How to run a task in fixed intervals in a multiple-instances Tomcat env.?

Question

I'm scheduling background task to run in fixed-intervals, but as tomcat is running in multiple instances (i.e. multiple start Apache servers; 3 in my case), then the task runs 3 times in each interval.. I would like it to run once (no matter the number of Tomcat instances running).

I'm running a servlet loaded on startup (in web.xml) which will initiate my task:

<servlet>
    <servlet-name>OnInit</servlet-name>
    <servlet-class>box.OnInit</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

OnInit class initiate single instance of that class:

public class BGTaskRefresh {
    private static BGTaskRefresh refreshTaskFactory = null;
    private final Timer timer = new Timer();

    public BGTaskRefresh() {}
    public static void init()
    {
        if( refreshTaskFactory == null )
        {
            refreshTaskFactory = new BGTaskRefresh();
            refreshTaskFactory.start();
        }
    }

    public void start() 
    {
        timer.schedule(
            new TimerTask() 
            {
                    public void run() 
                    {
                        boxService box = new boxService();
                        box.refreshMethod();
                    } 
                },                      
                5 * 60 * 1000,   // 5-Min Delay for first run
            60 * 60 * 1000); // 60-Mins (Interval between 2 runs)                   
    }
}

score 3 · Answer 1 · edited Aug 18 '19 at 01:07

3

You might want to have a look at quartz-scheduler, especially its clustering capabilities:

_{(source: quartz-scheduler.org)}

This might be an overkill in your situation, but Quartz will take care of running the job on only a single instance (using database for synchronization) and will automatically run the job on an idle server.

Another option is hazelcast and distributed locks and queues it provides.

edited Aug 18 '19 at 01:07

Glorfindel

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answered Mar 05 '12 at 12:39

Tomasz Nurkiewicz

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It seems i (we?) are missing something here. Isn't Java Timer built-in capabilities should be able to handle it? I mean, having fixed-intervals is quite common, and also having your application server run in multiple instances.. – Haim Mar 05 '12 at 12:56
@Haim: how? [`Timer`](http://docs.oracle.com/javase/7/docs/api/java/util/Timer.html) is just a Java class managing few threads. If you have several JVMs (possibly on different machines), how is that class suppose to know about other instances? They are completely independent - that's why your task is executed on each of them and that's why you have answers mentioning Quartz, database and file locking - because you need some sort of synchronization/coordination outside of the JVM. Or am I missing something? – Tomasz Nurkiewicz Mar 05 '12 at 12:59

score 0 · Answer 2 · answered Mar 05 '12 at 12:48

You will need some sort of synchronization mechanism. Although ideally you'd want a distributed scheduler (e.g. Quartz cluster), considering your usage scenario you're likely to have either some mechanism for shared session state or a shared database underlying your application; you can simply record the operation and grab a database-based lock to ensure only one instance will run the command at a time (and double-check after the lock grab to ensure you're not running the same task twice).

Here's one article I've found with a technique for DB-based locking: http://blog.udby.com/archives/15

How to run a task in fixed intervals in a multiple-instances Tomcat env.?

2 Answers2