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https://issues.apache.org/jira/browse/HDFS-16939?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17696118#comment-17696118
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ASF GitHub Bot commented on HDFS-16939:
---------------------------------------
saxenapranav commented on code in PR #5450:
URL: https://github.com/apache/hadoop/pull/5450#discussion_r1124189602
##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/LowRedundancyBlocks.java:
##########
@@ -369,7 +369,7 @@ synchronized boolean remove(BlockInfo block,
* @return true if the block was found and removed from one of the priority
* queues
*/
- boolean remove(BlockInfo block, int priLevel) {
+ synchronized boolean remove(BlockInfo block, int priLevel) {
Review Comment:
This will just ensure only one thread getting into the remove method. But
what if there is one thread trying to remove, other trying to add or size(). I
feel following should help:
```
private Object syncOnBlockInfoSet(int priority, BlockInfo blockInfo, String
operation) {
LightWeightLinkedSet<BlockInfo> blockInfos
=priorityQueues.get(priority);
synchronized (blockInfos) {
if("size".equalsIgnoreCase(operation)) {
return blockInfos.size();
}
if("remove".equalsIgnoreCase(operation)) {
return blockInfos.remove(blockInfo);
}
//implement other required methods.
else {
return null;
}
}
}
```
all code-pieces where we do operation on an element in `priorityQueues`, we
call `syncOnBlockInfoSet` to do that operation. for ex:
`size=syncOnBlockInfoSet(priority, null, "size")`
> Fix the thread safety bug in LowRedundancyBlocks
> ------------------------------------------------
>
> Key: HDFS-16939
> URL: https://issues.apache.org/jira/browse/HDFS-16939
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namanode
> Reporter: Shuyan Zhang
> Assignee: Shuyan Zhang
> Priority: Major
> Labels: pull-request-available
>
> The remove method in LowRedundancyBlocks is not protected by synchronized.
> This method is private and is called by BlockManager. As a result,
> priorityQueues has the risk of being accessed concurrently by multiple
> threads.
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