[BE] [c10d][send] Improve error message on dist.send() with destinati…

…on rank as itself (#89004)

This improves error msg on dist.send() and add corresponding test in test_c10d_common.py(https://github.com/pytorch/pytorch/blob/master/test/distributed/test_c10d_common.py).
Context in issue#83912: #83912

Pull Request resolved: #89004
Approved by: https://github.com/H-Huang

test/distributed/test_c10d_common.py

@@ -1427,6 +1427,9 @@ def test_send_recv(self):
         dist.send(input_tensor, (self.rank + 1) % self.world_size)
         self.assertEqual(input_tensor, torch.zeros(2, 2) + 1)
 
+        with self.assertRaises(ValueError):
+            dist.send(input_tensor, dist.get_rank())
+
         # test recv
         input_tensor = torch.zeros(2, 2)
         dist.recv(input_tensor, (self.rank + 1) % self.world_size)

torch/distributed/distributed_c10d.py

@@ -1179,12 +1179,19 @@ def send(tensor: torch.Tensor, dst: int, group: Optional[ProcessGroup] = None, t
 
     Args:
         tensor (Tensor): Tensor to send.
-        dst (int): Destination rank.
+        dst (int): Destination rank. Destination rank should not be the same
+        as the rank of the current process.
         group (ProcessGroup, optional): The process group to work on. If None,
             the default process group will be used.
         tag (int, optional): Tag to match send with remote recv
 
     """
+    if get_rank() == dst:
+        raise ValueError(
+            "Invalid destination rank: destination rank should not be the same as "
+            "the rank of the current process."
+        )
+
     _check_single_tensor(tensor, "tensor")
     if _rank_not_in_group(group):
         _warn_not_in_group("send")