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package cache
import (
"container/list"
"sync"
)
// BufferLRU implements an object cache with an LRU eviction policy and a
// maximum size (measured in object size).
type BufferLRU struct {
MaxSize FileSize
actualSize FileSize
ll *list.List
cache map[int64]*list.Element
mut sync.Mutex
}
// NewBufferLRU creates a new BufferLRU with the given maximum size. The maximum
// size will never be exceeded.
func NewBufferLRU(maxSize FileSize) *BufferLRU {
return &BufferLRU{MaxSize: maxSize}
}
// NewBufferLRUDefault creates a new BufferLRU with the default cache size.
func NewBufferLRUDefault() *BufferLRU {
return &BufferLRU{MaxSize: DefaultMaxSize}
}
type buffer struct {
Key int64
Slice []byte
}
// Put puts a buffer into the cache. If the buffer is already in the cache, it
// will be marked as used. Otherwise, it will be inserted. A buffers might
// be evicted to make room for the new one.
func (c *BufferLRU) Put(key int64, slice []byte) {
c.mut.Lock()
defer c.mut.Unlock()
if c.cache == nil {
c.actualSize = 0
c.cache = make(map[int64]*list.Element, 1000)
c.ll = list.New()
}
bufSize := FileSize(len(slice))
if ee, ok := c.cache[key]; ok {
oldBuf := ee.Value.(buffer)
// in this case bufSize is a delta: new size - old size
bufSize -= FileSize(len(oldBuf.Slice))
c.ll.MoveToFront(ee)
ee.Value = buffer{key, slice}
} else {
if bufSize > c.MaxSize {
return
}
ee := c.ll.PushFront(buffer{key, slice})
c.cache[key] = ee
}
c.actualSize += bufSize
for c.actualSize > c.MaxSize {
last := c.ll.Back()
lastObj := last.Value.(buffer)
lastSize := FileSize(len(lastObj.Slice))
c.ll.Remove(last)
delete(c.cache, lastObj.Key)
c.actualSize -= lastSize
}
}
// Get returns a buffer by its key. It marks the buffer as used. If the buffer
// is not in the cache, (nil, false) will be returned.
func (c *BufferLRU) Get(key int64) ([]byte, bool) {
c.mut.Lock()
defer c.mut.Unlock()
ee, ok := c.cache[key]
if !ok {
return nil, false
}
c.ll.MoveToFront(ee)
return ee.Value.(buffer).Slice, true
}
// Clear the content of this buffer cache.
func (c *BufferLRU) Clear() {
c.mut.Lock()
defer c.mut.Unlock()
c.ll = nil
c.cache = nil
c.actualSize = 0
}
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