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https://issues.jenkins-ci.org/browse/JENKINS-5413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=163670#comment-163670
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Joe Hansche commented on JENKINS-5413:
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[~wolfgang]: by "plugin" you're referring to the clearcase plugin, right? So
that was the issue with your plugin, but not necessarily the issue with the
slaves hanging in general? Although potentially related, I guess?
So if the SCM polling plugin raises a RuntimeException, the slave thread will
die off without notifying the master, and therefore the master continues
waiting for it to finish, even though it never will?
> 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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