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-rw-r--r--plumbing/cache/buffer_lru.go98
1 files changed, 98 insertions, 0 deletions
diff --git a/plumbing/cache/buffer_lru.go b/plumbing/cache/buffer_lru.go
new file mode 100644
index 0000000..acaf195
--- /dev/null
+++ b/plumbing/cache/buffer_lru.go
@@ -0,0 +1,98 @@
+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
+}