cache: add Size method to LRU cache with test updates

cache/cache.go

@@ -26,4 +26,8 @@ type Cache[K comparable, V Value] interface {
 
 	// Len returns number of elements in the cache.
 	Len() int
+
+	// Size returns the total size of all elements in the cache. It uses
+	// the same units produced by V.Size().
+	Size() uint64
 }

cache/lru/lru.go

@@ -282,3 +282,12 @@ func (c *Cache[K, V]) RangeFIFO(visitor func(K, V) bool) {
 		}
 	}
 }
+
+// Size returns the total size of all elements in the cache. It uses
+// the same units produced by V.Size().
+func (c *Cache[K, V]) Size() uint64 {
+	c.mtx.RLock()
+	defer c.mtx.RUnlock()
+
+	return c.size
+}

cache/lru/lru_test.go

@@ -105,7 +105,7 @@ func TestElementSizeCapacityEvictsEverything(t *testing.T) {
 	c.Put(1, &sizeable{value: 1, size: 1})
 	c.Put(2, &sizeable{value: 2, size: 2})
 	c.Put(3, &sizeable{value: 3, size: 3})
-	require.Equal(t, c.size, uint64(6))
+	require.Equal(t, c.Size(), uint64(6))
 
 	// Insert element with size=capacity of cache.
 	c.Put(4, &sizeable{value: 4, size: 6})
@@ -326,7 +326,7 @@ func TestLoadAndDelete(t *testing.T) {
 
 	// The length should be 0.
 	require.Zero(t, c.Len())
-	require.Zero(t, c.size)
+	require.Zero(t, c.Size())
 }
 
 // TestRangeIteration checks that the `Range` method works as expected.