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 .
