'Args:
config(TrainConfig): Must contain \'model\' and either one of \'data\' or \'dataflow\'.
scale_gradient (bool): if True, will scale each gradient by ``1.0/nr_gpu``.'

def __init__(self, config, scale_gradient=True):

    apply_prefetch_policy(config)
    self._input_source = config.data
    self._scale_gradient = scale_gradient
    super(AsyncMultiGPUTrainer, self).__init__(config)
