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call evict on replacing value #135

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Jun 21, 2023
Merged

call evict on replacing value #135

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3 changes: 3 additions & 0 deletions simplelru/lru.go
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,9 @@ func (c *LRU[K, V]) Add(key K, value V) (evicted bool) {
// Check for existing item
if ent, ok := c.items[key]; ok {
c.evictList.moveToFront(ent)
if c.onEvict != nil {
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there is an alternative way that use the lru.ContainsOrAdd interface and check exist boolean return

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curious why onEvict needs to be called when adding an existing item?
This caused issue in our use case, where we used gRPC channel as ent.value, and onEvict will close the channel unexpectedly if we try to add that existing channel again

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I'll leave it for maintainers of this project to make the call

  • the value is dropped from cache, and some projects rely on evict callback to cleanup (cgo project will also free memory), in some race condition it can cause memory leak and hard to trace
  • in your usecase you can use the somewhat side-effect free ContainsOrAdd

p/s: not sure why you adding back grpc connection to the cache that you just picked from

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I understand using evict when item is dropped from cache. But in this code block, why do we need to drop from cache? Isn't c.evictList.moveToFront(ent) is enough and the item should still be kept in the cache?

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you can see right after that the value is overrided with new value, so old value is drop, in your usecase it seems both values are same

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I see, this behavior came as a surprise for us, as we had a large cache size and didn't expect evict callback to be triggered. Anyways, we can use something like ContainsOrAdd as you suggested

c.onEvict(key, ent.value)
}
ent.value = value
return false
}
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