Use current device id in dist.barrier

Summary:
Pull Request resolved: https://github.com/facebookresearch/detectron2/pull/3350

`get_local_rank` relies on a global variable set by Detectron2's `launch` utils.
Since other frameworks might use Detectron2's distribute utils but don't launch with Detectron2's `launch` utils. Use `torch.cuda.current_device` to get the current device instead.

Reviewed By: HarounH, ppwwyyxx

Differential Revision: D30233746

fbshipit-source-id: 0b140ed5c1e7cd87ccf05235127f338ffc40a53d

d2go/distributed.py

@@ -148,12 +148,12 @@ def _distributed_worker(
         if i == machine_rank:
             comm._LOCAL_PROCESS_GROUP = pg
 
+    if backend in ["NCCL"]:
+        torch.cuda.set_device(local_rank)
     # synchronize is needed here to prevent a possible timeout after calling
     # init_process_group
     # See: https://github.com/facebookresearch/maskrcnn-benchmark/issues/172
     comm.synchronize()
-    if backend in ["NCCL"]:
-        torch.cuda.set_device(local_rank)
 
 
     ret = main_func(*args)