Revert "Expire session storage cache on an async timer (streamlit#8083)…

…" (streamlit#8281)

## Describe your changes

This reverts commit 44227ad.

---

**Contribution License Agreement**

By submitting this pull request you agree that all contributions to this
project are made under the Apache 2.0 license.

lib/streamlit/runtime/caching/cache_resource_api.py

@@ -22,6 +22,7 @@
 from datetime import timedelta
 from typing import Any, Callable, Final, TypeVar, cast, overload
 
+from cachetools import TTLCache
 from typing_extensions import TypeAlias
 
 import streamlit as st
@@ -47,7 +48,6 @@
 from streamlit.runtime.metrics_util import gather_metrics
 from streamlit.runtime.scriptrunner.script_run_context import get_script_run_ctx
 from streamlit.runtime.stats import CacheStat, CacheStatsProvider, group_stats
-from streamlit.util import TimedCleanupCache
 
 _LOGGER: Final = get_logger(__name__)
 
@@ -472,7 +472,7 @@ def __init__(
         super().__init__()
         self.key = key
         self.display_name = display_name
-        self._mem_cache: TimedCleanupCache[str, MultiCacheResults] = TimedCleanupCache(
+        self._mem_cache: TTLCache[str, MultiCacheResults] = TTLCache(
             maxsize=max_entries, ttl=ttl_seconds, timer=cache_utils.TTLCACHE_TIMER
         )
         self._mem_cache_lock = threading.Lock()

lib/streamlit/runtime/caching/storage/in_memory_cache_storage_wrapper.py

@@ -16,6 +16,8 @@
 import math
 import threading
 
+from cachetools import TTLCache
+
 from streamlit.logger import get_logger
 from streamlit.runtime.caching import cache_utils
 from streamlit.runtime.caching.storage.cache_storage_protocol import (
@@ -24,7 +26,6 @@
     CacheStorageKeyNotFoundError,
 )
 from streamlit.runtime.stats import CacheStat
-from streamlit.util import TimedCleanupCache
 
 _LOGGER = get_logger(__name__)
 
@@ -61,7 +62,7 @@ def __init__(self, persist_storage: CacheStorage, context: CacheStorageContext):
         self.function_display_name = context.function_display_name
         self._ttl_seconds = context.ttl_seconds
         self._max_entries = context.max_entries
-        self._mem_cache: TimedCleanupCache[str, bytes] = TimedCleanupCache(
+        self._mem_cache: TTLCache[str, bytes] = TTLCache(
             maxsize=self.max_entries,
             ttl=self.ttl_seconds,
             timer=cache_utils.TTLCACHE_TIMER,

lib/streamlit/runtime/memory_session_storage.py

@@ -16,8 +16,9 @@
 
 from typing import MutableMapping
 
+from cachetools import TTLCache
+
 from streamlit.runtime.session_manager import SessionInfo, SessionStorage
-from streamlit.util import TimedCleanupCache
 
 
 class MemorySessionStorage(SessionStorage):
@@ -56,7 +57,7 @@ def __init__(
             inaccessible and will be removed eventually.
         """
 
-        self._cache: MutableMapping[str, SessionInfo] = TimedCleanupCache(
+        self._cache: MutableMapping[str, SessionInfo] = TTLCache(
             maxsize=maxsize, ttl=ttl_seconds
         )
 

lib/streamlit/util.py

@@ -16,16 +16,13 @@
 
 from __future__ import annotations
 
-import asyncio
 import dataclasses
 import functools
 import hashlib
 import os
 import subprocess
 import sys
-from typing import Any, Callable, Final, Generic, Iterable, Mapping, TypeVar
-
-from cachetools import TTLCache
+from typing import Any, Callable, Final, Iterable, Mapping, TypeVar
 
 from streamlit import env_util
 
@@ -202,37 +199,3 @@ def extract_key_query_params(
         ]
         for item in sublist
     }
-
-
-K = TypeVar("K")
-V = TypeVar("V")
-
-
-class TimedCleanupCache(TTLCache, Generic[K, V]):
-    """A TTLCache that asynchronously expires its entries."""
-
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
-        self._task: asyncio.Task[Any] | None = None
-
-    def __setitem__(self, key: K, value: V) -> None:
-        # Set an expiration task to run periodically
-        # Can't be created in init because that only runs once and
-        # the event loop might not exist yet.
-        if self._task is None:
-            try:
-                self._task = asyncio.create_task(expire_cache(self))
-            except RuntimeError:
-                # Just continue if the event loop isn't started yet.
-                pass
-        super().__setitem__(key, value)
-
-    def __del__(self):
-        if self._task is not None:
-            self._task.cancel()
-
-
-async def expire_cache(cache: TTLCache) -> None:
-    while True:
-        await asyncio.sleep(30)
-        cache.expire()

lib/tests/streamlit/util_test.py

@@ -12,8 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import asyncio
-import gc
 import random
 import unittest
 from typing import Dict, List, Set
@@ -187,26 +185,3 @@ def test_calc_md5_can_handle_bytes_and_strings(self):
             util.calc_md5("eventually bytes"),
             util.calc_md5("eventually bytes".encode("utf-8")),
         )
-
-    def test_timed_cleanup_cache_gc(self):
-        """Test that the TimedCleanupCache does not leave behind tasks when
-        the cache is not externally reachable"""
-        loop = asyncio.new_event_loop()
-        asyncio.set_event_loop(loop)
-
-        async def create_cache():
-            cache = util.TimedCleanupCache(maxsize=2, ttl=10)
-            cache["foo"] = "bar"
-
-            # expire_cache and create_cache
-            assert len(asyncio.all_tasks()) > 1
-
-        asyncio.run(create_cache())
-
-        gc.collect()
-
-        async def check():
-            # Only has this function running
-            assert len(asyncio.all_tasks()) == 1
-
-        asyncio.run(check())