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