Using flags in new-style QGIS Processing Algorithms

In QGIS 3.6+, there are two different ways to construct a Processing Algorithm.

1. Defining a class inherited from QgsProcessingAlgorithm. In this case, I can define flags for an algorithm as follows:

   class ExampleProcessingAlgorithm(QgsProcessingAlgorithm):    
       ....    
   
       def flags(self):
           return super().flags() | QgsProcessingAlgorithm.FlagNoThreading
       ....
   

2. Using @alg decorator.

   @alg(name='algorithm_name', ...
   @alg.input(type=alg.SOURCE, ...
   @alg.output(type=alg.NUMBER, ...
   
   def algorithm_name(instance, parameters, context, feedback, inputs):
       """
       Description of the algorithm.
       """
   
       ...
   

In @alg case, how can I set flags? There is no explanation about this in QGIS Documentation.