:param ops (list): A list of op.desc to init the task node. (Will be removed in the future)
:param program (Program): An instance of Program to init the task node.
:param lazy_initialize (bool): In user-defined task, the program may change adding feed/fetch op. As efficient consideration, the task node will have the C++ object later.
:param cond_var_name (string): Indicate the cond var name of while.