Thanks for this great software! In my usage scenario, i observed that cache size keep

I think there is still a problem here. If a node is in both the <code class="notransla

Bug Report: v3.0.0 gc may failed about ccache HOT 5 CLOSED

karlseguin commented on July 23, 2024

Bug Report: v3.0.0 gc may failed

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Comments (5)

karlseguin commented on July 23, 2024 2

thanks for the detailed report, it really helped narrow it down. I added a slightly modified version of your test :)

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stormluke commented on July 23, 2024

I think there is still a problem here. If a node is in both the deletables and the promotables, and deletables is consumed before promotables, the node will be Remove() twice, causing gc() to fail.

deletables -> doDelete() -> Remove()
promotables -> doPromote() -> MoveToFront() -> Remove()
gc() node == nil, then fail

If you keep this test case running, it will fail

func Test_CachePrune(t *testing.T) {
	maxSize := int64(500)
	cache := New(Configure[string]().MaxSize(maxSize).ItemsToPrune(50))
	epoch := 0
	for {
		epoch += 1
		expired := make([]string, 0)
		for i := 0; i < 50; i += 1 {
			key := strconv.FormatInt(rand.Int63n(maxSize*20), 10)
			item := cache.Get(key)
			if item == nil || item.TTL() > 1*time.Minute {
				expired = append(expired, key)
			}
		}
		for _, key := range expired {
			cache.Set(key, key, 5*time.Minute)
		}
		if epoch%500 == 0 {
			fmt.Printf("size=%d, dropped=%d\n", cache.GetSize(), cache.GetDropped())
		}
		if cache.GetSize() > 5000 {
			fmt.Printf("size=%d, dropped=%d\n", cache.GetSize(), cache.GetDropped())
			t.Fail()
			return
		}
	}
}

I think the fix is let list.node = nil (and maybe item.promotions = -2) after Remove() in doDelete(), same as in gc().

func (c *Cache[T]) doDelete(item *Item[T]) {
	if item.node == nil {
		item.promotions = -2
	} else {
		c.size -= item.size
		if c.onDelete != nil {
			c.onDelete(item)
		}
		c.list.Remove(item.node)
		item.node = nil // fix
                item.promotions = -2 // fix
	}
}