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From zsxwing <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-6468][Block Manager] Fix the race condi...
Date Tue, 24 Mar 2015 11:04:04 GMT
Github user zsxwing commented on a diff in the pull request:

    https://github.com/apache/spark/pull/5136#discussion_r27018077
  
    --- Diff: core/src/main/scala/org/apache/spark/storage/DiskBlockManager.scala ---
    @@ -91,7 +90,12 @@ private[spark] class DiskBlockManager(blockManager: BlockManager, conf:
SparkCon
       /** List all the files currently stored on disk by the disk manager. */
       def getAllFiles(): Seq[File] = {
         // Get all the files inside the array of array of directories
    -    subDirs.flatten.filter(_ != null).flatMap { dir =>
    +    subDirs.flatMap { dir =>
    --- End diff --
    
    If `a` is not `volatile`,  actually, `a` can be something else. E.g.,
    Thread 1 call `foo`. It creates "foobar" on address 0x1234, then assign 0x1234 to `a`.
However, these update will exist in the current CPU cache, then flush to the memory. It's
possible only `a = 0x1234` has been updated to the memory, but the content in address 0x1234
is still in the current CPU cache. Then Thread 2 may see `a` is  `0x1234` and also see the
old content of address `0x1234`, which is an uninitialized String.
    



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