global CS
  op CSenter(int id) {call}    # must be called
  op CSexit()                  # may be invoked by call or send
  int numusers = 5
  int rounds = 5
body CS
  process arbitrator  {
    for [ i = 1 to numusers * rounds ] {
      in CSenter(id) by id ->
	  write("user", id, "in its CS")
      ni
      receive CSexit()
    }
  }
end

resource main()
  import CS

  process user [ i = 1 to numusers ] {
    for [ j = 1 to rounds ] {
      call CSenter(i)
      nap(int(random()*100))
      send CSexit()
      nap(int(random()*1000))
    }
  }
end