[jira] Resolved: (AMQ-3161) Race condition in ActiveMQ Journal Checkpoint worker thread cleanup leads to multiple running instances

["Gary Tully (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/AMQ-3161?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Gary Tully resolved AMQ-3161.
-----------------------------

       Resolution: Fixed
    Fix Version/s: 5.5.0

patch applied with thanks in r1063710

URL: http://svn.apache.org/viewvc?rev=1063710&view=rev

one minor mod, left unsynced check in store, such that locking overhead occurs only if thread needs a restart.

> Race condition in ActiveMQ Journal Checkpoint worker thread cleanup leads to multiple running instances
> -------------------------------------------------------------------------------------------------------
>
>                 Key: AMQ-3161
>                 URL: https://issues.apache.org/jira/browse/AMQ-3161
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Message Store
>    Affects Versions: 5.4.2
>         Environment: CentOS 5.2
>            Reporter: Craig Condit
>            Assignee: Gary Tully
>            Priority: Critical
>             Fix For: 5.5.0
>
>         Attachments: checkpoint-thread.patch
>
>
> If the ActiveMQ Journal Checkpoint worker thread dies for any reason, any updates to KahaDB trigger the thread to be restarted. Unfortunately, there is a race condition between the Thread.isAlive() check and the restart of the thread, potentially leading to multiple instances of the thread being spawned.  We have observed in a busy environment as many as 8-10 instances of this thread, all waking up every 5 seconds to perform database checkpoints, bringing throughput on the broker to a halt.
> The attached patch adds a lock around access to creation/destruction of this thread and prevents a second instance from being launched inadvertently.

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