Github user li-zhihui commented on a diff in the pull request:
https://github.com/apache/spark/pull/1616#discussion_r17524670
--- Diff: core/src/main/scala/org/apache/spark/util/Utils.scala ---
@@ -313,15 +313,84 @@ 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 = s"${url.hashCode}${timestamp}_cache"
+ val lockFileName = s"${url.hashCode}${timestamp}_lock"
+ val localDir = new File(getLocalDir(conf))
+ val lockFile = new File(localDir, lockFileName)
+ val raf = new RandomAccessFile(lockFile, "rw")
+ // 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()) {
+ doFetchFile(url, localDir, cachedFileName, conf, securityMgr,
hadoopConf)
+ }
+ } finally {
+ lock.release()
+ }
+ if (targetFile.exists && !Files.equal(cachedFile, targetFile)) {
+ if (conf.getBoolean("spark.files.overwrite", false)) {
+ targetFile.delete()
+ logInfo(("File %s exists and does not match contents of %s, " +
+ "replacing it with %s").format(targetFile, url, url))
+ } else {
+ throw new SparkException(
+ "File " + targetFile + " exists and does not match contents
of" + " " + url)
--- End diff --
thanks, done.
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