Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/126#discussion_r10552981
--- Diff: core/src/main/scala/org/apache/spark/util/BoundedHashMap.scala ---
@@ -0,0 +1,67 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.spark.util
+
+import scala.collection.mutable.{ArrayBuffer, SynchronizedMap}
+
+import java.util.{Collections, LinkedHashMap}
+import java.util.Map.{Entry => JMapEntry}
+import scala.reflect.ClassTag
+
+/**
+ * A map that upper bounds the number of key-value pairs present in it. It
can be configured to
+ * drop the least recently user pair or the earliest inserted pair. It
exposes a
+ * scala.collection.mutable.Map interface to allow it to be a drop-in
replacement for Scala
+ * HashMaps.
+ *
+ * Internally, a Java LinkedHashMap is used to get insert-order or
access-order behavior.
+ * Note that the LinkedHashMap is not thread-safe and hence, it is wrapped
in a
+ * Collections.synchronizedMap. However, getting the Java HashMap's
iterator and
+ * using it can still lead to ConcurrentModificationExceptions. Hence, the
iterator()
+ * function is overridden to copy the all pairs into an ArrayBuffer and
then return the
+ * iterator to the ArrayBuffer. Also, the class apply the trait
SynchronizedMap which
+ * ensures that all calls to the Scala Map API are synchronized. This
together ensures
+ * that ConcurrentModificationException is never thrown.
+ *
+ * @param bound max number of key-value pairs
+ * @param useLRU true = least recently used/accessed will be dropped when
bound is reached,
+ * false = earliest inserted will be dropped
+ */
+private[spark] class BoundedHashMap[A, B](bound: Int, useLRU: Boolean)
+ extends WrappedJavaHashMap[A, B, A, B] with SynchronizedMap[A, B] {
+
+ protected[util] val internalJavaMap = Collections.synchronizedMap(new
LinkedHashMap[A, B](
+ bound / 8, (0.75).toFloat, useLRU) {
+ override protected def removeEldestEntry(eldest: JMapEntry[A, B]):
Boolean = {
+ size() > bound
+ }
+ })
+
+ protected[util] def newInstance[K1, V1](): WrappedJavaHashMap[K1, V1, _,
_] = {
--- End diff --
what does protected[util] mean in Scala? You can access it in all child
classes of all classes in util? Pretty confusing here
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