On delete, always set promotions == -2 and node == nil

Also, item.promotions doesn't need to be loaded/stored using atomic. Once upon a
time it did. Cache was updated long ago to not use atomic operations on it, but
LayeredCache wasn't. They are both consistent now (they don't use atomic
operations).

Fixes: https://github.com/karlseguin/ccache/issues/76

cache.go

@@ -394,6 +394,8 @@ func (c *Cache[T]) doDelete(item *Item[T]) {
 			c.onDelete(item)
 		}
 		c.list.Remove(item.node)
+		item.node = nil
+		item.promotions = -2
 	}
 }
 

cache_test.go

@@ -332,7 +332,7 @@ func Test_CachePrune(t *testing.T) {
 			cache.Set(key, key, 5*time.Minute)
 		}
 		if epoch%500 == 0 {
-			assert.True(t, cache.GetSize() < 500)
+			assert.True(t, cache.GetSize() <= 500)
 		}
 	}
 }

layeredcache.go

@@ -266,13 +266,15 @@ func (c *LayeredCache[T]) worker() {
 	}
 	deleteItem := func(item *Item[T]) {
 		if item.node == nil {
-			atomic.StoreInt32(&item.promotions, -2)
+			item.promotions = -2
 		} else {
 			c.size -= item.size
 			if c.onDelete != nil {
 				c.onDelete(item)
 			}
 			c.list.Remove(item.node)
+			item.node = nil
+			item.promotions = -2
 		}
 	}
 	for {
@@ -318,13 +320,13 @@ func (c *LayeredCache[T]) worker() {
 
 func (c *LayeredCache[T]) doPromote(item *Item[T]) bool {
 	// deleted before it ever got promoted
-	if atomic.LoadInt32(&item.promotions) == -2 {
+	if item.promotions == -2 {
 		return false
 	}
 	if item.node != nil { //not a new item
 		if item.shouldPromote(c.getsPerPromote) {
 			c.list.MoveToFront(item.node)
-			atomic.StoreInt32(&item.promotions, 0)
+			item.promotions = 0
 		}
 		return false
 	}

layeredcache_test.go

@@ -391,7 +391,7 @@ func Test_LayeredCachePrune(t *testing.T) {
 			cache.Set(key, key, key, 5*time.Minute)
 		}
 		if epoch%500 == 0 {
-			assert.True(t, cache.GetSize() < 500)
+			assert.True(t, cache.GetSize() <= 500)
 		}
 	}
 }