Stop scheduled timer when shutdown tomcat
Solution 1
Do not use Timer
in an Java EE environment! If the task throws a runtime exception, then the whole Timer
is killed and won't run anymore. You basically needs to restart the whole server to get it to run again. Also, it is sensitive to changes in the system clock.
Use ScheduledExecutorService
instead. It's not sensitive to exceptions thrown in tasks nor to changes in system clock. You can shutdown it by its shutdownNow()
method.
Here's an example of how the entire ServletContextListener
implementation can look like (note: no registration in web.xml
required thanks to the new @WebListener
annotation):
@WebListener
public class BackgroundJobManager implements ServletContextListener {
private ScheduledExecutorService scheduler;
@Override
public void contextInitialized(ServletContextEvent event) {
scheduler = Executors.newSingleThreadScheduledExecutor();
scheduler.scheduleAtFixedRate(new YourParsingJob(), 0, 5, TimeUnit.HOUR);
}
@Override
public void contextDestroyed(ServletContextEvent event) {
scheduler.shutdownNow();
}
}
Solution 2
The servlets destroy method is called as the servlet is about to be unloaded. You could cancel the timer from within there, providing that you altered the scope of the parserTimer itself to make it an instance variable. I don't see a problem with that provided that you access it only from within init and destroy.
The servlet engine is free to unload the servlet whenever it sees fit, but in pratice I'm only ever seen it called as the servlet engine is stopped - other people may have other experiences of this though that might prove me wrong.
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Comments
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Derek Li over 3 years
I have a WAR file deployed to Tomcat server, one of the class will get called at start up time, then the init() method will schedule a timer to fire every 5 hours to perform some tasks.
My init() code looks like this:
public void init() { TimerTask parserTimerTask = new TimerTask() { @Override public void run() { XmlParser.parsePage(); } }; Timer parserTimer = new Timer(); parserTimer.scheduleAtFixedRate(parserTimerTask, 0, PERIOD); }
My application runs without problem, but when I shutdown the Tomcat using /etc/init.d/tomcat7 stop, then I check the log (catalina.out) it has a entry like this:
SEVERE: The web application [/MyApplication] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak.
I understand this is caused by me schedule the timer, but my question is:
- I didn't set
setDeamon
to true, so shouldn't the timer prevent Tomcat from shutting down, rather than left running? - Can I, in my application, detect Tomcat is going to be shutdown and cancel my timer?
- What are the other solutions I can use to take care of this issue?
Thanks!
UPDATE
I changed my code to the following based on some search and DaveHowes's answer.
Timer parserTimer; TimerTask parserTimerTask; public void init() { parserTimerTask = new TimerTask() { @Override public void run() { XmlParser.parsePage(); } }; parserTimer = new Timer(); parserTimer.scheduleAtFixedRate(parserTimerTask, 0, PERIOD); } @Override public void contextDestroyed(ServletContextEvent arg0) { Logger logger = Logger.getRootLogger(); logger.info("DETECT TOMCAT SERVER IS GOING TO SHUT DOWN"); logger.info("CANCEL TIMER TASK AND TIMER"); otsParserTimerTask.cancel(); otsParserTimer.cancel(); logger.info("CANCELING COMPLETE"); } @Override public void contextInitialized(ServletContextEvent arg0) { }
Now my new question:
- I cancel TimerTask first then Timer, is this correct?
- Are there other thing I should do?
Thanks!
UPDATE
It doesn't work. I put some logging statement in the contextDestroyed() method, after I shutdown Tomcat, the log file only has the following:
PowderGodAppWebService -> [07 Feb 2012 04:09:46 PM] INFO (PowderGodAppWebService.java:45):: DETECT TOMCAT SERVER IS GOING TO SHUT DOWN PowderGodAppWebService -> [07 Feb 2012 04:09:46 PM] INFO (PowderGodAppWebService.java:46):: CANCEL TIMER TASK AND TIMER
CANCELING COMPLETE is not there.
I also checked processes that are running (I'm not a Linux expert so I just use Mac's Activity Monitor.
- Make sure no java process is running
- Start Tomcat, note the PID of that java process
- Stop Tomcat
- Found the Tomcat process is gone
- Start Tomcat, note the PID of that java process
- Deploy my war file
- Sample the process, see [Timer-0] thread is there
- Shutdown Tomcat
- Found that the process is still there
- Sample the process
- See [Timer-0] is still there
FIXED
I changed my code to
parserTimer = new Timer(true);
so that my timer runs as a daemon thread because thecontextDestroyed()
gets called after Tomcat actually shuts down."All servlets and filters will have been destroyed before any ServletContextListeners are notified of context destruction."
http://docs.oracle.com/javaee/6/api/javax/servlet/ServletContextListener.html
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DaveH over 12 yearsShouldn't those cancels be in contextDestroyed() ?
-
Derek Li over 12 yearsYes... I guess it's time for bed, thanks for pointing out!
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DaveH over 12 yearsTimerTask#cancel won't interrupt the task if it is currently running - it'll just make sure that it'll never run again - but apart from that, I'd say that you'd be fine with that
-
Don Cheadle over 9 yearssince you used
parserTimer = new Timer(true);
does that mean the parser will continue running as a background process even after Tomcat stops? Or does it mean that it blocks Tomcat from stopping until it is finished? I'm in a very similar situation - hoping to reliably shutdown a thread when Tomcat is being stopped, and I'm not sure what works.
- I didn't set
-
Basil Bourque over 10 yearsWow! This answer was amazingly helpful. Thank you very much. For other readers, one point of clarification… The
new YourParsingJob()
should be an instance of the interface Runnable as the JavaDoc explains. -
rekiem87 over 10 yearsAnd what happend if i need access to some resource like an
EntityManager
, can you have acces to this or you have to use@Singleton
with@Startup
anntotation? -
BalusC over 10 years@rekiem87: if you have EJB at hands, use
@Schedule
instead. Examples: stackoverflow.com/a/8482933 and stackoverflow.com/q/7499769 (bottom part). Current question is about Tomcat which doesn't have JPA and EJB. Be careful in finding answers ... -
user1697575 over 9 yearsSmall correction, Tomcat project comes with TomEE for enterprise. It has prepackaged CDI, EJB and JPA. (see openejb.apache.org/apache-tomee.html)
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BalusC over 9 years@user1697575: TomEE !== Tomcat.
-
Basil Bourque about 7 yearsTo clarify, Apache TomEE is a superset of Apache Tomcat, thus the cute choice of name. The idea was to start with Tomcat (for Servlets & JSP, and web server), then add the necessary Java EE related libraries to meet the requirements of the spec for Java EE Web Profile (a subset of full Java EE). As of 2017-05, TomEE 7.0.3 is based on Tomcat 8.5.11. In other words:
( Tomcat + some Java EE components ) = TomEE