synchronized block on multiclustered environment(weblogic cluster)

Question

I have a situation where I need to load a list of providers only once . So I have used synchronized block . But it fails in multiclustered environment in weblogic . Is there any way to handle it . This snippet of code works fine in single cluster .

public class AdditionalInfoImplProvider
{
    private volatile boolean isLoaded = false;

    private void ensureProviderLoaded()
    {
        if (!isLoaded) {
            synchronized (this) {
                if (!isLoaded) {
                    // Load Provider
                    isLoaded = true;
                }
            }
        }
    }
}

how about the singleton pattern (but be careful under multi-threading environment) — shahaf, Apr 09 '18 at 10:26
`This works in a single cluster` - what?! This won't even work on a single machine with two JVMs. What do you mean by cluster? — shay__, Apr 09 '18 at 10:41
I mean , weblogic cluster , where we have an admin node and two clusters for the same application — Ankur Adhyapak, Apr 09 '18 at 12:02
What do you mean? Should only a single node of a single cluster load the provider? — Klaimmore, Apr 10 '18 at 19:00
If you explained what "load a list of providers" actually means, precisely, maybe we could provide an advice on how best to do that. — JB Nizet, Apr 10 '18 at 19:02
we are loading some classes in Runtime using : ServiceLoader loader =ServiceLoader.load(AdditionalInfo.class); — Ankur Adhyapak, Apr 12 '18 at 07:24
Is to possible to load the list of providers only once , regardless of the clusters . As of now , its loading in every cluster — Ankur Adhyapak, Apr 12 '18 at 07:26

score 0 · Answer 1 · answered May 24 '18 at 10:51

Java synchronized keyword is a single jvm concept. In a cluster, there are multiple JVMs so all these will synchronize on different AdditionalInfoImplProvider instances and your logic will execute in all Weblogic instances.

As far as I know, this kind of synchronization is not provided in standard JDK.

Singleton design pattern will also not work here because traditionally Singleton means Singleton per JVM & not per cluster.

Primitive way to handle this scenario is to have something external to your application like a lock file or an entry in RDBMS & whosoever gets hold of it first - do the loading & rest simply exit.

You can also have a look if Weblogic provides some kind of listeners on application events - not specific to instances of cluster.

I haven't used Zookeeper but heard people using it for your use case.

Refer this question for broader discussion on the topic.

Summary is , you definitely need something that exists application wide and per JVM constructs wouldn't be sufficient.

score 0 · Answer 2 · answered May 24 '18 at 11:13

WebLogic has a specific interface you should implement - https://docs.oracle.com/cd/E68505_01/wls/WLAPI/weblogic/cluster/singleton/SingletonService.html - when you run the "activate" method this should throw an exception when another instance is already active in your WebLogic cluster.

synchronized block on multiclustered environment(weblogic cluster)

2 Answers2