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package cache
import "errors"
type EvictionPolicyType int
const (
PolicyNone EvictionPolicyType = iota
PolicyFIFO
PolicyLRU
PolicyLFU
PolicyLTR
)
type evictionStrategies interface {
OnInsert(n *node)
OnAccess(n *node)
Evict() *node
}
type evictionPolicy struct {
evictionStrategies
Type EvictionPolicyType
evict *node
}
func (e *evictionPolicy) SetPolicy(y EvictionPolicyType) error {
store := map[EvictionPolicyType]func() evictionStrategies{
PolicyNone: func() evictionStrategies {
return nonePolicy{evict: e.evict}
},
PolicyFIFO: func() evictionStrategies {
return fifoPolicy{evict: e.evict}
},
PolicyLRU: func() evictionStrategies {
return lruPolicy{evict: e.evict}
},
PolicyLFU: func() evictionStrategies {
return lfuPolicy{evict: e.evict}
},
}
factory, ok := store[y]
if !ok {
return errors.New("invalid olicy")
}
e.evictionStrategies = factory()
return nil
}
type nonePolicy struct {
evict *node
}
func (s nonePolicy) OnInsert(node *node) {
node.EvictPrev = s.evict
node.EvictNext = node.EvictPrev.EvictNext
node.EvictNext.EvictPrev = node
node.EvictPrev.EvictNext = node
}
func (nonePolicy) OnAccess(n *node) {
}
func (nonePolicy) Evict() *node {
return nil
}
type fifoPolicy struct {
evict *node
}
func (s fifoPolicy) OnInsert(node *node) {
node.EvictPrev = s.evict
node.EvictNext = node.EvictPrev.EvictNext
node.EvictNext.EvictPrev = node
node.EvictPrev.EvictNext = node
}
func (fifoPolicy) OnAccess(n *node) {
}
func (s fifoPolicy) Evict() *node {
if s.evict.EvictPrev != s.evict {
return s.evict.EvictPrev
} else {
return nil
}
}
type lruPolicy struct {
evict *node
}
func (s lruPolicy) OnInsert(node *node) {
node.EvictPrev = s.evict
node.EvictNext = node.EvictPrev.EvictNext
node.EvictNext.EvictPrev = node
node.EvictPrev.EvictNext = node
}
func (s lruPolicy) OnAccess(node *node) {
node.EvictNext.EvictPrev = node.EvictPrev
node.EvictPrev.EvictNext = node.EvictNext
node.EvictPrev = s.evict
node.EvictNext = node.EvictPrev.EvictNext
node.EvictNext.EvictPrev = node
node.EvictPrev.EvictNext = node
}
func (s lruPolicy) Evict() *node {
if s.evict.EvictPrev != s.evict {
return s.evict.EvictPrev
} else {
return nil
}
}
type lfuPolicy struct {
evict *node
}
func (s lfuPolicy) OnInsert(node *node) {
node.EvictPrev = s.evict
node.EvictNext = node.EvictPrev.EvictNext
node.EvictNext.EvictPrev = node
node.EvictPrev.EvictNext = node
node.Access = 0
}
func (s lfuPolicy) OnAccess(node *node) {
node.Access++
for v := node.EvictPrev; v.EvictPrev != s.evict; v = v.EvictPrev {
if v.Access <= node.Access {
node.EvictNext.EvictPrev = node.EvictPrev
node.EvictPrev.EvictNext = node.EvictNext
node.EvictPrev = v
node.EvictNext = node.EvictPrev.EvictNext
node.EvictNext.EvictPrev = node
node.EvictPrev.EvictNext = node
return
}
}
node.EvictNext.EvictPrev = node.EvictPrev
node.EvictPrev.EvictNext = node.EvictNext
node.EvictPrev = s.evict
node.EvictNext = node.EvictPrev.EvictNext
node.EvictNext.EvictPrev = node
node.EvictPrev.EvictNext = node
}
func (s lfuPolicy) Evict() *node {
if s.evict.EvictPrev != s.evict {
return s.evict.EvictPrev
} else {
return nil
}
}
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