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package cache
import (
"container/list"
"sync"
"github.com/go-git/go-git/v5/plumbing"
)
// ObjectLRU implements an object cache with an LRU eviction policy and a
// maximum size (measured in object size).
type ObjectLRU struct {
MaxSize FileSize
actualSize FileSize
ll *list.List
cache map[interface{}]*list.Element
mut sync.Mutex
}
// NewObjectLRU creates a new ObjectLRU with the given maximum size. The maximum
// size will never be exceeded.
func NewObjectLRU(maxSize FileSize) *ObjectLRU {
return &ObjectLRU{MaxSize: maxSize}
}
// NewObjectLRUDefault creates a new ObjectLRU with the default cache size.
func NewObjectLRUDefault() *ObjectLRU {
return &ObjectLRU{MaxSize: DefaultMaxSize}
}
// Put puts an object into the cache. If the object is already in the cache, it
// will be marked as used. Otherwise, it will be inserted. A single object might
// be evicted to make room for the new object.
func (c *ObjectLRU) Put(obj plumbing.EncodedObject) {
c.mut.Lock()
defer c.mut.Unlock()
if c.cache == nil {
c.actualSize = 0
c.cache = make(map[interface{}]*list.Element, 1000)
c.ll = list.New()
}
objSize := FileSize(obj.Size())
key := obj.Hash()
if ee, ok := c.cache[key]; ok {
oldObj := ee.Value.(plumbing.EncodedObject)
// in this case objSize is a delta: new size - old size
objSize -= FileSize(oldObj.Size())
c.ll.MoveToFront(ee)
ee.Value = obj
} else {
if objSize > c.MaxSize {
return
}
ee := c.ll.PushFront(obj)
c.cache[key] = ee
}
c.actualSize += objSize
for c.actualSize > c.MaxSize {
last := c.ll.Back()
if last == nil {
c.actualSize = 0
break
}
lastObj := last.Value.(plumbing.EncodedObject)
lastSize := FileSize(lastObj.Size())
c.ll.Remove(last)
delete(c.cache, lastObj.Hash())
c.actualSize -= lastSize
}
}
// Get returns an object by its hash. It marks the object as used. If the object
// is not in the cache, (nil, false) will be returned.
func (c *ObjectLRU) Get(k plumbing.Hash) (plumbing.EncodedObject, bool) {
c.mut.Lock()
defer c.mut.Unlock()
ee, ok := c.cache[k]
if !ok {
return nil, false
}
c.ll.MoveToFront(ee)
return ee.Value.(plumbing.EncodedObject), true
}
// Clear the content of this object cache.
func (c *ObjectLRU) Clear() {
c.mut.Lock()
defer c.mut.Unlock()
c.ll = nil
c.cache = nil
c.actualSize = 0
}
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