Merging output from parallel blocks on parallel gateway sometimes doesn't work

[DotNetPart]

Describe the bug

I have quite a simple workflow where I split flow into 3 parallel requests and then merge their output in parallel gateway. Sometimes though, my flow hangs and merging doesn't happen though all 3 parallel blocks have finished. I can see that browsing through kogito process instance events.

I went through Kogito code a bit and found a suspicious place. Doesn't this one have a race condition in count updating procedure?

https://github.com/kiegroup/kogito-runtimes/blob/1b2146d259b9119e5fb4e51c422c010199689789/jbpm/jbpm-flow/src/main/java/org/jbpm/workflow/instance/node/JoinInstance.java#L71

Expected behavior

No response

Actual behavior

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How to Reproduce?

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Output of uname -a or ver

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Output of java -version

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GraalVM version (if different from Java)

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Kogito version or git rev (or at least Quarkus version if you are using Kogito via Quarkus platform BOM)

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Build tool (ie. output of mvnw --version or gradlew --version)

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Additional information

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[radtriste]

@ricardozanini @fjtirado any idea ?

[dfiai]

Hello, I have a similar issue. Additionally, when I have several identical BPMN process pods, I encounter a problem where processes with parallel actions freeze.

[dfiai]

@ricardozanini, @fjtirado what are your thoughts on this(but it still won't work with several pods):

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;

private ConcurrentHashMap<Long, AtomicInteger> triggers = new ConcurrentHashMap<>();
...
case Join.TYPE_AND:
    // Use computeIfAbsent to handle the initialization and increment atomically
    triggers.computeIfAbsent(from.getNodeId(), k -> new AtomicInteger(0)).incrementAndGet();

    if (checkAllActivated()) {
        decreaseAllTriggers();
        triggerCompleted();
    }
    break;

[fjtirado]

@dfiai Please go ahead opening a PR with that fix Certainly it would still fail when using multi pod, but at least we avoid the race condition while single pod. Good catch!

[fjtirado]

@dfiai If you have issues opening the PR, let me know and I will do myself, but I believe you deserve the credit on pursuing this together with @DotNetPart

[dfiai]

@fjtirado, sure I'll try it by myself first.