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https://issues.apache.org/jira/browse/ACCUMULO-4809?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16365998#comment-16365998
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Christopher Tubbs commented on ACCUMULO-4809:
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[~kturner], should this issue be closed? The PR has been merged.
> Session manager clean up can happen when lock held.
> ---------------------------------------------------
>
> Key: ACCUMULO-4809
> URL: https://issues.apache.org/jira/browse/ACCUMULO-4809
> Project: Accumulo
> Issue Type: Bug
> Affects Versions: 1.7.3, 1.8.1
> Reporter: Keith Turner
> Priority: Critical
> Labels: pull-request-available
> Fix For: 1.7.4, 1.9.0, 2.0.0
>
> Time Spent: 1h 10m
> Remaining Estimate: 0h
>
> While working on [PR #382|https://github.com/apache/accumulo/pull/382] for
> ACCUMULO-4782 I noticed a significant concurrency bug. Before #382 their was
> a single lock for the session manager. The session manager will clean up idle
> sessions. This clean up should happen outside the session manager lock,
> because all tserver read/write operation use the session manger so it should
> be responsive.
> The bug is the following.
> * Both getActiveScansPerTable() and getActiveScans() lock the session
> manager and then lock idleSessions. See [SessionManager line
> 233|https://github.com/apache/accumulo/blob/rel/1.7.3/server/tserver/src/main/java/org/apache/accumulo/tserver/session/SessionManager.java#L233]
>
> * The sweep() method locks idleSessions and does cleanup while this lock is
> held. [See SessionManager
> 200|https://github.com/apache/accumulo/blob/rel/1.7.3/server/tserver/src/main/java/org/apache/accumulo/tserver/session/SessionManager.java#L200]
>
> Therefore it is possible for getActiveScansPerTable() or getActiveScans() to
> lock the session manager and then block trying to lock idleSessions while
> cleanup is happening in sweep(). This will block all access to the session
> manager while cleanup happens.
> The changes in #382 will fix this for 1.9.0 and 2.0.0. However I Am not sure
> about backporting #382 to 1.7. A more targeted fix could be made for 1.7 or
> #382 could be backported.
>
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