Tomcat - WELD workaround for asynchronous requests

Question

I have a REST application implemented with WELD 3.0.5 and RestEasy 3.6.1 running on Tomcat 9.

For the asynchronous requests, Tomcat fires the request destroyed event in a different thread than the one that fired the initialized event. In this case, WELD, which uses ThreadLocals, does not deactivate the request context and, as a result, the bean disposal methods are not called.

See: What do WELD-000225, WELD-000335 and WELD-000715 warnings mean?

and Tomcat Bug 57314

My application depends on the container lifecycle events to close resources and clean up, so I need a way to make everything work for async requests as well. The solution I came up with is to add a WebFilter that invalidates the current request context at the end of the execution chain.

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws Exception {

    BeanManager beanManager = CDI.current().getBeanManager();
    AlterableContext context = (AlterableContext) beanManager.getContext(RequestScoped.class);
    try {
        chain.doFilter(request, response);
    } finally {
        if (request.isAsyncStarted()) {
            AbstractBoundContext<?> ctxt = (AbstractBoundContext<?>) delegate;
            ctxt.invalidate();
            ctxt.deactivate();
            ctxt.cleanup();
        }
    }
}

That does a pretty good job discarding the beans and removing some of the thread-local variables. Unfortunately some of the variables remain tied to the pooled thread and Tomcat complains about it:

SEVERE: The web application [cdi-weld] created a ThreadLocal with key of type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal@3d97cd8b]) and a value of type [org.jboss.weld.module.web.servlet.HttpContextLifecycle.Counter] (value [org.jboss.weld.module.web.servlet.HttpContextLifecycle$Counter@43a15b16]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
Nov 02, 2018 10:43:55 AM org.apache.catalina.loader.WebappClassLoaderBase checkThreadLocalMapForLeaks
SEVERE: The web application [cdi-weld] created a ThreadLocal with key of type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal@21d33dd8]) and a value of type [org.jboss.weld.contexts.AbstractManagedContext.ManagedState] (value [org.jboss.weld.contexts.AbstractManagedContext$ManagedState@2a336421]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
Nov 02, 2018 10:43:55 AM org.apache.catalina.loader.WebappClassLoaderBase checkThreadLocalMapForLeaks
SEVERE: The web application [cdi-weld] created a ThreadLocal with key of type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal@294b0f79]) and a value of type [org.jboss.weld.module.web.servlet.ConversationContextActivator$$Lambda$555/1676983761] (value [org.jboss.weld.module.web.servlet.ConversationContextActivator$$Lambda$555/1676983761@60fb88ad]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.

My understanding is that the ThreadLocals get overwritten for each request so that's not exactly a memory leak, but I am still not 100% happy with this solution.

Does anyone know a better way to work around this problem?

score 1 · Answer 1 · answered Nov 05 '18 at 15:34

The below information is not a solution I have tried, but it is my best shot at how you could remedy some of it.

org.jboss.weld.module.web.servlet.HttpContextLifecycle.Counter you probably won't be able to fix, or at least I don't know how.

But the other two are different contexts and you might be able to address it by deactivating them like you did with request context.

org.jboss.weld.contexts.AbstractManagedContext.ManagedState You will have to dig into what context this actually is. Session or conversation is my guess. Try using BeanManager to retrieve contexts for scopes you know are there and see. A little bit of debug goes a long way.

org.jboss.weld.module.web.servlet.ConversationContextActivator$$Lambda$555/1676983761 This should be conversation context (probably LazyHttpConversationContextImpl). Releasing that context could make this go away.

You're right. If I cleanup the Session and Conversation contexts I get rid of most of the thread locals. In the end I'm left only with the Counter. I was hoping there was a better fix. — b0gusb, Nov 07 '18 at 14:53
Well, Weld cannot do much for you there since it is servlet-agnostic and doesn't know Tomcat. Besides IMO it's Tomcat doing it wrong here... — Siliarus, Nov 08 '18 at 16:28

Tomcat - WELD workaround for asynchronous requests

1 Answers1