Add support for async method and remove context PythonServer (#16453)

Co-authored-by: thomas <thomas@thomass-MacBook-Pro.local>

src/lightning_app/CHANGELOG.md

@@ -14,7 +14,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Changed
 
--
+- Add support for async predict method in PythonServer and remove torch context ([#16453](https://github.com/Lightning-AI/lightning/pull/16453))
 
 
 ### Deprecated

src/lightning_app/components/serve/python_server.py

@@ -1,4 +1,5 @@
 import abc
+import asyncio
 import base64
 import os
 import platform
@@ -252,19 +253,19 @@ class PythonServer(LightningWork, abc.ABC):
         return out
 
     def _attach_predict_fn(self, fastapi_app: FastAPI) -> None:
-        from torch import inference_mode, no_grad
-
         input_type: type = self.configure_input_type()
         output_type: type = self.configure_output_type()
 
-        device = _get_device()
-        context = no_grad if device.type == "mps" else inference_mode
+        def predict_fn_sync(request: input_type):  # type: ignore
+            return self.predict(request)
 
-        def predict_fn(request: input_type):  # type: ignore
-            with context():
-                return self.predict(request)
+        async def async_predict_fn(request: input_type):  # type: ignore
+            return await self.predict(request)
 
-        fastapi_app.post("/predict", response_model=output_type)(predict_fn)
+        if asyncio.iscoroutinefunction(self.predict):
+            fastapi_app.post("/predict", response_model=output_type)(async_predict_fn)
+        else:
+            fastapi_app.post("/predict", response_model=output_type)(predict_fn_sync)
 
     def get_code_sample(self, url: str) -> Optional[str]:
         input_type: Any = self.configure_input_type()