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From "Gary Tully (JIRA)" <j...@apache.org>
Subject [jira] Assigned: (AMQ-1956) NPE during broker shutdown when useDatabaseLock="false"
Date Thu, 02 Oct 2008 11:14:52 GMT

     [ https://issues.apache.org/activemq/browse/AMQ-1956?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Gary Tully reassigned AMQ-1956:
-------------------------------

    Assignee: Gary Tully

> NPE during broker shutdown when useDatabaseLock="false"
> -------------------------------------------------------
>
>                 Key: AMQ-1956
>                 URL: https://issues.apache.org/activemq/browse/AMQ-1956
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Message Store
>    Affects Versions: 5.1.0
>            Reporter: Chris Pettitt
>            Assignee: Gary Tully
>         Attachments: BrokerStopFailure.java, NoLockerJDBCPersistenceAdapter.java
>
>
> Steps:
> 1. Create a broker with the persistence adapter set to not use database locking (useDatabaseLock="false")
> 2. Start broker
> 3. Stop broker (but keep the process running, as in a servlet container)
> Result:
> In the logs, I see the following error every 30 seconds:
> 2008/09/25 15:23:55.506 INFO [org.apache.activemq.store.jdbc.JDBCPersistenceAdapter]
No longer able to keep the exclusive lock so giving up being a master
> 2008/09/25 15:23:55.506 WARN [org.apache.activemq.store.jdbc.JDBCPersistenceAdapter]
Failed to stop broker
> 2008/09/25 15:24:25.504 ERROR [org.apache.activemq.store.jdbc.DefaultDatabaseLocker]
Failed to update database lock: java.lang.NullPointerException
> java.lang.NullPointerException
>         at org.apache.activemq.store.jdbc.DefaultDatabaseLocker.keepAlive(DefaultDatabaseLocker.java:102)
>         at org.apache.activemq.store.jdbc.JDBCPersistenceAdapter.databaseLockKeepAlive(JDBCPersistenceAdapter.java:458)
>         at org.apache.activemq.store.jdbc.JDBCPersistenceAdapter$3.run(JDBCPersistenceAdapter.java:260)
>         at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:417)
>         at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:280)
>         at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:135)
>         at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(ScheduledThreadPoolExecutor.java:65)
>         at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.runPeriodic(ScheduledThreadPoolExecutor.java:142)
>         at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:166)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
>         at java.lang.Thread.run(Thread.java:613)
> Analysis:
> During startup, JDBCPersistenceAdapter only initializes the database locker if useDatabaseLock
if true. This is done through lazy initialization by calling getDatabaseLocker (at ~ line
172):
>         if (isUseDatabaseLock()) {
>             DatabaseLocker service = getDatabaseLocker();
>             if (service == null) {
>                 LOG.warn("No databaseLocker configured for the JDBC Persistence Adapter");
>             } else {
>                 service.start();
>             }
>         }
> During shutdown, JDBCPersistenceAdapter calls getDatabaseLocker() to shut it down, but
it does not check if isUseDatabaseLock() is true in this case:
>     public synchronized void stop() throws Exception {
>         if (clockTicket != null) {
>             clockTicket.cancel(true);
>             clockTicket = null;
>         }
>         if (clockDaemon != null) {
>             clockDaemon.shutdown();
>             clockDaemon = null;
>         }
>         DatabaseLocker service = getDatabaseLocker();
>         if (service != null) {
>             service.stop();
>         }
>     }
> This actually causes database locker to be initialized and it subsequently lazy-initializes
an executor to run a task which calls keepAlive(...). The executor threads are set as daemon
threads which prevents this issue from showing up when the lifetime of the process is the
same as the broker. When the broker is deployed in an app server which can outlive the broker
then the above error is logged every 30 seconds.
> I'm attaching one way to solve this problem without having to check everywhere if useDatabaseLock="false".
> Attached:
> BrokerStopFailure.java - sample program that reproduces this bug
> NoLockerJDBCPersistenceAdapter.java - sample extension to JDBCPersistenceAdapter that
fixes this bug

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