Review comments.

Author: Marcelo Vanzin

core/src/main/scala/org/apache/spark/deploy/history/FsHistoryProvider.scala

@@ -271,6 +271,8 @@ private[history] class FsHistoryProvider(conf: SparkConf) extends ApplicationHis
    * Loads a legacy log directory. This assumes that the log directory contains a single event
    * log file (along with other metadata files), which is the case for directories generated by
    * the code in previous releases.
+   *
+   * @return 2-tuple of (input stream of the events, version of Spark which wrote the log)
    */
   private[history] def openLegacyEventLog(dir: Path): (InputStream, String) = {
     val children = fs.listStatus(dir)
@@ -293,21 +295,27 @@ private[history] class FsHistoryProvider(conf: SparkConf) extends ApplicationHis
       }
     }
 
+    if (eventLogPath == null || sparkVersion == null) {
+      throw new IllegalArgumentException(s"$dir is not a Spark application log directory.")
+    }
+
     val codec = try {
         codecName.map { c => CompressionCodec.createCodec(conf, c) }
       } catch {
         case e: Exception =>
           throw new IllegalArgumentException(s"Unknown compression codec $codecName.")
       }
 
-    if (eventLogPath == null || sparkVersion == null) {
-      throw new IllegalArgumentException(s"$dir is not a Spark application log directory.")
-    }
-
     val in = new BufferedInputStream(fs.open(eventLogPath))
     (codec.map(_.compressedInputStream(in)).getOrElse(in), sparkVersion)
   }
 
+  /**
+   * Return whether the specified event log path contains a old directory-based event log.
+   * Previously, the event log of an application comprises of multiple files in a directory.
+   * As of Spark 1.3, these files are consolidated into a single one that replaces the directory.
+   * See SPARK-2261 for more detail.
+   */
   private def isLegacyLogDirectory(entry: FileStatus): Boolean = entry.isDir()
 
   private def getModificationTime(fsEntry: FileStatus): Long = {

core/src/main/scala/org/apache/spark/scheduler/EventLoggingListener.scala

@@ -87,7 +87,7 @@ private[spark] class EventLoggingListener(
    */
   def start() {
     if (!fileSystem.isDirectory(new Path(logBaseDir))) {
-      throw new IllegalArgumentException(s"Log directory $logBaseDir does not exist.");
+      throw new IllegalArgumentException(s"Log directory $logBaseDir does not exist.")
     }
 
     val workingPath = logPath + IN_PROGRESS