> and it takes microseconds to launch a subprocess On my laptop (ASUS GA503QM, 5800HS), running /usr/bin/true to completion takes around 400μs, demonstrated by

> and it takes microseconds to launch a subprocess On my laptop (ASUS GA503QM, 5800HS), running /usr/bin/true to completion takes around 400μs, demonstrated by these three different approaches to spawning a thousand processes: $ python -m timeit -n 1000 --setup 'import subprocess' 'subprocess.run(["/usr/bin/true"])' 1000 loops, best of 5: 441 usec per loop $ rustc -o x - <<<'fn main() { for _ in 0..1000 { let _ = std::process::Command::new("/usr/bin/true").status(); } }' && time ./x ./x 0.33s user 0.07s system 99% cpu 0.402 total $ time (i=0; while [ $i -lt 1000 ]; do i=$(($i + 1)); /usr/bin/true; done) [elided] 0.66s user 0.43s system 100% cpu 1.088 total Historically spawning processes was vastly slower on Windows; I’m not certain of the current state though I think it improved a few years ago, but I believe it’s still considerably more than one millisecond; 10–20ms is the vague number that’s lodged in my memory, but not supported, and I can’t test it now. (I invite anyone running Windows to provide figures. You may well already have a true.exe somewhere, or there’s https://github.com/mlocati/true-for-windows https://github.com/mlocati/true-for-windows, or just write your own stub executable.) If you’re going to be using such calls often, spawning just one persistent process and using IPC for I/O is likely to be much faster.