fix: remove cache eviction close that kills in-use httpx clients

LLMClientCache._remove_key() was eagerly closing httpx/OpenAI clients on
cache eviction. If any in-flight request still held a reference to the
evicted client, the request failed with:

  RuntimeError: Cannot send a request, as the client has been closed.

This manifested in production after 1-2 hours (matching the 1-hour
_DEFAULT_TTL_FOR_HTTPX_CLIENTS). The fix was previously applied in PR
#22247 but regressed when commit fb72979432 re-added the close logic to
address unawaited coroutine warnings.

The correct fix is to NOT close clients on eviction at all:
- Evicted clients may still be referenced by in-flight requests
- Without calling close(), no coroutines are created, so no warnings
- Python GC handles cleanup when all references are dropped
- close_litellm_async_clients() handles explicit shutdown cleanup

Fixes the 'Cannot send a request, as the client has been closed' error
for OpenAI, Azure, and Bedrock streaming after 1+ hours of operation.

Co-authored-by: Ishaan Jaff <ishaan-jaff@users.noreply.github.com>

litellm/caching/llm_caching_handler.py

@@ -3,36 +3,21 @@ Add the event loop to the cache key, to prevent event loop closed errors.
 """
 
 import asyncio
-from typing import Set
 
 from .in_memory_cache import InMemoryCache
 
 
 class LLMClientCache(InMemoryCache):
-    # Background tasks must be stored to prevent garbage collection, which would
-    # trigger "coroutine was never awaited" warnings. See:
-    # https://docs.python.org/3/library/asyncio-task.html#creating-tasks
-    # Intentionally shared across all instances as a global task registry.
-    _background_tasks: Set[asyncio.Task] = set()
+    """Cache for LLM HTTP clients (OpenAI, Azure, httpx, etc.).
 
-    def _remove_key(self, key: str) -> None:
-        """Close async clients before evicting them to prevent connection pool leaks."""
-        value = self.cache_dict.get(key)
-        super()._remove_key(key)
-        if value is not None:
-            close_fn = getattr(value, "aclose", None) or getattr(value, "close", None)
-            if close_fn and asyncio.iscoroutinefunction(close_fn):
-                try:
-                    task = asyncio.get_running_loop().create_task(close_fn())
-                    self._background_tasks.add(task)
-                    task.add_done_callback(self._background_tasks.discard)
-                except RuntimeError:
-                    pass
-            elif close_fn and callable(close_fn):
-                try:
-                    close_fn()
-                except Exception:
-                    pass
+    IMPORTANT: This cache intentionally does NOT close clients on eviction.
+    Evicted clients may still be in use by in-flight requests. Closing them
+    eagerly causes ``RuntimeError: Cannot send a request, as the client has
+    been closed.`` errors in production after the TTL (1 hour) expires.
+
+    Clients that are no longer referenced will be garbage-collected normally.
+    For explicit shutdown cleanup, use ``close_litellm_async_clients()``.
+    """
 
     def update_cache_key_with_event_loop(self, key):
         """

tests/test_litellm/caching/test_llm_caching_handler.py

@@ -1,3 +1,13 @@
+"""
+Tests for LLMClientCache.
+
+The cache intentionally does NOT close clients on eviction because evicted
+clients may still be referenced by in-flight requests.  Closing them eagerly
+causes ``RuntimeError: Cannot send a request, as the client has been closed.``
+
+See: https://github.com/BerriAI/litellm/pull/22247
+"""
+
 import asyncio
 import os
 import sys
@@ -33,12 +43,12 @@ class MockSyncClient:
 
 
 @pytest.mark.asyncio
-async def test_remove_key_no_unawaited_coroutine_warning():
+async def test_remove_key_does_not_close_async_client():
     """
-    Test that evicting an async client from LLMClientCache does not produce
-    'coroutine was never awaited' warnings.
+    Evicting an async client from LLMClientCache must NOT close it because
+    an in-flight request may still hold a reference to the client.
 
-    Regression test for https://github.com/BerriAI/litellm/issues/22128
+    Regression test for production 'client has been closed' crashes.
     """
     cache = LLMClientCache(max_size_in_memory=2)
 
@@ -46,43 +56,19 @@ async def test_remove_key_no_unawaited_coroutine_warning():
     cache.cache_dict["test-key"] = mock_client
     cache.ttl_dict["test-key"] = 0  # expired
 
-    with warnings.catch_warnings(record=True) as caught_warnings:
-        warnings.simplefilter("always")
-        cache._remove_key("test-key")
-        # Let the event loop process the close task
-        await asyncio.sleep(0.1)
-
-    coroutine_warnings = [
-        w for w in caught_warnings if "coroutine" in str(w.message).lower()
-    ]
-    assert (
-        len(coroutine_warnings) == 0
-    ), f"Got unawaited coroutine warnings: {coroutine_warnings}"
-
-
-@pytest.mark.asyncio
-async def test_remove_key_closes_async_client():
-    """
-    Test that evicting an async client from the cache properly closes it.
-    """
-    cache = LLMClientCache(max_size_in_memory=2)
-
-    mock_client = MockAsyncClient()
-    cache.cache_dict["test-key"] = mock_client
-    cache.ttl_dict["test-key"] = 0
-
     cache._remove_key("test-key")
-    # Let the event loop process the close task
+    # Give the event loop a chance to run any background tasks
     await asyncio.sleep(0.1)
 
-    assert mock_client.closed is True
+    # Client must NOT be closed — it may still be in use
+    assert mock_client.closed is False
     assert "test-key" not in cache.cache_dict
     assert "test-key" not in cache.ttl_dict
 
 
-def test_remove_key_closes_sync_client():
+def test_remove_key_does_not_close_sync_client():
     """
-    Test that evicting a sync client from the cache properly closes it.
+    Evicting a sync client from the cache must NOT close it.
     """
     cache = LLMClientCache(max_size_in_memory=2)
 
@@ -92,15 +78,15 @@ def test_remove_key_closes_sync_client():
 
     cache._remove_key("test-key")
 
-    assert mock_client.closed is True
+    assert mock_client.closed is False
     assert "test-key" not in cache.cache_dict
 
 
 @pytest.mark.asyncio
-async def test_eviction_closes_async_clients():
+async def test_eviction_does_not_close_async_clients():
     """
-    Test that cache eviction (when cache is full) properly closes async clients
-    without producing warnings.
+    When the cache is full and an entry is evicted, the evicted async client
+    must remain open and must not produce 'coroutine was never awaited' warnings.
     """
     cache = LLMClientCache(max_size_in_memory=2, default_ttl=1)
 
@@ -123,11 +109,41 @@ async def test_eviction_closes_async_clients():
         len(coroutine_warnings) == 0
     ), f"Got unawaited coroutine warnings: {coroutine_warnings}"
 
+    # Evicted clients must NOT be closed
+    for client in clients:
+        assert client.closed is False
+
+
+@pytest.mark.asyncio
+async def test_eviction_no_unawaited_coroutine_warning():
+    """
+    Evicting an async client from LLMClientCache must not produce
+    'coroutine was never awaited' warnings.
+
+    Regression test for https://github.com/BerriAI/litellm/issues/22128
+    """
+    cache = LLMClientCache(max_size_in_memory=2)
+
+    mock_client = MockAsyncClient()
+    cache.cache_dict["test-key"] = mock_client
+    cache.ttl_dict["test-key"] = 0  # expired
+
+    with warnings.catch_warnings(record=True) as caught_warnings:
+        warnings.simplefilter("always")
+        cache._remove_key("test-key")
+        await asyncio.sleep(0.1)
+
+    coroutine_warnings = [
+        w for w in caught_warnings if "coroutine" in str(w.message).lower()
+    ]
+    assert (
+        len(coroutine_warnings) == 0
+    ), f"Got unawaited coroutine warnings: {coroutine_warnings}"
+
 
 def test_remove_key_no_event_loop():
     """
-    Test that _remove_key doesn't raise when there's no running event loop
-    (falls through to the RuntimeError except branch).
+    _remove_key works correctly even when there's no running event loop.
     """
     cache = LLMClientCache(max_size_in_memory=2)
 
@@ -140,19 +156,19 @@ def test_remove_key_no_event_loop():
     assert "test-key" not in cache.cache_dict
 
 
-@pytest.mark.asyncio
-async def test_background_tasks_cleaned_up_after_completion():
+def test_remove_key_removes_plain_values():
     """
-    Test that completed close tasks are removed from the _background_tasks set.
+    _remove_key correctly removes non-client values (strings, dicts, etc.).
     """
-    cache = LLMClientCache(max_size_in_memory=2)
+    cache = LLMClientCache(max_size_in_memory=5)
 
-    mock_client = MockAsyncClient()
-    cache.cache_dict["test-key"] = mock_client
-    cache.ttl_dict["test-key"] = 0
+    cache.cache_dict["str-key"] = "hello"
+    cache.ttl_dict["str-key"] = 0
+    cache.cache_dict["dict-key"] = {"foo": "bar"}
+    cache.ttl_dict["dict-key"] = 0
 
-    cache._remove_key("test-key")
-    # Let the task complete
-    await asyncio.sleep(0.1)
+    cache._remove_key("str-key")
+    cache._remove_key("dict-key")
 
-    assert len(cache._background_tasks) == 0
+    assert "str-key" not in cache.cache_dict
+    assert "dict-key" not in cache.cache_dict