|
    mutex.synchronize do
      while i > index
        available.wait(mutex)
      end
    end

    item = files[i]
    update_metadata(item)
    p item # debug
  end
end

# no extra thread needed
files.each_with_index do |f, i|
  f.sha1 = sha1(f.name)

  mutex.synchronize do
    index = i
    available.signal
  end
end

# graceful shutdown
updater.join