spark git commit: [SPARK-4714] BlockManager.dropFromMemory() should check whether block has been removed after synchronizing on BlockInfo instance.

[joshrosen]

Repository: spark
Updated Branches:
  refs/heads/master 1f5110630 -> 30dca924d


[SPARK-4714] BlockManager.dropFromMemory() should check whether block has been 
removed after synchronizing on BlockInfo instance.

After synchronizing on the `info` lock in the 
`removeBlock`/`dropOldBlocks`/`dropFromMemory` methods in BlockManager, the 
block that `info` represented may have already removed.

The three methods have the same logic to get the `info` lock:
```
   info = blockInfo.get(id)
   if (info != null) {
     info.synchronized {
       // do something
     }
   }
```

So, there is chance that when a thread enters the `info.synchronized` block, 
`info` has already been removed from the `blockInfo` map by some other thread 
who entered `info.synchronized` first.

The `removeBlock` and `dropOldBlocks` methods are idempotent, so it's safe for 
them to run on blocks that have already been removed.
But in `dropFromMemory` it may be problematic since it may drop block data 
which already removed into the diskstore, and this calls data store operations 
that are not designed to handle missing blocks.

This patch fixes this issue by adding a check to `dropFromMemory` to test 
whether blocks have been removed by a racing thread.

Author: hushan[胡珊] <hus...@xiaomi.com>

Closes #3574 from suyanNone/refine-block-concurrency and squashes the following 
commits:

edb989d [hushan[胡珊]] Refine code style and comments position
55fa4ba [hushan[胡珊]] refine code
e57e270 [hushan[胡珊]] add check info is already remove or not while having 
gotten info.syn


Project: http://git-wip-us.apache.org/repos/asf/spark/repo
Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/30dca924
Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/30dca924
Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/30dca924

Branch: refs/heads/master
Commit: 30dca924df0efbdc1b638fa7c705fe8743570783
Parents: 1f51106
Author: hushan[胡珊] <hus...@xiaomi.com>
Authored: Tue Dec 9 15:11:20 2014 -0800
Committer: Josh Rosen <joshro...@databricks.com>
Committed: Tue Dec 9 15:54:40 2014 -0800

----------------------------------------------------------------------
 core/src/main/scala/org/apache/spark/storage/BlockManager.scala | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/spark/blob/30dca924/core/src/main/scala/org/apache/spark/storage/BlockManager.scala
----------------------------------------------------------------------
diff --git a/core/src/main/scala/org/apache/spark/storage/BlockManager.scala 
b/core/src/main/scala/org/apache/spark/storage/BlockManager.scala
index 308c59e..d7b184f 100644
--- a/core/src/main/scala/org/apache/spark/storage/BlockManager.scala
+++ b/core/src/main/scala/org/apache/spark/storage/BlockManager.scala
@@ -1014,8 +1014,10 @@ private[spark] class BlockManager(
           // If we get here, the block write failed.
           logWarning(s"Block $blockId was marked as failure. Nothing to drop")
           return None
+        } else if (blockInfo.get(blockId).isEmpty) {
+          logWarning(s"Block $blockId was already dropped.")
+          return None
         }
-
         var blockIsUpdated = false
         val level = info.level
 


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