alibaba/spring-ai-alibaba · error · IllegalStateException

Failed to add next node to queue:

Error message

Failed to add next node to queue: 

What it means

In the same fixpoint traversal, the successor of the current node is re-queued when its reachable-source set changed and it is not yet a full convergence point. A failed queue.offer raises this IllegalStateException — again a defensive check that should never trigger with an unbounded ArrayDeque.

Solutions

1. Verify the official, unmodified release of spring-ai-alibaba-graph-core is in use.
2. Report the issue with the graph topology if reproducible.
3. Rebuild the dependency to rule out artifact corruption.

try { graph.compile(); } catch (IllegalStateException e) { if (e.getMessage().startsWith("Failed to add next node to queue")) { /* rebuild dependency / report bug */ } }

When it happens

Trigger: queue.offer(nextNode) returns false while queueing a successor node during convergence detection — practically impossible for an unbounded ArrayDeque.

Common situations: Not reachable in normal use; signals corrupted or modified library internals.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Failed to add nested convergence node to queue:
• Failed to add start node to queue:
• CreatePluginError
• no generator found!
• SYSTEM_ERROR

AI-assisted analysis of alibaba/spring-ai-alibaba@f82da0b50f (2026-09-09). Data as JSON: /api/errors/71928cd4e320c672. Report an issue: GitHub.

Appendix: source

Thrown at spring-ai-alibaba-graph-core/src/main/java/com/alibaba/cloud/ai/graph/internal/ParallelEdgeProcessor.java:359

			}

			String nextNode = target.id();

			// Update reachability: all sources that reached current also reach nextNode
			Set<String> nextSources = reachableFrom.computeIfAbsent(nextNode, k -> new HashSet<>());
			int sizeBefore = nextSources.size();
			nextSources.addAll(sources);
			boolean sourcesChanged = nextSources.size() > sizeBefore;

			// If this node is reachable from all start nodes, it's the convergence point
			if (nextSources.size() == startNodeIds.size()) {
				return nextNode;
			}

			// Only queue if sources actually changed (prevents infinite loops in cycles)
			if (sourcesChanged && nextSources.size() < startNodeIds.size()) {
				if (!queue.offer(nextNode)) {
					throw new IllegalStateException("Failed to add next node to queue: " + nextNode);
				}
			}
		}

		return null;
	}

	/**
	 * Finds the end of a path starting from the given node.
	 * Follows edges until reaching a node with no outgoing edges or END.
	 */
	private String findPathEnd(String startNode) {
		String current = startNode;
		Set<String> visited = new HashSet<>();

		while (current != null && !visited.contains(current)) {
			visited.add(current);
			Optional<Edge> edgeOpt = processedData.edges().edgeBySourceId(current);

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