Added random eviction functionality

hashmap/rand_evict.go

@@ -0,0 +1,43 @@
+// Copyright 2012 Apcera Inc. All rights reserved.
+
+package hashmap
+
+import (
+	"math/rand"
+	"time"
+)
+
+// We use init to setup the random number generator
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+// RemoveRandom can be used for a random policy eviction.
+// This is stochastic but very fast and does not impedede
+// performance like LRU, LFU or even ARC based implementations.
+func (h *HashMap) RemoveRandom() {
+	if h.used == 0 {
+		return
+	}
+	index := (rand.Int())&int(h.msk)
+	// Walk forward til we find an entry
+	for i := index ; i < len(h.bkts) ; i++ {
+		e := &h.bkts[i]
+		if *e != nil {
+			*e = (*e).next
+			h.used -= 1
+			return
+		}
+	}
+	// If we are here we hit end and did not remove anything,
+	// use the index and walk backwards.
+	for i := index ; i >= 0 ; i-- {
+		e := &h.bkts[i]
+		if *e != nil {
+			*e = (*e).next
+			h.used -= 1
+			return
+		}
+	}
+	panic("Should not reach here..")
+}