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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