$ clang++ -o llil4vec-omp -std=c++20 -fopenmp -Wall -O3 llil4vec.cpp -I./fast_io/include

$ time OMP_NUM_THREADS=30 ./llil4vec-omp big?.txt >out.txt

llil4vec (fixed string length=6) start
use OpenMP
get properties      time : 1.07873 secs
sort properties     time : 0.717261 secs
emplace set sort    time : 0.606499 secs
write stdout        time : 0.437287 secs
total               time : 2.83984 secs

real  0m3.201s   <-- total wall time, performs similarly
user  0m45.889s  <-- system fans noticeably louder
sys   0m5.934s