plumbing/cache: change FIFO to LRU cache

1 files changed, 84 insertions, 0 deletions

diff --git a/plumbing/cache/object_lru.go b/plumbing/cache/object_lru.go
new file mode 100644
index 0000000..e4c3160
--- /dev/null
+++ b/plumbing/cache/object_lru.go
@@ -0,0 +1,84 @@
+package cache
+
+import (
+	"container/list"
+
+	"gopkg.in/src-d/go-git.v4/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
+}
+
+// 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}
+}
+
+// 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) {
+	if c.cache == nil {
+		c.actualSize = 0
+		c.cache = make(map[interface{}]*list.Element, 1000)
+		c.ll = list.New()
+	}
+
+	key := obj.Hash()
+	if ee, ok := c.cache[key]; ok {
+		c.ll.MoveToFront(ee)
+		ee.Value = obj
+		return
+	}
+
+	objSize := FileSize(obj.Size())
+
+	if objSize >= c.MaxSize {
+		return
+	}
+
+	if c.actualSize+objSize > c.MaxSize {
+		last := c.ll.Back()
+		lastObj := last.Value.(plumbing.EncodedObject)
+		lastSize := FileSize(lastObj.Size())
+
+		c.ll.Remove(last)
+		delete(c.cache, lastObj.Hash())
+		c.actualSize -= lastSize
+
+		if c.actualSize+objSize > c.MaxSize {
+			return
+		}
+	}
+
+	ee := c.ll.PushFront(obj)
+	c.cache[key] = ee
+	c.actualSize += objSize
+}
+
+// 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) {
+	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.ll = nil
+	c.cache = nil
+	c.actualSize = 0
+}