[Bugfix][core] replace heartbeat with pid check (#9818)

Signed-off-by: Joe Runde <Joseph.Runde@ibm.com>

vllm/entrypoints/openai/api_server.py

@@ -176,13 +176,16 @@ async def build_async_engine_client_from_engine_args(
                                                UsageContext.OPENAI_API_SERVER,
                                                ipc_path))
         engine_process.start()
-        logger.info("Started engine process with PID %d", engine_process.pid)
+        engine_pid = engine_process.pid
+        assert engine_pid is not None, "Engine process failed to start"
+        logger.info("Started engine process with PID %d", engine_pid)
 
         # Build RPCClient, which conforms to EngineClient Protocol.
         # NOTE: Actually, this is not true yet. We still need to support
         # embedding models via RPC (see TODO above)
         engine_config = engine_args.create_engine_config()
-        mp_engine_client = MQLLMEngineClient(ipc_path, engine_config)
+        mp_engine_client = MQLLMEngineClient(ipc_path, engine_config,
+                                             engine_pid)
 
         try:
             while True: