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https://issues.apache.org/jira/browse/HDFS-10742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15433853#comment-15433853
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Chris Douglas commented on HDFS-10742:
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* Is this the intended {{ConcurrentHashMap}} implementation?
{noformat}
+import org.jboss.netty.util.internal.ConcurrentHashMap;
{noformat}
The patch synchronizes on the instance, rather than using {{ConcurrentMap}}
features. The tracking code could be simplified using those methods.
* Some commented code (e.g., {{+ //Thread.dumpStack();}})
* Instead of adding the (unused) {{delay()}} method, consider passing in a
{{org.apache.hadoop.util.Timer}} instance. This would also make it easier to
write the unit test.
* There's a comment explaining the importance of using thread-local storage,
but the current patch neither uses nor requires it.
* Please use the slf4j logger and vararg syntax instead of building strings
that might be discarded/suppressed.
* If the logger is null, shouldn't this fail? The {{Optional}} wrapper seems
unnecessary.
On a related note, the virtues of {{AutoCloseableLock}} (HADOOP-13466) are not
obvious to me. Static analysis tools already catch what it enforces with
{{AutoCloseable}}. Its interface is almost identical to
{{java.util.concurrent.Lock}} (admitting extensions like this). It seems to add
an idiosyncrasy where there is already an idiom (with supporting tooling). Is
there another advantage?
> Measurement of lock held time in FsDatasetImpl
> ----------------------------------------------
>
> Key: HDFS-10742
> URL: https://issues.apache.org/jira/browse/HDFS-10742
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 3.0.0-alpha2
> Reporter: Chen Liang
> Assignee: Chen Liang
> Attachments: HDFS-10742.001.patch, HDFS-10742.002.patch,
> HDFS-10742.003.patch
>
>
> This JIRA proposes to measure the time the of lock of {{FsDatasetImpl}} is
> held by a thread. Doing so will allow us to measure lock statistics.
> This can be done by extending the {{AutoCloseableLock}} lock object in
> {{FsDatasetImpl}}. In the future we can also consider replacing the lock with
> a read-write lock.
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