fix destroy process group error when using p2p update (#30)

Author: ruizhang1230

checkpoint_engine/ps.py

@@ -792,13 +792,15 @@ def update(
                     self.init_process_group()
                 self._update_per_bucket(checkpoint_name, req_func)
             else:
-                if self._rank not in ranks:
+                if not self._auto_pg and self._rank not in ranks:
                     return
                 if self._auto_pg:
                     if dist.is_initialized():
                         dist.destroy_process_group()
                         # HACK: wait 2s to ensure destroy is finished
                         time.sleep(2)
+                    if self._rank not in ranks:
+                        return
                     self.init_process_group_for_ranks(ranks)
                 self._update_per_bucket_p2p(checkpoint_name, req_func, ranks)
             if self._auto_pg: