Performance

Call true 256 times, running 4 processes in parallel:

Tool	Version	Time
Para	0.11	0.04 secs
Concurrently	9.1.0	0.13 secs
GNU Parallel	20241022	0.70 secs
rust-parallel	1.18.1	0.04 secs

Times are averages taken from 1,000 runs.

Commands

Create a list of 256 true’s:

cmds=
for _ in $(seq 0 255)
do cmds="${cmds}true "
done

Para:

for _ in $(seq 0 999)
do command time para -j4 -l0 ${cmds:?}
done 2>&1 |
awk 'BEGIN {total=0} {total += $1} END {print (total/NR)}'

Concurrently:

for _ in $(seq 0 999)
do command time concurrently -k -m 4 -r ${cmds:?}
done 2>&1 |
awk 'BEGIN {total=0} {total += $1} END {print (total/NR)}'

GNU Parallel:

for _ in $(seq 0 999)
do command time parallel -j 4 --halt now,fail=1 ::: ${cmds:?}
done 2>&1 |
awk 'BEGIN {total=0} {total += $1} END {print (total/NR)}'

rust-parallel:

for _ in $(seq 0 999)
do command time rust-parallel -j 4 --exit-on-error ::: ${cmds:?}
done 2>&1 |
awk 'BEGIN {total=0} {total += $1} END {print (total/NR)}'