Merge pull request #136 from twitter/feature/fix_mutable_cache

Fix MutableCache Bug

storehaus-cache/src/main/scala/com/twitter/storehaus/cache/MutableLRUCache.scala

@@ -31,7 +31,7 @@ object MutableLRUCache {
 }
 
 class MutableLRUCache[K, V](capacity: Int) extends JMapCache[K, V](() =>
-  new JLinkedHashMap[K, V](capacity + 1, 0.75f) {
+  new JLinkedHashMap[K, V](capacity + 1, 0.75f, true) {
     override protected def removeEldestEntry(eldest: JMap.Entry[K, V]) =
       super.size > capacity
   }) {

storehaus-cache/src/test/scala/com/twitter/storehaus/cache/MutableLRUCacheTest.scala

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2013 Twitter Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License. You may obtain
+ * a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.twitter.storehaus.cache
+
+import org.specs._
+
+class MutableLRUCacheTest extends Specification {
+  def freshCache = MutableLRUCache[String, Int](2)
+
+  def checkCache(pairs: Seq[(String, Int)], results: Seq[Boolean]) = {
+    val cache = freshCache
+    pairs.foreach(cache += _)
+    pairs.map { case (k, _) => cache.contains(k) } must be_==(results)
+  }
+
+  "MutableLRUCache works properly with threshold 2" in {
+    // At capacity
+    checkCache(
+      Seq("a" -> 1, "b" -> 2),
+      Seq(true, true)
+    )
+    // a is touched, so b and c are evicted
+    checkCache(
+      Seq("a" -> 1, "b" -> 2, "c" -> 3, "a" -> 1, "d" -> 4),
+      Seq(true, false, false, true, true)
+    )
+  }
+}