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javajsfjsf-2java-8cdi

Accessing CDI SessionScoped bean doesn't work in Java 8 parallel stream

I'm having trouble understanding why this code doesn't work. Basically I want to access a CDI SessionScoped bean from a CDI ViewScoped bean during a parallelStream() function, I get this exception:

WELD-001303: No active contexts for scope type javax.enterprise.context.SessionScoped

This is running in Wildfly 10.1.

The ViewScoped bean:

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import javax.faces.view.ViewScoped;
import javax.inject.Inject;
import javax.inject.Named;

@ViewScoped
@Named
public class TestController implements Serializable {
    private static final long serialVersionUID = 1L;

    @Inject SessionController sessionController;

    public void works() {
        List<Function<String, String>> functions = new ArrayList<>();
        functions.add((String input) -> {
            return sessionController.getSomething();
        });
        functions.add((String input) -> {
            return sessionController.getSomethingElse();
        });
        functions.stream().forEach(f -> f.apply("input"));
    }

    public void doesNotWork() {
        List<Function<String, String>> functions = new ArrayList<>();
        functions.add((String input) -> {
            return sessionController.getSomething();
        });
        functions.add((String input) -> {
            return sessionController.getSomethingElse();
        });
        functions.parallelStream().forEach(f -> f.apply("input"));
    }
}

The SessionScoped bean:

import java.io.Serializable;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;

@Named
@SessionScoped
public class SessionController implements Serializable {
    private static final long serialVersionUID = 1L;

    public String getSomething() {
        return "something";
    }
    public String getSomethingElse() {
        return "else";
    }
}

The XHTML:

<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:p="http://primefaces.org/ui">

    <h:head />

    <h:body>
        <h:form>
            <p:commandButton value="Works" action="#{testController.works}" />
            <br />
            <p:commandButton value="Does Not Work" action="#{testController.doesNotWork}" />
        </h:form>
    </h:body>
</html>

Stacktrace:

Caused by: org.jboss.weld.context.ContextNotActiveException: WELD-001303: No active contexts for scope type javax.enterprise.context.SessionScoped
    at org.jboss.weld.manager.BeanManagerImpl.getContext(BeanManagerImpl.java:689)
    at org.jboss.weld.bean.ContextualInstanceStrategy$DefaultContextualInstanceStrategy.getIfExists(ContextualInstanceStrategy.java:90)
    at org.jboss.weld.bean.ContextualInstanceStrategy$CachingContextualInstanceStrategy.getIfExists(ContextualInstanceStrategy.java:165)
    at org.jboss.weld.bean.ContextualInstance.getIfExists(ContextualInstance.java:63)
    at org.jboss.weld.bean.proxy.ContextBeanInstance.getInstance(ContextBeanInstance.java:83)
    at org.jboss.weld.bean.proxy.ProxyMethodHandler.getInstance(ProxyMethodHandler.java:125)
    at com.SessionController$Proxy$_$$_WeldClientProxy.getSomething(Unknown Source)
    at com.TestController.lambda$3(TestController.java:33)
    at com.TestController.lambda$5(TestController.java:38)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
    at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
    at java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:291)
    at java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:731)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

We have theories that the session may be thread specific, but no hard proof.

Also curious if there's a work-around. The real code is much more complex than this so we can't preload the SessionController results beforehand without losing the benefits of the parallel stream.

Solution

  • What I think you are bumping into is that using parallel streams means you will run in multiple threads. Now, that is a problem with CDI and contexts, because you would need context propagation - e.g. in the main thread you currently have (for instance) session context active, but when you create another thread, it is not active there.

    Chapter 6.3 in spec describes it more in-depth but to give you the short story - context propagation to other threads does not work by default. And there are good reasons for that - it would be very costly (synchronization) and you would need to solve loads of very weird situations such as having one of the threads invalidation session, hence de-activating session context while other threads operate on it. And many more such situations.

    Also, there is no built-in workaround for this. What you could do though, is implementing your own scope, or enhancing existing session scope, but that would be very complicated I guess.