apache/seatunnel · error · IllegalArgumentException

Already an MDCConsumer

Error message

Already an MDCConsumer

What it means

MDCTracer.tracing(context, Consumer) rejects a delegate already wrapped as MDCConsumer with IllegalArgumentException. Double wrapping would capture and restore MDC state twice around a single consumer invocation.

Source

Thrown at seatunnel-api/src/main/java/org/apache/seatunnel/api/tracing/MDCTracer.java:143

    public static MDCScheduledExecutorService tracing(
            MDCContext context, ScheduledExecutorService delegate) {
        if (delegate instanceof MDCExecutor) {
            throw new IllegalArgumentException("Already an MDCExecutor");
        }
        return new MDCScheduledExecutorService(context, delegate);
    }

    public static <T> MDCConsumer<T> tracing(Consumer<T> delegate) {
        return tracing(MDCContext.current(), delegate);
    }

    public static <T> MDCConsumer<T> tracing(Long jobId, Consumer<T> delegate) {
        return tracing(MDCContext.of(jobId), delegate);
    }

    public static <T> MDCConsumer<T> tracing(MDCContext context, Consumer<T> delegate) {
        if (delegate instanceof MDCConsumer) {
            throw new IllegalArgumentException("Already an MDCConsumer");
        }
        return new MDCConsumer<>(context, delegate);
    }

    public static <T, R> MDCFunction<T, R> tracing(Function<T, R> delegate) {
        return tracing(MDCContext.current(), delegate);
    }

    public static <T, R> MDCFunction<T, R> tracing(Long jobId, Function<T, R> delegate) {
        return tracing(MDCContext.of(jobId), delegate);
    }

    public static <T, R> MDCFunction<T, R> tracing(MDCContext context, Function<T, R> delegate) {
        if (delegate instanceof MDCFunction) {
            throw new IllegalArgumentException("Already an MDCFunction");
        }
        return new MDCFunction<>(context, delegate);
    }

View on GitHub (pinned to cf67b549a7)

Solutions

1. Apply tracing at one layer only and pass the MDCConsumer down as-is
2. Guard: `if (c instanceof MDCConsumer) use it else tracing(...)`
3. Remove the redundant tracing call in the inner layer

Example fix

// before
MDCConsumer<T> c = MDCTracer.tracing(jobId, MDCTracer.tracing(jobId, consumer));
// after
MDCConsumer<T> c = MDCTracer.tracing(jobId, consumer);

MDCConsumer<T> safeWrap(Long jobId, Consumer<T> c) {
    return c instanceof MDCConsumer ? (MDCConsumer<T>) c : MDCTracer.tracing(jobId, c);
}

boolean isWrapped(Consumer<?> c) {
    return c instanceof MDCConsumer;
}

try {
    return MDCTracer.tracing(jobId, consumer);
} catch (IllegalArgumentException e) {
    return (MDCConsumer<T>) consumer;
}

When it happens

Trigger: Calling tracing(jobId, consumer) or tracing(context, consumer) where consumer is already an MDCConsumer produced by an earlier tracing() call, e.g. wrapping sink record consumers twice.

Common situations: Sink/committer pipelines where both a generic wrapper and a connector-specific wrapper apply tracing to the same Consumer.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Already an MDCRunnable
• Already an MDCCallable
• Already an MDCExecutor
• Already an MDCFunction
• Already an MDCPredicate

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/d482b89c946e50b5. Report an issue: GitHub.