Prioritized work queue with weighted items

output.txt

#
# statistics
#

#<WorkQueue:0x10039da4
 @p=#<Proc:0x10032734>,
 @q=
  [#<Picker:0x10039d7c
    @items=[#<struct SRV domain="server-1", port=1234, priority=1, weight=1>],
    @total=1,
    @weight=#<Proc:0x1003293c>>,
   #<Picker:0x10039d54
    @items=
     [#<struct SRV domain="server-2-A", port=1234, priority=2, weight=16>,
      #<struct SRV domain="server-2-B", port=1234, priority=2, weight=4>,
      #<struct SRV domain="server-2-C", port=1234, priority=2, weight=8>],
    @total=28,
    @weight=#<Proc:0x1003293c>>,
   #<Picker:0x10039d2c
    @items=[#<struct SRV domain="server-3", port=1234, priority=4, weight=50>],
    @total=50,
    @weight=#<Proc:0x1003293c>>],
 @w=#<Proc:0x1003293c>>
server-1       :     100000          0          0          0          0
server-2-A     :          0      57137      32571      10292          0
server-2-B     :          0      14247      24788      60965          0
server-2-C     :          0      28616      42641      28743          0
server-3       :          0          0          0          0     100000

srv.rb

# Picks any of given items based on weight
class Picker
  def initialize(items = nil, &weight)
    @total = 0
    @items = []
    @weight = weight
    items.each {|it| self << it} if items
  end

  def empty?
    @total == 0
  end

  # add an item
  def <<(it)
    @total += @weight[it]
    @items << it
    self
  end

  # pick and leave in place
  def pick
    @items[pos]
  end

  # pick and remove
  def fetch
    it = @items.delete_at pos
    @total -= @weight[it]
    it
  end

  def dup
    super.tap do |c|
      c.instance_variable_set '@items', @items.dup
    end
  end

  def freeze
    @items.freeze
    super
  end

private

  # determine position
  def pos
    return nil if @total == 0

    sum = 0
    pick = rand(@total)

    @items.each_with_index do |it, idx|
      sum += @weight[it]
      return idx if sum > pick
    end

    raise "Algorithm error"
  end
end

# Queue of items with priorities and weights
class WorkQueue
  def initialize(items, weight, prio)
    @q = []
    @w = weight.to_proc
    @p = prio.to_proc

    items.each do |it|
      (@q[@p[it]] ||= Picker.new(&weight)) << it
    end

    @q.compact!
  end

  def empty?
    @q.all? &:empty
  end

  def deq
    until @q.empty?
      hd = @q.first

      if hd.empty?
        @q.shift
      else
        return hd.fetch
      end
    end

    nil
  end

  def freeze
    @q.each(&:freeze).freeze
    super
  end

  def dup
    super.tap do |c|
      c.instance_variable_set '@q', @q.map(&:dup)
    end
  end
end

require 'pp'

# dummy record type
SRV = Struct.new :domain, :port, :priority, :weight

# dummy connection method with log output
def connect(it)
  # simulate 1/3 is OK
  (rand(3) == 0).tap do |ok|
    printf "try %p... -> %s\n", it, ok ? "OK" : "fail"
  end
end

# dummy data
records = (1..10).map {|i| SRV.new "www#{i}.dom.com", 1000 + i, rand(3), rand(100) }

# can be reused:
template = WorkQueue.new(records, :weight, :priority).freeze
pp template

# per connection attempt
wk = template.dup

it = nil

begin
  it = wk.deq
end until it.nil? || connect(it)

pp it, wk

puts <<STR

#
# statistics
#

STR

records = [
  SRV["server-1", 1234, 1, 1],
  SRV["server-2-A", 1234, 2, 16],
  SRV["server-2-B", 1234, 2, 4],
  SRV["server-2-C", 1234, 2, 8],
  SRV["server-3", 1234, 4, 50],
]

template = WorkQueue.new(records, :weight, :priority).freeze

pp template

stats = Hash.new {|h,k| h[k] = Array.new(records.length, 0)}

100_000.times do
  wk = template.dup
  pos = 0

  while it = wk.deq
    stats[it.domain][pos] += 1
    pos += 1
  end

end

stats.sort.each do |srv, positions|
  printf "%-15s: %s\n", srv, positions.map {|count| "%10d" % count}.join(' ')
end