$ NUM_THREADS=6 ./llil4map big1.txt big2.txt big3.txt >f.tmp
llil4map start
use phmap::parallel_flat_hash_map
use OpenMP
use boost sort
get properties      time : 1.6778 secs
finish merging      time : 0.754921 secs
vector stable sort  time : 0.76791 secs
write stdout        time : 0.382316 secs
total               time : 3.5832 secs