Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/2416#discussion_r17923757
--- Diff:
core/src/main/scala/org/apache/spark/util/collection/Spillable.scala ---
@@ -0,0 +1,102 @@
+/*
+ * 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.collection
+
+import org.apache.spark.SparkEnv
+import scala.language.reflectiveCalls
+
+/**
+ * Spills contents of an in-memory collection to disk when the memory
threshold
+ * has been exceeded.
+ *
+ * @tparam C collection type that provides a size estimate
+ */
+private[spark] trait Spillable[C <: { def estimateSize(): Long }] {
+
+ // Number of elements read from input since last spill
+ protected[this] var elementsRead: Long
+
+ // Memory manager that can be used to acquire/release memory
+ private[this] val shuffleMemoryManager =
SparkEnv.get.shuffleMemoryManager
+
+ // What threshold of elementsRead we start estimating collection size at
+ private[this] val trackMemoryThreshold = 1000
+
+ // How much of the shared memory pool this collection has claimed
+ private[this] var myMemoryThreshold = 0L
+
+ // Number of bytes spilled in total
+ private[this] var _memoryBytesSpilled = 0L
+
+ // Number of spills
+ private[this] var _spillCount = 0
+
+ /**
+ * Spills the current in-memory collection to disk if needed. Attempts
to acquire more
+ * memory before spilling.
+ *
+ * @tparam A type of collection to be spilled
+ * @return if spilled, a new empty collection instance; otherwise, the
same collection instance
+ */
+ protected[this] def maybeSpill[A <: C](collection: A): A = {
+ if (elementsRead > trackMemoryThreshold && elementsRead % 32 == 0 &&
+ collection.estimateSize() >= myMemoryThreshold) {
+ // Claim up to double our current memory from the shuffle memory pool
+ val currentMemory = collection.estimateSize()
+ val amountToRequest = 2 * currentMemory - myMemoryThreshold
+ val granted = shuffleMemoryManager.tryToAcquire(amountToRequest)
+ myMemoryThreshold += granted
+ if (myMemoryThreshold <= currentMemory) {
+ // We were granted too little memory to grow further (either
tryToAcquire returned 0,
+ // or we already had more memory than myMemoryThreshold); spill
the current collection
+ _spillCount += 1
+ val empty = spill[A](collection)
+ _memoryBytesSpilled += currentMemory
+ release()
+ return empty
+ }
+ }
+ collection
+ }
+
+ /**
+ * Spills the current in-memory collection to disk, and releases the
memory.
+ *
+ * @param collection collection to spill to disk
+ * @return new, empty collection
+ */
+ protected[this] def spill[A <: C](collection: A): A
+
+ /**
+ * @return total number of times this collection was spilled
+ */
+ protected[this] def spillCount: Int = _spillCount
--- End diff --
Same here, no need for `this`
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