Separation of entities from a queue

• Clone queue
  • incoming entities are duplicated and routed to a FIFO and a LIFO queue
  • jockey event → entity is taken from the LIFO queue
  • bookkeeping device destroys clones, whose partner has already left
  • 
• Result
  • complex timing problems → cumbersome and error prone
  • one needs generic solution
  • maybe similar to user chains in GPSS