[EPLB] Add alternative communication for EPLB weight exchange (#33176)

Signed-off-by: ilmarkov <markovilya197@gmail.com>
Signed-off-by: Markov Ilya <markovilya19@gmail.com>
Co-authored-by: Markov Ilya <markovilya19@gmail.com>

tests/distributed/eplb_utils.py

@@ -1,9 +1,11 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
+import atexit
 import os
 import random
 
+import pytest
 import torch
 import torch.multiprocessing as mp
 
@@ -16,9 +18,20 @@ from vllm.utils.system_utils import update_environment_variables
 mp.set_start_method("spawn", force=True)
 
 
+def _distributed_worker_wrapper(fn, env, world_size, args, rank, skip_queue):
+    try:
+        fn(env, world_size, *args)
+    except BaseException as exc:
+        if isinstance(exc, pytest.skip.Exception):
+            skip_queue.put((rank, str(exc)))
+            return
+        raise
+
+
 def distributed_run(fn, world_size, *args):
     number_of_processes = world_size
     processes: list[mp.Process] = []
+    skip_queue: mp.SimpleQueue = mp.SimpleQueue()
     for i in range(number_of_processes):
         env: dict[str, str] = {}
         env["RANK"] = str(i)
@@ -27,13 +40,32 @@ def distributed_run(fn, world_size, *args):
         env["LOCAL_WORLD_SIZE"] = str(number_of_processes)
         env["MASTER_ADDR"] = "localhost"
         env["MASTER_PORT"] = "12345"
-        p = mp.Process(target=fn, args=(env, world_size, *args))
+        p = mp.Process(
+            target=_distributed_worker_wrapper,
+            args=(fn, env, world_size, args, i, skip_queue),
+        )
         processes.append(p)
         p.start()
 
     for p in processes:
         p.join()
 
+    skipped: list[tuple[int, str]] = []
+    while not skip_queue.empty():
+        rank, reason = skip_queue.get()
+        skipped.append((rank, reason))
+
+    if len(skipped) == number_of_processes:
+        reason = skipped[0][1]
+        pytest.skip(reason)
+    if 0 < len(skipped) < number_of_processes:
+        skipped_ranks = sorted(rank for rank, _ in skipped)
+        raise AssertionError(
+            "Distributed test had partial skips; expected either all ranks "
+            f"to skip or none. Skipped ranks: {skipped_ranks}, "
+            f"total ranks: {number_of_processes}"
+        )
+
     for p in processes:
         assert p.exitcode == 0
 
@@ -48,7 +80,12 @@ def set_env_vars_and_device(env: dict[str, str]) -> None:
     vllm_config = VllmConfig()
     with set_current_vllm_config(vllm_config):
         init_distributed_environment()
-
+    atexit.register(_destroy_process_group_if_initialized)
     # Ensure each worker process has the same random seed
     random.seed(42)
     torch.manual_seed(42)
+
+
+def _destroy_process_group_if_initialized() -> None:
+    if torch.distributed.is_available() and torch.distributed.is_initialized():
+        torch.distributed.destroy_process_group()