def pop_connection(self, identifier):
        self.global_max.acquire()
        try:
            self.lock.acquire()
            if identifier not in self.clists:
                self.clists[identifier] = ConnectionList(self.max_connections_per_host)
            clist = self.clists[identifier]
            self.lock.release()
            if not clist.max.acquire(false): # acquire local lock, releasing global lock when waiting
                self.global_max.release()
                clist.max.acquire()
                self.global_max.acquire()
            try:
                # we hebben nu zowel toestemming voor een global als voor een local connection
                # kijk eerst of er zo'n verbinding bestaat
                self.lock.acquire()
                try:
                    if len(clist) > 0:
                        connection = clist.pop()
                    else:
                        # pop the oldest connection from the connection stack
                        old_connection = self.connections.pop(0)
                        for clist in self.ids:
                            if old_connection in clist:
                                clist.remove(old_connection)
                                break # a connection is in max one clist
                        connection = None # signal we need a new connection
                finally:
                    self.lock.release()
            except:
                clist.max.release()            
                raise
        except:
            clist.max.release()
            raise