code: public static RetryContext register(RetryContext context) {
  		RetryContext oldContext = getContext();
  		RetrySynchronizationManager.context.set(context);
  		return oldContext;
  	}
docs: Method for registering a context - should only be used by {@link RetryOperations}
  implementations to ensure that {@link #getContext()} always returns the correct
  value.
  @param context the new context to register
  @return the old context if there was one