$ time NUM_THREADS=2 ./grep-count-pmap "[aA].*[eE].*[iI].*[oO].*[uU]" /tmp/big.txt
parallel (2) Total Lines: 105000000, Matching Lines: 2195760

N-thds  2           5           10          20          30
real    0m8.113s    0m3.249s    0m1.675s    0m0.958s    0m0.707s
user    0m15.333s   0m15.646s   0m15.809s   0m16.775s   0m18.110s
sys     0m0.840s    0m0.266s    0m0.343s    0m0.489s    0m0.506s