This sample shows how a caller workflow can fan out multiple Nexus operations concurrently, take the first result, and cancel the rest using WAIT_REQUESTED cancellation semantics.

With WAIT_REQUESTED, the caller proceeds once the handler has received the cancel request — it does not wait for the handler to finish processing the cancellation.

Start a Temporal server. (See the main samples repo README).

Run the following:

temporal operator namespace create --namespace nexus-cancel-handler-namespace
temporal operator namespace create --namespace nexus-cancel-caller-namespace

temporal operator nexus endpoint create \
  --name nexus-cancel-endpoint \
  --target-namespace nexus-cancel-handler-namespace \
  --target-task-queue nexus-cancel-handler-task-queue

Next, in separate terminal windows:

uv run nexus_cancel/handler/worker.py

uv run nexus_cancel/caller/app.py

On the caller side, you should see a greeting in whichever language completed first:

Hello Nexus 👋

On the handler side, you should see cancellation log messages for the remaining operations:

HelloHandlerWorkflow was cancelled successfully.
HelloHandlerWorkflow was cancelled successfully.
HelloHandlerWorkflow was cancelled successfully.
HelloHandlerWorkflow was cancelled successfully.

The caller workflow returns before all handler workflows have completed their cancellation cleanup. This demonstrates WAIT_REQUESTED semantics: the caller didn't wait for the handler workflows to finish, but still guaranteed that all handlers received the cancellation request.