Fail fast when LitAPI.setup has error

src/litserve/loops.py

@@ -26,7 +26,7 @@
 from litserve import LitAPI
 from litserve.callbacks import CallbackRunner, EventTypes
 from litserve.specs.base import LitSpec
-from litserve.utils import LitAPIStatus, PickleableHTTPException
+from litserve.utils import LitAPIStatus, PickleableHTTPException, WorkerSetupStatus
 
 mp.allow_connection_pickling()
 
@@ -399,18 +399,23 @@ def inference_worker(
     max_batch_size: int,
     batch_timeout: float,
     stream: bool,
-    workers_setup_status: Dict[str, bool],
+    workers_setup_status: Dict[int, str],
     callback_runner: CallbackRunner,
 ):
     callback_runner.trigger_event(EventTypes.BEFORE_SETUP, lit_api=lit_api)
-    lit_api.setup(device)
+    try:
+        lit_api.setup(device)
+    except Exception:
+        logger.exception(f"Error setting up worker {worker_id}.")
+        workers_setup_status[worker_id] = WorkerSetupStatus.ERROR
+        return
     lit_api.device = device
     callback_runner.trigger_event(EventTypes.AFTER_SETUP, lit_api=lit_api)
 
-    print(f"Setup complete for worker {worker_id}.")
+    logger.info(f"Setup complete for worker {worker_id}.")
 
     if workers_setup_status:
-        workers_setup_status[worker_id] = True
+        workers_setup_status[worker_id] = WorkerSetupStatus.READY
 
     if lit_spec:
         logging.info(f"LitServe will use {lit_spec.__class__.__name__} spec")

src/litserve/server.py

@@ -44,18 +44,10 @@
 from litserve.python_client import client_template
 from litserve.specs import OpenAISpec
 from litserve.specs.base import LitSpec
-from litserve.utils import LitAPIStatus, call_after_stream
+from litserve.utils import LitAPIStatus, WorkerSetupStatus, call_after_stream
 
 mp.allow_connection_pickling()
 
-try:
-    import uvloop
-
-    asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
-
-except ImportError:
-    print("uvloop is not installed. Falling back to the default asyncio event loop.")
-
 logger = logging.getLogger(__name__)
 
 # if defined, it will require clients to auth with X-API-Key in the header
@@ -233,7 +225,7 @@ def launch_inference_worker(self, num_uvicorn_servers: int):
             if len(device) == 1:
                 device = device[0]
 
-            self.workers_setup_status[worker_id] = False
+            self.workers_setup_status[worker_id] = WorkerSetupStatus.STARTING
 
             ctx = mp.get_context("spawn")
             process = ctx.Process(
@@ -328,7 +320,7 @@ async def index(request: Request) -> Response:
         async def health(request: Request) -> Response:
             nonlocal workers_ready
             if not workers_ready:
-                workers_ready = all(self.workers_setup_status.values())
+                workers_ready = all(v == WorkerSetupStatus.READY for v in self.workers_setup_status.values())
 
             if workers_ready:
                 return Response(content="ok", status_code=200)
@@ -436,6 +428,13 @@ def generate_client_file(port: Union[str, int] = 8000):
         except Exception as e:
             logger.exception(f"Error copying file: {e}")
 
+    def verify_worker_status(self):
+        while not any(v == WorkerSetupStatus.READY for v in self.workers_setup_status.values()):
+            if any(v == WorkerSetupStatus.ERROR for v in self.workers_setup_status.values()):
+                raise RuntimeError("One or more workers failed to start. Shutting down LitServe")
+            time.sleep(0.05)
+        logger.debug("One or more workers are ready to serve requests")
+
     def run(
         self,
         host: str = "0.0.0.0",
@@ -481,6 +480,7 @@ def run(
 
         manager, litserve_workers = self.launch_inference_worker(num_api_servers)
 
+        self.verify_worker_status()
         try:
             servers = self._start_server(port, num_api_servers, log_level, sockets, api_server_worker_type, **kwargs)
             print(f"Swagger UI is available at http://0.0.0.0:{port}/docs")

src/litserve/utils.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import asyncio
+import dataclasses
 import logging
 import pickle
 from contextlib import contextmanager
@@ -78,3 +79,11 @@ async def call_after_stream(streamer: AsyncIterator, callback, *args, **kwargs):
         logger.exception(f"Error in streamer: {e}")
     finally:
         callback(*args, **kwargs)
+
+
+@dataclasses.dataclass
+class WorkerSetupStatus:
+    STARTING: str = "starting"
+    READY: str = "ready"
+    ERROR: str = "error"
+    FINISHED: str = "finished"

tests/test_lit_server.py

@@ -213,6 +213,7 @@ def test_start_server(mock_uvicon):
 def test_server_run_with_api_server_worker_type(mock_uvicorn):
     api = ls.test_examples.SimpleLitAPI()
     server = ls.LitServer(api, devices=1)
+    server.verify_worker_status = MagicMock()
     with pytest.raises(ValueError, match=r"Must be 'process' or 'thread'"):
         server.run(api_server_worker_type="invalid")
 
@@ -247,6 +248,7 @@ def test_server_run_with_api_server_worker_type(mock_uvicorn):
 def test_server_run_windows(mock_uvicorn):
     api = ls.test_examples.SimpleLitAPI()
     server = ls.LitServer(api)
+    server.verify_worker_status = MagicMock()
     server.launch_inference_worker = MagicMock(return_value=[MagicMock(), [MagicMock()]])
     server._start_server = MagicMock()
 
@@ -258,6 +260,7 @@ def test_server_run_windows(mock_uvicorn):
 
 def test_server_terminate():
     server = LitServer(SimpleLitAPI())
+    server.verify_worker_status = MagicMock()
     mock_manager = MagicMock()
 
     with patch("litserve.server.LitServer._start_server", side_effect=Exception("mocked error")) as mock_start, patch(
@@ -392,3 +395,15 @@ def test_generate_client_file(tmp_path, monkeypatch):
     LitServer.generate_client_file(8000)
     with open(tmp_path / "client.py") as fr:
         assert expected in fr.read(), "Shouldn't replace existing client.py"
+
+
+class FailFastAPI(ls.test_examples.SimpleLitAPI):
+    def setup(self, device):
+        raise ValueError("setup failed")
+
+
+def test_workers_setup_status():
+    api = FailFastAPI()
+    server = LitServer(api, devices=1)
+    with pytest.raises(RuntimeError, match="One or more workers failed to start. Shutting down LitServe"):
+        server.run()