It's `fork` in particular which is much slower. It has to fiddle with Mach port rights, doesn't do overcommit, etc. And autotools is very fork heavy. Apple pro

It's `fork` in particular which is much slower. It has to fiddle with Mach port rights, doesn't do overcommit, etc. And autotools is very fork heavy. Apple provides posix_spawn which is much much faster. Running /usr/bin/false 1000 times in the fish shell is nearly twice as fast (2.25s to 1.25s) when using posix_spawn instead of fork, on the Mac. Autotools doesn't use posix_spawn because there's no benefit on Linux, but it is what Apple's frameworks use internally for process launching.