code: def release_pool(self):
          
          if self._current_acquired > 0:
              raise PoolException("Can't release pool: %d connection(s) still acquired" % self._current_acquired)
          while not self._pool.empty():
              conn = self.acquire()
              conn.close()
          if self._cleanup_thread is not None:
              self._thread_event.set()
              self._cleanup_thread.join()
          self._pool = None
docs: Release pool and all its connection