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https://issues.jenkins-ci.org/browse/JENKINS-5413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=158768#comment-158768
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Christian Wolfgang commented on JENKINS-5413:
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I see two branches of this issue:
1) The fact that slaves gets hung(or threads winds up waiting for lengthy
polling) and how the master Jenkins instance should handle this, and
2) How to prevent slaves from getting hung.
The initial issue suggests 1), but some of the replies suggests 2).
I guess both are valid issues. Should they be treated as one or should this
issue be split up in two?
> SCM polling on slaves getting hung
> ----------------------------------
>
> Key: JENKINS-5413
> URL: https://issues.jenkins-ci.org/browse/JENKINS-5413
> Project: Jenkins
> Issue Type: Bug
> Components: master-slave
> Affects Versions: current
> Reporter: Dean Yu
> Attachments: hung_scm_pollers_02.PNG, threads.vetted.txt,
> thread_dump_02.txt
>
>
> This is to track the problem originally reported here:
> http://n4.nabble.com/Polling-hung-td1310838.html#a1310838
> The referenced thread is relocated to
> http://jenkins.361315.n4.nabble.com/Polling-hung-td1310838.html
> What the problem boils down to is that many remote operations are performed
> synchronously causing the channel object to be locked while a response
> returns. In situations where a lengthy remote operations is using the
> channel, SCM polling can be blocked waiting for the monitor on the channel to
> be released. In extreme situations, all the polling threads can wind up
> waiting on object monitors for the channel objects, preventing further
> processing of polling tasks.
> Furthermore, if the slave dies, the locked channel object still exists in the
> master JVM. If no IOException is thrown to indicate the termination of the
> connection to the pipe, the channel can never be closed because
> Channel.close() itself is a sychronized operation.
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