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https://issues.apache.org/activemq/browse/AMQ-1956?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gary Tully resolved AMQ-1956.
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Fix Version/s: 5.3.0
Resolution: Fixed
Committed revision 701088.
thanks for the analysis Chris. Since the users of getDatabaseLocker already
check for null i simply return null if a lock is not to be used.
note for future reference: ensure you check the "grant ASF License" check box
when you submit a patch or enhancement, otherwise your contribution cannot be
used. thanks.
> 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
> Fix For: 5.3.0
>
> 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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