1. A grouping method for threads, each thread comprising basic modules and data, the thread being assigned to processors in a program for a multiprocessor system, the program comprising the basic modules and a parallel statement describing relationships between parallel threads for the basic modules, the grouping method comprising: displaying a dataflow graph visually showing a status of each thread based on the parallel statement; and indicating a candidate for a connection of threads on the dataflow graph, wherein the dataflow graph is configured to display data entries, nodes in the basic modules, and edges configured to connect the data entries and the nodes; wherein said displaying and said indicating are implemented by computer hardware.