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https://issues.apache.org/jira/browse/HDFS-2896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14715439#comment-14715439
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Daniel Templeton commented on HDFS-2896:
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The comment in the 2NN that the checkpoint thread should never end has been
removed, presumably as it's no longer relevant. The checkpoint thread is still
a daemon thread, but since the main thread joins on the checkpoint thread, I
don't see where it impacts anything. The 2NN appears to now be consistent with
the NN: in both, the main method launches a thread and then joins it.
Sounds like this JIRA was a causality of HDFS-4426. Anyone against closing it?
> The 2NN incorrectly daemonizes
> ------------------------------
>
> Key: HDFS-2896
> URL: https://issues.apache.org/jira/browse/HDFS-2896
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 0.23.0, 2.0.0-alpha
> Reporter: Eli Collins
> Labels: newbie
>
> The SecondaryNameNode (and Checkpointer) confuse o.a.h.u.Daemon with a Unix
> daemon. Per below it intends to create a thread that never ends, but
> o.a.h.u.Daemon just marks a thread with Java's Thread#setDaemon which means
> Java will terminate the thread when there are no more non-daemon user threads
> running
> {code}
> // Create a never ending deamon
> Daemon checkpointThread = new Daemon(secondary);
> {code}
> Perhaps they thought they were using commons Daemon. We of course don't want
> the 2NN to exit unless it exits itself or is stopped explicitly. Currently it
> won't do this because the main thread is not marked as a daemon thread. In
> any case, let's make the 2NN consistent with the NN in this regard (exit when
> the RPC thread exits).
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