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Killing worker #0
Killing worker #1
Killing worker #2
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Killing worker #4
<#0> releasing job #31
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require_relative 'equiset'

WORKER_COUNT = 5
JOB_COUNT = 10 * WORKER_COUNT
DURATION = 60

# Create and fill the pool with integer jobs
pool = EquiSet.new
(0..JOB_COUNT).each do |i|
  pool.append(i)
end

def do_work(pool, thread_id, random)
  job = pool.take
  if job
    puts "<##{thread_id}> taking job ##{job}"
    sleep_time = 0.5 + random.rand(1.5)
    sleep sleep_time
  else
    puts "<##{thread_id}> no free job, waiting a few seconds..."
    sleep 3
  end
ensure
  if job
    puts "<##{thread_id}> releasing job ##{job}"
    pool.release(job)
  end
end

# Spawn workers
workers = (0...WORKER_COUNT).map do |i|
  Thread.new do
    random = Random.new
    loop do
      do_work(pool, i, random)
    end
  end
end

# Let the program run during DURATION seconds
sleep DURATION

workers.each_with_index do |worker, i|
  puts "Killing worker ##{i}"
  worker.kill
end

require 'set'
require 'thread'

# A thread safe pool of values that can change.
class EquiSet
  def initialize
    @sorted_set = SortedSet.new
    @mutex = Monitor.new
  end

  def include?(value)
    item = Item.new(value)
    @sorted_set.include?(item)
  end

  def append(value)
    safely do
      item = Item.new(value)
      @sorted_set.add(item)
    end
  end

  # Deletes a value in the pool. Returns nil if the
  # value wasn't there and returns the value otherwise.
  def delete(value)
    safely do
      item = Item.new(value)
      item = @sorted_set.delete(item)
      item && item.value
    end
  end

  # Takes the first non-taken item if the pool.
  def take
    safely do
      # If there is a free item, it is at the begining of
      # the set because the way the set is sorted
      # see `Item#<=>`.
      item = @sorted_set.first

      if item && item.free?
        # Deletes the matching item
        @sorted_set.delete(item)

        # Adds a new but non-free item with the same value
        new_item = Item.new(item.value, free: false)
        @sorted_set.add(new_item)

        # Return the value of the matching item
        item.value
      end
    end
  end

  # Release a non-free value if it exists. It append the value
  # at the end of the pool. It returns nil if the value wasn't
  # there anymore and the value itself otherwise.
  def release(value)
    safely do
      if delete(value)
        append(value)
        value
      end
    end
  end

  def safely(&block)
    @mutex.synchronize do
      block.call
    end
  end

  # Define a class that is used by the EquiSet to sort the elements.
  # Each item is tagged with its creation date. The Item provide
  # the adequate methods to be used in a SortedSet: <=>, hash and eql?.
  class Item
    attr_reader :value
    attr_reader :key

    def initialize(value, free: true)
      @value = value
      @key = Time.now
      @free = !!free
    end

    def free?
      @free
    end

    def <=>(other)
      # Same values are the same item
      if other.value == @value
        return 0
      end

      # Free items goes first
      if other.free? != @free
        return @free ? -1 : 1
      end

      # Order by key (timestamp) otherwise
      @key <=> other.key
    end

    def hash
      @value.hash
    end

    def ==(other)
      other.value == @value
    end

    alias eql? ==
  end
end