Fix "Event loop Closed" error

src/guidellm/backend/backend.py

@@ -110,6 +110,14 @@ def info(self) -> dict[str, Any]:
         """
         ...
 
+    @abstractmethod
+    async def reset(self) -> None:
+        """
+        Reset the connection object. This is useful for backends that
+        reuse connections or have state that needs to be cleared.
+        """
+        ...
+
     async def validate(self):
         """
         Handle final setup and validate the backend is ready for use.
@@ -126,6 +134,8 @@ async def validate(self):
         ):  # type: ignore[attr-defined]
             pass
 
+        await self.reset()
+
     @abstractmethod
     async def check_setup(self):
         """

src/guidellm/backend/openai.py

@@ -157,6 +157,15 @@ def info(self) -> dict[str, Any]:
             "chat_completions_path": CHAT_COMPLETIONS_PATH,
         }
 
+    async def reset(self) -> None:
+        """
+        Reset the connection object. This is useful for backends that
+        reuse connections or have state that needs to be cleared.
+        For this backend, it closes the async client if it exists.
+        """
+        if self._async_client is not None:
+            await self._async_client.aclose()
+
     async def check_setup(self):
         """
         Check if the backend is setup correctly and can be used for requests.
@@ -361,7 +370,7 @@ def _get_async_client(self) -> httpx.AsyncClient:
 
         :return: The async HTTP client.
         """
-        if self._async_client is None:
+        if self._async_client is None or self._async_client.is_closed:
             client = httpx.AsyncClient(
                 http2=self.http2,
                 timeout=self.timeout,

tests/unit/mock_backend.py

@@ -41,6 +41,9 @@ def model(self) -> Optional[str]:
     def info(self) -> dict[str, Any]:
         return {}
 
+    async def reset(self) -> None:
+        pass
+
     async def prepare_multiprocessing(self):
         pass