Drools KieSession causes memory leak when inserting object to Timer based rule session

Question

We want to use Drools to do a delay job. So, I use timer(int:5s) to do that. However, after I inserted an fact object to the KieSession, the KieSession will start a separated "Thread-XX" to dealt with this delay job, but this thread will never end although the rule has been executed after 5s elapsed.

As a result, if I inserted a large number fact object, for example 100000 objects, there will be 100000 threads in this KieSession, the memory will raise to about 500MB and it will never drop down. The more inserts, the more memory consumed.

I think Drools should close those threads if the object has been evaluated and executed the rule since they're useless.

Is there some option to make those timer thread shutdown after executed? I know drools.halt() in drl file, however, it will halt the whole session rather than each thread in this KieSession.

Here are my code:

1.main class

        KieServices ks = KieServices.Factory.get();
        final KieContainer kContainer = ks.getKieClasspathContainer();
        final KieSessionConfiguration ksconf = ks.newKieSessionConfiguration();
        ksconf.setOption(TimedRuleExectionOption.YES);
        final KieSession kSession = kContainer.newKieSession("ksession-rules", ksconf);

        for (int i = 0; i < 100000; i++) {
            Thread t1 = new Thread(new Runnable() {
                public void run() {
                    Message message = new Message();
                    message.setStatus(Message.HELLO);
                    kSession.insert(message);
                    kSession.fireUntilHalt();
                }
            });

            t1.start();
        }

drl file

    dialect "mvel"
    rule "Hello World"
    timer(int:10s)
       when
          m : Message(m.status == Message.HELLO)
       then
          System.out.println( "no hello"+m.message );
    end

The code above is to share a KieSession. I also try to use one KieSession per fact and then halt and dispose it. However, 100000 KieSession reside in memory at same time will cause 6.7GB memory usage. It's also not acceptable.

So, anyone can help me?

Actually, my business logic is to check if the control point and feedback point are the same within 5mins, otherwise sound an alarm. And there will be about 100000 request at same time. So, is there some other better way to achieve this case by Drools?

Thanks,

To complement on my answer below, the "100000 threads" you are referring to are likely the ones created with your own statement Thread t1 = new Thread(... inside the for loop. — tarilabs
The unfinished thread I referred to is not the thread which I created. I've tested that if I insert the facts in main thread, the memory still accumulates while inserting and never drop down. Maybe the memory cost is not caused by the unfinished thread, that is that what I guess. — capcom923
I also called kSession.retract(item) after sleep 1min. But the memory is still there, no drop down. It's strange what holds the memory. — capcom923

laune laune · Accepted Answer · 2016-11-01T15:22:09

I think that you should not use Drools for scheduling a large number of TimerTasks. You can set up a Timer as a global and call its schedule method as required.

It should be evident that the simple timer attribute cannot cope with the various scenarios that are possible with the API of java.util.Timer and TimerTask. Its primary purpose is to cover simple scenarios for executing something repeatedly as long as a condition prevails. Also, the timer attribute is there so Drools marketing can claim that "you can do it all in Drools, no need to know (much) Java". Bah.

Drools KieSession causes memory leak when inserting object to Timer based rule session

2 Answers