reactor-core/src/main/java/reactor/core/publisher/ParallelFlux.java
public final ParallelFlux<T> doOnCancel(Runnable onCancel) {
		Objects.requireNonNull(onCancel, "onCancel");
		return doOnSignal(this, null, null, null, null, null, null, null, onCancel);
	}
public final ParallelFlux<T> doOnCancel(Runnable onCancel) {
		Objects.requireNonNull(onCancel, "onCancel");
		return doOnSignal(this, null, null, null, null, null, null, null, onCancel);
	}
Run the specified runnable when a 'rail' receives a cancellation.

@param onCancel the callback

@return the new {@link ParallelFlux} instance