From 2ffd7424384fc7dee594b00528e8991622ffbb45 Mon Sep 17 00:00:00 2001
From: Li Zhihui <zhihui.li@intel.com>
Date: Mon, 4 Aug 2014 17:29:06 +0800
Subject: [PATCH] add comment for FileLock

---
 core/src/main/scala/org/apache/spark/util/Utils.scala | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/core/src/main/scala/org/apache/spark/util/Utils.scala b/core/src/main/scala/org/apache/spark/util/Utils.scala
index 67e5636689f57..5105bede24c35 100644
--- a/core/src/main/scala/org/apache/spark/util/Utils.scala
+++ b/core/src/main/scala/org/apache/spark/util/Utils.scala
@@ -324,7 +324,10 @@ private[spark] object Utils extends Logging {
     val localDir = new File(getLocalDir(conf))
     val lockFile = new File(localDir, lockFileName)
     val raf = new RandomAccessFile(lockFile, "rw")
-    val lock = raf.getChannel().lock() // only one executor entry
+    // Only one executor entry.
+    // The FileLock is only used to control synchronization for executors download file,
+    // it's always safe regardless of lock type(mandatory or advisory).
+    val lock = raf.getChannel().lock()
     val cachedFile = new File(localDir, cachedFileName)
     try {
       if (!cachedFile.exists()) {