apache/beam · error

ProcessContinuation must be the final non-error return…

Error message

ProcessContinuation must be the final non-error return parameter

What it means

Sentinel error errProcessContinuationPrecedence from the funcx return-value state machine: in the rsOutput state, a return kind other than the allowed terminal transitions (such as another value after ProcessContinuation was already emitted) was encountered. ProcessContinuation, when returned by a splittable DoFn's ProcessElement, must be the final non-error return value.

Solutions

  1. Reorder returns so ProcessContinuation is the last non-error return value, with error (if any) after it
Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at sdks/go/pkg/beam/core/funcx/fn.go:749 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/9d4e9a624ed252ca. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/core/funcx/fn.go:749

	case FnRTracker:
		return -1, errRTrackerPrecedence
	case FnStateProvider:
		return -1, errStateProviderPrecedence
	case FnTimerProvider:
		return -1, errTimerProviderPrecedence
	case FnIter, FnReIter, FnValue, FnMultiMap:
		return psInput, nil
	case FnEmit:
		return psOutput, nil
	default:
		panic(fmt.Sprintf("library error, unknown ParamKind: %v", transition))
	}
}

var (
	errEventTimeRetPrecedence        = errors.New("beam.EventTime must be first return parameter")
	errErrorPrecedence               = errors.New("error must be the final return parameter")
	errProcessContinuationPrecedence = errors.New("ProcessContinuation must be the final non-error return parameter")
)

type retState int

const (
	rsStart retState = iota
	rsEventTime
	rsOutput
	rsError
	rsProcessContinuation
)

func nextRetState(cur retState, transition ReturnKind) (retState, error) {
	switch cur {
	case rsStart:
		switch transition {
		case RetEventTime:
			return rsEventTime, nil

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