Playing around with id generation inspired by gosnow. And by "inspired by" I mean "a blatant copy of".

gosnow.rb

require 'zlib'
require 'socket'
require 'thread'

WORKERID_BITS = 10 
MAX_WORKER_ID = -1 ^ (-1 << WORKERID_BITS)
SEQUENCE_BITS = 12
MAX_SEQUENCE = -1 ^ (-1 << SEQUENCE_BITS)

SINCE_MILLIS = Time.utc(2012, 1, 1).to_f * 1000

class SnowFlake

  def initialize worker_id = self.default_worker_id
    fail "Invalid worker id" if (worker_id < 0 || worker_id > MAX_WORKER_ID)
    self.worker_id = worker_id
    self.last_timestamp = 0
    self.sequence = 0
    self.lock = Mutex.new
  end

  def next
      ts = timestamp
      if ts == last_timestamp
        self.sequence = (sequence+1) & MAX_SEQUENCE
        if sequence == 0
          ts = til_next_millis(ts)
        end
      else
        self.sequence = 0
      end

      fail "Invalid timestamp, #{ts} preceeds #{self}" if ts < last_timestamp
      self.last_timestamp = ts

      as_int64
  end

  def as_int64
    (last_timestamp << (WORKERID_BITS + SEQUENCE_BITS)) |
      (worker_id << SEQUENCE_BITS) |
      sequence
  end

  def timestamp
    (Time.now.to_f * 1000).to_i
  end

  def til_next_millis ts
    i = timestamp
    while i < ts
      sleep 0.0001
      i = timestamp
    end
    i
  end

  def default_worker_id
    id = Zlib.crc32 [Socket.gethostname, Process.pid.to_s].join(":") 
    MAX_WORKER_ID & id
  end

  attr_accessor :last_timestamp, :worker_id, :sequence, :lock
end


sf = SnowFlake.new
1000_000.times { 
  val = sf.next
  c = [val >> 32, val & 0xFFFFFFFF].pack("NN")
  b = [val].pack("w")
  puts [c].pack("m").delete('='), [b].pack("m").delete('=')
}