Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/718#discussion_r13397985
--- Diff:
core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala ---
@@ -0,0 +1,203 @@
+/*
+ * 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.deploy.history
+
+import java.io.FileNotFoundException
+import java.util.concurrent.atomic.AtomicReference
+
+import scala.collection.mutable
+
+import org.apache.hadoop.fs.{FileStatus, Path}
+
+import org.apache.spark.{Logging, SecurityManager, SparkConf}
+import org.apache.spark.scheduler._
+import org.apache.spark.ui.SparkUI
+import org.apache.spark.util.Utils
+
+private[history] class FsHistoryProvider(conf: SparkConf) extends
ApplicationHistoryProvider
+ with Logging {
+
+ // Interval between each check for event log updates
+ private val UPDATE_INTERVAL_MS =
conf.getInt("spark.history.fs.updateInterval", 10) * 1000
+
+ private val logDir = conf.get("spark.history.fs.logDirectory")
+ private val fs = Utils.getHadoopFileSystem(logDir)
+
+ // A timestamp of when the disk was last accessed to check for log
updates
+ private var lastLogCheckTimeMs = -1L
+
+ // List of applications, in order from newest to oldest.
+ private val appList = new
AtomicReference[Seq[ApplicationHistoryInfo]](Nil)
--- End diff --
It's not a performance thing, but a correctness thing, since the variable
is accessed by different threads (one of which might be writing to it). You
really don't two threads, one adding things to an ArrayBuffer while the other
is trying to iterate through it, for example. That will end up in tears.
That being said, since the code is only reading and writing to the variable
(and not making other kinds of non-atomic changes), volatile is probably
enough. A lock is way overkill here.
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