[CI] Fix race condition in test_kv_cache_events test (#18169)

Signed-off-by: Russell Bryant <rbryant@redhat.com>

Author: russellb

tests/v1/engine/test_engine_core_client.py

@@ -292,7 +292,6 @@ def test_kv_cache_events(
             log_stats=False,
         )
         endpoint = publisher_config.endpoint.replace("*", "127.0.0.1")
-        time.sleep(0.1)
         subscriber = MockSubscriber(endpoint,
                                     topic=publisher_config.topic,
                                     decode_type=KVEventBatch)

vllm/distributed/kv_events.py

@@ -130,6 +130,7 @@ def __init__(
         self._endpoint = endpoint
         self._replay_endpoint = replay_endpoint
         self._hwm = hwm
+        self._socket_setup()
 
         # Payload
         self._seq_gen = count()
@@ -207,7 +208,6 @@ def _socket_setup(self) -> None:
     def _publisher_thread(self) -> None:
         """Background thread that processes the event queue."""
         self._pack = msgspec.msgpack.Encoder()
-        self._socket_setup()
 
         assert self._pub is not None  # narrows type for mypy