[Feat][Executor] Introduce RayExecutorV2 (#36836)

Signed-off-by: Jeffrey Wang <jeffreywang@anyscale.com>

tests/distributed/conftest.py

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import os
 import random
 
 import msgspec
@@ -166,3 +167,31 @@ class MockSubscriber:
         self.sub.close()
         for replay in self.replay_sockets:
             replay.close()
+
+
+@pytest.fixture
+def enable_ray_v2_backend():
+    """Set env vars for the Ray V2 executor backend and shut down Ray
+    between tests."""
+    import ray
+
+    saved = {
+        "VLLM_USE_RAY_V2_EXECUTOR_BACKEND": os.environ.get(
+            "VLLM_USE_RAY_V2_EXECUTOR_BACKEND"
+        ),
+        "VLLM_ENABLE_V1_MULTIPROCESSING": os.environ.get(
+            "VLLM_ENABLE_V1_MULTIPROCESSING"
+        ),
+    }
+    os.environ["VLLM_USE_RAY_V2_EXECUTOR_BACKEND"] = "1"
+    os.environ["VLLM_ENABLE_V1_MULTIPROCESSING"] = "0"
+    if ray.is_initialized():
+        ray.shutdown()
+    try:
+        yield
+    finally:
+        if ray.is_initialized():
+            ray.shutdown()
+        os.environ.update({k: v for k, v in saved.items() if v is not None})
+        for key in (k for k, v in saved.items() if v is None):
+            os.environ.pop(key, None)