handle zero capacity for lru cache (#20080)

Author: altendky

chia/_tests/core/util/test_lru_cache.py

@@ -2,6 +2,8 @@
 
 import unittest
 
+import pytest
+
 from chia.util.lru_cache import LRUCache
 
 
@@ -54,3 +56,17 @@ def test_lru_cache(self):
         assert len(cache.cache) == 5
         assert cache.get(b"0") is None
         assert cache.get(b"1") == 1
+
+
+@pytest.mark.parametrize(argnames="capacity", argvalues=[-10, -1, 0])
+def test_with_zero_capacity(capacity: int) -> None:
+    cache: LRUCache[bytes, int] = LRUCache(capacity=capacity)
+    cache.put(b"0", 1)
+    assert cache.get(b"0") is None
+    assert len(cache.cache) == 0
+
+
+@pytest.mark.parametrize(argnames="capacity", argvalues=[-10, -1, 0, 1, 5, 10])
+def test_get_capacity(capacity: int) -> None:
+    cache: LRUCache[object, object] = LRUCache(capacity=capacity)
+    assert cache.get_capacity() == capacity

chia/util/lru_cache.py

@@ -22,10 +22,14 @@ def get(self, key: K) -> Optional[V]:
             return self.cache[key]
 
     def put(self, key: K, value: V) -> None:
-        self.cache[key] = value
-        self.cache.move_to_end(key)
-        if len(self.cache) > self.capacity:
-            self.cache.popitem(last=False)
+        if self.capacity > 0:
+            self.cache[key] = value
+            self.cache.move_to_end(key)
+            if len(self.cache) > self.capacity:
+                self.cache.popitem(last=False)
 
     def remove(self, key: K) -> None:
         self.cache.pop(key)
+
+    def get_capacity(self) -> int:
+        return self.capacity