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https://issues.apache.org/jira/browse/HDFS-16422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17507969#comment-17507969
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daimin commented on HDFS-16422:
-------------------------------
I tested both NativeRSRawDecoder and RSRawDecoder before, and they seems both
not thread safe to decode, therefore I simply add a synchronized to the decode
method.
In consideration of HADOOP-15499, I will do some more tests to find out what's
missing of the original lock protection.
Thanks for your reminding. [~jingzhao]
> Fix thread safety of EC decoding during concurrent preads
> ---------------------------------------------------------
>
> Key: HDFS-16422
> URL: https://issues.apache.org/jira/browse/HDFS-16422
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: dfsclient, ec, erasure-coding
> Affects Versions: 3.3.0, 3.3.1
> Reporter: daimin
> Assignee: daimin
> Priority: Critical
> Labels: pull-request-available
> Fix For: 3.4.0, 3.2.3, 3.3.3
>
> Time Spent: 3h 40m
> Remaining Estimate: 0h
>
> Reading data on an erasure-coded file with missing replicas(internal block of
> block group) will cause online reconstruction: read dataUnits part of data
> and decode them into the target missing data. Each DFSStripedInputStream
> object has a RawErasureDecoder object, and when we doing pread concurrently,
> RawErasureDecoder.decode will be invoked concurrently too.
> RawErasureDecoder.decode is not thread safe, as a result of that we get wrong
> data from pread occasionally.
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