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Tummy Bunny commented on HDFS-11820: ------------------------------------ I understand that write lock guard concurrency against concurrent write to I/O. But what to be written also needs to be correct. How useful to return successful response if it failed to write things accurately, I would rather it did not succeed so client can retry. > Thread safety in logEdit? > ------------------------- > > Key: HDFS-11820 > URL: https://issues.apache.org/jira/browse/HDFS-11820 > Project: Hadoop HDFS > Issue Type: Bug > Components: hdfs > Reporter: Tummy Bunny > > Hi there, > I am new to Hadoop and trying to understand how things work under the hood by > browsing through some of the codes. > I noticed a potential thread safety issue in in FSEditLog.java in version > 2.7.1 where the following patterns is used (the current trunk also use the > same pattern): > 1. Instance of FSEditLogOp is retrieved from cache for reuse > 2. Set the attributes (e.g. path, timestamp, etc) > 3. Invoke logEdit(*op*). This method has synchronized block in it, but also > has *wait* if auto-sync is scheduled > Now, if I have two almost simultaneous rename operations, right after each is > about to write edit log: > Thread #1 acquired instance of RenameOp, set the attributes, and invoked > logEdit, then it waits because auto-sync is scheduled. > Thread #2 catches up, and acquires same instance of RenameOp, sets > *different* attributes, and invokes logEdit.. It blocks because of > synchronized block inside logEdit(...), but it manages to modify the > attributes of RenameOp. > The second renameOp could end up being logged twice because both renameOps > are actually the same instance. > The fix is to have synchronized(*op*) prior to calling logEdit(*op*) or clone > the op before using it. > I could be wrong. Am I missing something? > Thanks, > Alexander Koentjara -- This message was sent by Atlassian JIRA (v6.3.15#6346) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org