Make bin/BuildPackages.sh compatible with more systems (in particular, ones without wait -n)?

[wilfwilson]

This is a bit of a wish list request, but I thought I'd throw it out there in case anyone wants to work on it.

I only learned of the existence of the --parallel option to bin/BuildPackages.sh (introduced in @ChrisJefferson's PR #3922) because of the in-preparation release notes for GAP 4.11.1. It's great... except that it doesn't work on my computer 🙁. I apparently have an old version of bash, where wait -n gives:

$ wait -n
-bash: wait: -n: invalid option
wait: usage: wait [n]

(A quick Google suggests that wait -n was added in bash 4.3, in 2014).

The comments on #3922 suggest that making something more robust might take a bit of effort, but if anyone has any suggestions for quick and easy fixes, I'm open to your ideas.

[ChrisJefferson]

Can you try replacing the wait -n line with: wait -n 2>&1 >/dev/null || wait. This will reduce the amount of parallelization we do (it will spawn 4 things, then wait for all of them), but will at least still work.

[wilfwilson]

To check, is that command saying "run wait -n, but if that fails, run wait?

I tried the line yesterday with just wait rather than wait -n, and that resulted in about a 45% reduction in time taken (about 5½ minutes to about 3 minutes). It's the same with your suggested line. Thanks. I'll make a PR.

[ChrisJefferson]

Yes, and the 2>&1 >/dev/null hides any error message from wait -n.

If you are curious, wait, means "wait for all background processes to finish running". wait -n means "wait for one background process to finish running". As you say it was added in bash 4.3.