alibaba/spring-ai-alibaba · warning · UnsupportedOperationException

cancel is not implemented yet!

Error message

cancel is not implemented yet!

What it means

GeneratorPublisher wraps a Generator as a reactive Publisher, but cancellation of the underlying async operation is not yet supported in this library. Calling cancel() unconditionally throws UnsupportedOperationException. It is a placeholder API indicating an unfinished feature.

Source

Thrown at spring-ai-alibaba-graph-core/src/main/java/com/alibaba/cloud/ai/graph/async/internal/reactive/GeneratorPublisher.java:69

			/**
			 * Requests more elements from the upstream Publisher.
			 *
			 * <p>
			 * The Publisher calls this method to indicate that it wants more items. The
			 * parameter {@code n} specifies the number of additional items requested.
			 * @param n the number of items to request, a count greater than zero
			 */
			@Override
			public void request(long n) {
			}

			/**
			 * Cancels the operation.
			 * @throws UnsupportedOperationException if the method is not yet implemented.
			 */
			@Override
			public void cancel() {
				throw new UnsupportedOperationException("cancel is not implemented yet!");
			}
		});

		delegate.forEachAsync(subscriber::onNext).thenAccept(value -> {
			subscriber.onComplete();
		}).exceptionally(ex -> {
			subscriber.onError(ex);
			return null;
		}).join();
	}

}

View on GitHub (pinned to f82da0b50f)

Solutions

1. Do not call cancel(); let the generator run to completion or close the subscription instead
2. Stop consuming the stream (dispose the subscription) and rely on downstream cancellation of forEachAsync
3. Upgrade the library version in case cancellation support has been added
4. Wrap cancel() usage behind a capability check and degrade gracefully when unsupported

Example fix

// before
publisher.cancel();
// after
if (publisher.supportsCancel()) { publisher.cancel(); } else { subscription.dispose(); }

boolean cancelable = !(publisher instanceof GeneratorPublisher);

boolean supportsCancel(Object p) { return !(p instanceof com.alibaba.cloud.ai.graph.async.internal.reactive.GeneratorPublisher); }

try { publisher.cancel(); } catch (UnsupportedOperationException e) { subscription.dispose(); }

When it happens

Trigger: Obtaining the Subscribable/publishable wrapper around a Generator-based async graph stream and invoking its cancel() method (e.g. aborting a streaming run mid-flight).

Common situations: Developers building reactive streaming UIs who try to abort a long-running generator-driven graph execution on user disconnect or timeout.

Related errors

• Currently Spring AI ToolResponseMessage only supports text t
• A2aRemoteAgent has not support schedule.
• LoopAgent must have only one subAgent, please use subAgent()
• Async tool execution failed
• Tool execution was cancelled

AI-assisted analysis of alibaba/spring-ai-alibaba@f82da0b50f (2026-09-09). Data as JSON: /api/errors/006838d60f0a357a. Report an issue: GitHub.