docstr: Destroy the group and release NCCL communicators.
docstr_tok: ["Destroy","the","group","and","release","NCCL","communicators","."]
code: def destroy_group(self):
      """Destroy the group and release NCCL communicators."""
      if len(self._dev_comm_map.keys()) > 0:
          # TODO(Hao): check this barrier call
          # self.barrier()
  
          # Destroy the communicators and streams.
          for comm_key, comms in self._dev_comm_map.items():
              for c in comms:
                  c.destroy()
              self._dev_comm_map[comm_key] = None
  
      if self.rank == 0:
          for comm_key in self._dev_comm_map:
              assert not self._dev_comm_map[comm_key]
              group_key = self._generate_group_key(comm_key)
              self._destroy_store(group_key)
      self._barrier_tensor = None
      self._dev_comm_map = None
      self._dev_streams_map = None
      super(NCCLGroup, self).destroy_group()
  
imports: import logging
  import datetime
  import time
  import ray
  import cupy
  from ray.util.collective.const import ENV
  from ray.util.collective.collective_group import nccl_util
  from ray.util.collective.collective_group.base_collective_group import BaseGroup
  from ray.util.collective.const import get_store_name
  from ray.util.collective.types import AllReduceOptions, BarrierOptions, Backend, ReduceOptions, BroadcastOptions, AllGatherOptions, ReduceScatterOptions, SendOptions, RecvOptions
  from ray.util.collective.collective_group.cuda_stream import get_stream_pool
label_desc: Use image node_id 2 for calling the NCCLGroup obj's underlying member method code with example usage: obj.destroy_group() without return types