quarkusio/quarkus · error · IllegalStateException

Invalid scheduler implementations detected:

Error message

Invalid scheduler implementations detected: 

What it means

When multiple scheduler implementations are discovered (each registered via a SchedulerImplementationBuildItem with a priority), the processor verifies that each implementation name is unique. Duplicate implementation identifiers make the composite/sorted selection ambiguous, so build fails listing the offending build items.

Source

Thrown at extensions/scheduler/deployment/src/main/java/io/quarkus/scheduler/deployment/SchedulerProcessor.java:126

    static final String INVOKER_SUFFIX = "_ScheduledInvoker";
    static final String NESTED_SEPARATOR = "$_";

    @BuildStep
    SchedulerImplementationBuildItem implementation() {
        return new SchedulerImplementationBuildItem(Scheduled.SIMPLE, DotName.createSimple(SimpleScheduler.class), 0);
    }

    @BuildStep
    void compositeScheduler(SchedulerConfig config, List<SchedulerImplementationBuildItem> implementations,
            BuildProducer<AdditionalBeanBuildItem> additionalBeans,
            BuildProducer<DiscoveredImplementationsBuildItem> discoveredImplementations) {
        List<SchedulerImplementationBuildItem> sorted = implementations.stream()
                .sorted(Comparator.comparingInt(SchedulerImplementationBuildItem::getPriority).reversed()).toList();
        Set<String> found = sorted.stream().map(SchedulerImplementationBuildItem::getImplementation)
                .collect(Collectors.toUnmodifiableSet());
        if (found.size() != implementations.size()) {
            throw new IllegalStateException("Invalid scheduler implementations detected: " + implementations);
        }
        DiscoveredImplementationsBuildItem discovered = new DiscoveredImplementationsBuildItem(
                sorted.get(0).getImplementation(), found,
                config.useCompositeScheduler());
        discoveredImplementations.produce(discovered);
        if (implementations.size() > 1 && config.useCompositeScheduler()) {
            // If multiple implementations are needed we have to register the CompositeScheduler, and
            // instruct the extensions that provide an implementation to modify the bean metadata, i.e. add the marker qualifier
            additionalBeans.produce(AdditionalBeanBuildItem.builder()
                    .addBeanClasses(Constituent.class, CompositeScheduler.class).setUnremovable().build());
        }
    }

    @BuildStep
    void transformSchedulerBeans(DiscoveredImplementationsBuildItem discoveredImplementations,
            List<SchedulerImplementationBuildItem> implementations,
            BuildProducer<AnnotationsTransformerBuildItem> transformer) {
        if (discoveredImplementations.isCompositeSchedulerUsed()) {

View on GitHub (pinned to e1c734241f)

Solutions

1. Remove one of the duplicate scheduler extensions/dependencies from the application
2. Ensure your custom @BuildStep produces the SchedulerImplementationBuildItem only once
3. Use a unique implementation name for custom scheduler implementations
4. Check for duplicate/stale jars carrying the same scheduler implementation

Example fix

// before
@BuildStep
void implA(BuildProducer<SchedulerImplementationBuildItem> p) {
  p.produce(new SchedulerImplementationBuildItem("quartz", 5, ...));
}
@BuildStep
void implB(BuildProducer<SchedulerImplementationBuildItem> p) {
  p.produce(new SchedulerImplementationBuildItem("quartz", 5, ...)); // duplicate
}
// after: produce it once, or use a distinct name e.g. "my-scheduler"

Set<String> names = new HashSet<>();
for (SchedulerImplementationBuildItem i : implementations) {
    if (!names.add(i.getImplementation()))
        throw new IllegalStateException("Duplicate scheduler implementation: " + i.getImplementation());
}

try { /* build */ } catch (IllegalStateException e) {
    if (e.getMessage().startsWith("Invalid scheduler implementations")) { /* dedupe build steps */ }
}

When it happens

Trigger: Two extensions (or the same extension registered twice) produce SchedulerImplementationBuildItems with the same implementation name string.

Common situations: Having both quarkus-quartz and a custom scheduler extension exposing the same implementation id; accidentally producing the build item twice in a custom @BuildStep; stale duplicate jars on the classpath.

Related errors

• Something went wrong during parameter type resolution - expe
• Non-static @Scheduled methods may not be declared on abstrac
• Failed to open path tree with root %s
• Dev services for ${request.getName()} requires a startable s
• Name cannot start with '/':${name}

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/eb65cc578251a91f. Report an issue: GitHub.