Github user JoshRosen commented on a diff in the pull request: https://github.com/apache/spark/pull/1616#discussion_r17188168 --- 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 -- I think the idea here is that multiple executors JVMs are running on the same machine and we only want to download one copy of the file to the shared cache, so we use a lock file as a form of interprocess synchronization.
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