fix(memory): reject a cleanup_interval that is not positive

CHANGELOG.md

@@ -87,6 +87,12 @@ Note that 0.3.3 was never released; 0.3.4 follows 0.3.2.
   `delete()` and the other methods let the error through.
   ([#177](https://github.com/allen0099/FastAPI-CacheX/issues/177))
 
+- **`MemoryBackend` rejects a `cleanup_interval` that is not positive.** With
+  `0` or a negative value, `asyncio.sleep()` returned at once and the cleanup
+  loop spun, using a full CPU core and taking the cache lock on every pass. It
+  now raises `ValueError`.
+  ([#180](https://github.com/allen0099/FastAPI-CacheX/issues/180))
+
 ## [0.3.7] - 2026-09-25
 
 ### Added

docs/BACKENDS.md

@@ -19,7 +19,8 @@ All backends namespace their keys with a prefix (`fastapi_cachex:` by default,
 
 If you don't specify a backend, FastAPI-CacheX will use the in-memory cache by default.
 This is suitable for development and testing purposes. The backend automatically runs
-a cleanup task to remove expired entries every 60 seconds (`MemoryBackend(cleanup_interval=60)`).
+a cleanup task to remove expired entries every 60 seconds (`MemoryBackend(cleanup_interval=60)`;
+the interval must be positive).
 
 ```python
 from fastapi_cachex.backends import MemoryBackend

fastapi_cachex/backends/memory.py

@@ -56,7 +56,15 @@ def __init__(self, cleanup_interval: int = 60) -> None:
 
         Args:
             cleanup_interval: Interval in seconds between cleanup runs (default: 60)
+
+        Raises:
+            ValueError: If ``cleanup_interval`` is not positive
         """
+        if cleanup_interval <= 0:
+            # asyncio.sleep() returns at once for these, so the cleanup loop
+            # would spin, taking the cache lock on every pass.
+            msg = f"cleanup_interval must be positive, got {cleanup_interval!r}"
+            raise ValueError(msg)
         self.cache: dict[str, CacheItem] = {}
         self.lock = asyncio.Lock()
         self.cleanup_interval = cleanup_interval

i18n/zh-TW/docs/BACKENDS.md

@@ -15,7 +15,7 @@
 
 ## 記憶體（預設） {#in-memory-default}
 
-若未指定後端，FastAPI-CacheX 預設會使用記憶體快取。這適合開發與測試用途。此後端會自動執行清理工作，每 60 秒移除一次已過期的項目（`MemoryBackend(cleanup_interval=60)`）。
+若未指定後端，FastAPI-CacheX 預設會使用記憶體快取。這適合開發與測試用途。此後端會自動執行清理工作，每 60 秒移除一次已過期的項目（`MemoryBackend(cleanup_interval=60)`；間隔必須大於 0）。
 
 ```python
 from fastapi_cachex.backends import MemoryBackend

tests/backends/test_memory.py

@@ -16,6 +16,13 @@ def memory_backend():
     return MemoryBackend()
 
 
+@pytest.mark.parametrize("interval", [0, -5])
+def test_cleanup_interval_must_be_positive(interval: int) -> None:
+    """A non-positive interval made the cleanup loop spin (#180)."""
+    with pytest.raises(ValueError, match="cleanup_interval must be positive"):
+        MemoryBackend(cleanup_interval=interval)
+
+
 @pytest.mark.asyncio
 async def test_memory_backend_set_get(memory_backend: MemoryBackend):
     key = "test_key"