fix(service_logger): don't run an event loop for sync service events nobody receives

With no service callback configured, the sync service hooks still ran
asyncio.run() after every call. Under gevent that loop is visible to every
greenlet on the thread, and Django then rejects their database queries with
SynchronousOnlyOperation. Skip it when there is nothing to receive the event.

Fixes #43690

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

litellm/_service_logger.py

@@ -133,6 +133,16 @@ class ServiceLogging(CustomLogger):
         except Exception as e:
             verbose_logger.exception("Error emitting service event - %s", e)
 
+    def _has_service_event_observers(self) -> bool:
+        """Whether anything would receive a service event sent from a blocking caller.
+
+        Sending one runs an event loop on the calling thread. Under gevent, every
+        greenlet on that thread then sees a running loop, and Django rejects their
+        database queries with ``SynchronousOnlyOperation``. So skip it when there is
+        no service callback (or test counter) to receive the event.
+        """
+        return bool(litellm.service_callback) or self.mock_testing
+
     @staticmethod
     def _dispatch_from_sync(hook: Callable[[], Coroutine[object, object, None]]) -> None:
         """Run an async service hook from a blocking caller, whatever event loop it holds.
@@ -167,6 +177,8 @@ class ServiceLogging(CustomLogger):
 
         if self.mock_testing:
             self.mock_testing_sync_success_hook += 1
+        if not self._has_service_event_observers():
+            return
 
         self._dispatch_from_sync(
             lambda: self.async_service_success_hook(
@@ -196,6 +208,8 @@ class ServiceLogging(CustomLogger):
         """
         if self.mock_testing:
             self.mock_testing_sync_failure_hook += 1
+        if not self._has_service_event_observers():
+            return
 
         self._dispatch_from_sync(
             lambda: self.async_service_failure_hook(

tests/unit/test_service_logger.py

@@ -5,6 +5,9 @@ Regression test for KeyError: 'call_type' when async_log_success_event
 is called without call_type in kwargs (e.g. from batch polling callbacks).
 """
 
+import asyncio
+import asyncio.events
+
 import pytest
 from datetime import datetime
 from unittest.mock import AsyncMock, patch
@@ -277,3 +280,50 @@ async def test_service_failure_span_not_duplicated_for_string_and_instance(
         s for s in exporter.get_finished_spans() if s.name == "postgres get_user_object"
     ]
     assert len(db_spans) == 1
+
+
+_SYNC_HOOK_CALLS = [
+    pytest.param("service_success_hook", {}, id="success"),
+    pytest.param("service_failure_hook", {"error": RuntimeError("boom")}, id="failure"),
+]
+
+
+@pytest.fixture
+def started_loops(monkeypatch) -> list[asyncio.AbstractEventLoop]:
+    """Event loops started during the test."""
+    started: list[asyncio.AbstractEventLoop] = []
+    original = asyncio.events._set_running_loop
+
+    def recording_set_running_loop(loop):
+        if loop is not None:
+            started.append(loop)
+        original(loop)
+
+    monkeypatch.setattr(asyncio.events, "_set_running_loop", recording_set_running_loop)
+    return started
+
+
+@pytest.mark.parametrize("hook_name, extra_kwargs", _SYNC_HOOK_CALLS)
+def test_sync_service_hook_starts_no_event_loop_without_callbacks(monkeypatch, started_loops, hook_name, extra_kwargs):
+    """With no service callback, nothing receives the event, so no loop should start."""
+    monkeypatch.setattr(litellm, "service_callback", [])
+
+    getattr(ServiceLogging(), hook_name)(service=ServiceTypes.REDIS, duration=0.1, call_type="test", **extra_kwargs)
+
+    assert started_loops == []
+
+
+@pytest.mark.parametrize("hook_name, extra_kwargs", _SYNC_HOOK_CALLS)
+def test_sync_service_hook_still_delivers_to_configured_callbacks(
+    monkeypatch, started_loops, hook_name, extra_kwargs
+):
+    """With a service callback, the event is still delivered."""
+    monkeypatch.setattr(litellm, "service_callback", ["datadog"])
+    service_logger = ServiceLogging()
+    async_hook_name = f"async_{hook_name}"
+
+    with patch.object(service_logger, async_hook_name, new_callable=AsyncMock) as mock_hook:
+        getattr(service_logger, hook_name)(service=ServiceTypes.REDIS, duration=0.1, call_type="test", **extra_kwargs)
+
+    mock_hook.assert_awaited_once()
+    assert started_loops