ArrayList is not thread safe. Field timedOutItems is typically protected by synchronization on itself. However, in one place, the field is inside a synchronized on a different object, which does not ensure protection#1030
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anuengineer merged 1 commit intoapache:trunkfrom Jun 28, 2019
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…ted by synchronization on itself. However, in one place, the field is inside a synchronized on a different object, which does not ensure protection.
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…e#1030) * Adding initial implementation for EventHubSystemAdmin. * Code clean up.
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The field
timedOutItems(anArrayList, i.e., not thread safe):https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java#L70
is protected by synchronization on itself (
timedOutItems):https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java#L167-L168
https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java#L267-L268
https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java#L178
However, in one place:
https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/PendingReconstructionBlocks.java#L133-L135
it is (trying to be) protected by synchronized using
pendingReconstructions--- but this cannot protecttimedOutItems.Synchronized on different objects does not ensure mutual exclusion with the other locations.
I.e., 2 code locations, one synchronized by
pendingReconstructionsand the other bytimedOutItemscan still executed concurrently.This CR adds the synchronized on
timedOutItems.Note that this CR keeps the synchronized on
pendingReconstructions, which is needed for a different purpose (protectpendingReconstructions)