Github user andrewor14 commented on a diff in the pull request:

    https://github.com/apache/spark/pull/1616#discussion_r17188080
  
    --- Diff: core/src/main/scala/org/apache/spark/util/Utils.scala ---
    @@ -313,14 +313,74 @@ private[spark] object Utils extends Logging {
       }
     
       /**
    +   * Download a file requested by the executor . Supports fetching the 
file in a variety of ways,
    +   * including HTTP, HDFS and files on a standard filesystem, based on the 
URL parameter.
    +   *
    +   * If `useCache` is true, first attempts to fetch the file from a local 
cache that's shared across
    +   * executors running the same application.
    +   *
    +   * Throws SparkException if the target file already exists and has 
different contents than
    +   * the requested file.
    +   */
    +  def fetchFile(
    +      url: String,
    +      targetDir: File,
    +      conf: SparkConf,
    +      securityMgr: SecurityManager,
    +      hadoopConf: Configuration,
    +      timestamp: Long,
    +      useCache: Boolean) {
    +    val fileName = url.split("/").last
    +    val targetFile = new File(targetDir, fileName)
    +    if (useCache) {
    +      val cachedFileName = url.hashCode + timestamp + "_cach"
    +      val lockFileName = url.hashCode + timestamp + "_lock"
    +      val localDir = new File(getLocalDir(conf))
    +      val lockFile = new File(localDir, lockFileName)
    --- End diff --
    
    Why do we need a lock file? This seems a little expensive


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