code: def _gpu_buffer(self, idx):
      if self._gpu_buffers[idx] is None:
          self._gpu_buffers[idx] = paddle.empty(
              shape=[self.buffer_size, self.emb_dim], dtype="float32"
          )
      return self._gpu_buffers[idx]
  
imports: import numpy
  import paddle
  from paddle.framework import core
  from paddle.device import cuda
  from pgl.utils.logger import log
label_desc: Use image node_id 5 for calling the StreamPool obj's underlying member method code with example usage: obj._gpu_buffer(idx) and returns: self