Multithread Merge Sorting
"N" is the number of random generated numbers (for testing purposes) The "merge_sort_mt(start, len, 4);" is the line that defines the number of threads. The third attribute, in this case "4" means 4 threads.
Multithreaded applications have overhead, which means the generation of the threads, sync and closure, take time. Therefore this method is to be used only on large enough number sets.