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Add a helper method to set eviction function after construction #318

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Nov 4, 2024
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Add a helper method to set eviction function after construction #318

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10 changes: 10 additions & 0 deletions lru/lru.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ limitations under the License.
package lru

import (
"fmt"
"sync"

groupcache "k8s.io/utils/internal/third_party/forked/golang/golang-lru"
Expand Down Expand Up @@ -44,6 +45,15 @@ func NewWithEvictionFunc(size int, f EvictionFunc) *Cache {
return c
}

// SetEvictionFunc updates the eviction func
func (c *Cache) SetEvictionFunc(f EvictionFunc) error {
if c.cache.OnEvicted != nil {
return fmt.Errorf("lru cache eviction function is already set")
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}
c.cache.OnEvicted = f
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should be thread safe and lock before setting the value?

same for NewWithEvictionFunc?

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good point! added it here. But we don't need it in NewWithEvictionFunc as we do not return the internal Cache we create for the user to use until the method exits, so setting c.cache.OnEvicted = f without the locks are fine.

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good point! added it here

was that added in a follow-up? not seeing it here

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@liggitt would you recommend both the lock/unlock in addition to the "return error if it is already set"? i can cut another PR if so

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@liggitt would you recommend both the lock/unlock in addition to the "return error if it is already set"?

yeah... going from nil to set still requires a lock since the function can be read/used concurrently from other methods

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(and disallowing resetting it once set still sgtm)

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Follow up is here #319

return nil
}

// Add adds a value to the cache.
func (c *Cache) Add(key Key, value interface{}) {
c.lock.Lock()
Expand Down
28 changes: 28 additions & 0 deletions lru/lru_test.go
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Expand Up @@ -130,3 +130,31 @@ func TestEviction(t *testing.T) {
t.Errorf("unexpected eviction data: key=%v val=%v", seenKey, seenVal)
}
}

func TestSetEviction(t *testing.T) {
var seenKey Key
var seenVal interface{}

lru := New(1)

err := lru.SetEvictionFunc(func(key Key, value interface{}) {
seenKey = key
seenVal = value
})

if err != nil {
t.Errorf("unexpected error setting eviction function: %v", err)
}

lru.Add(1, 2)
lru.Add(3, 4)

if seenKey != 1 || seenVal != 2 {
t.Errorf("unexpected eviction data: key=%v val=%v", seenKey, seenVal)
}

err = lru.SetEvictionFunc(func(key Key, value interface{}) {})
if err == nil {
t.Errorf("expected error but got none")
}
}
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