Just make sure $num is set, otherwise it tries to do everything it can at once. I found out the hard way compiling gcc last week, system was unresponsive so I reset, but I'm curious if it would have worked eventually.

This is a pet peeve I have had for a while now. I still have a definition for MAKEFLAGS (with -j [# of cpus-1]) in my profile and rc files and had to learn that if you allow make to start too many things at once, the whole machine would hang. Even switching to a different TTY took ages.

To me, it sounds like a tremendous scheduling issue if a build job can drown a whole system like that. Shouldn't there be some emphasis on non-waiting threads/processes that haven't done much over those who have hogged the CPU in the past without me having to manually adjust the niceness of every build task?

I can’t offer specifics, but it’s probably at the point that you’d compile a different scheduler?

IIRC make -j is equivalent to make -j256...

From the man page:

> If the -j option is given without an argument, make will not limit the number of jobs that can run simultaneously.

Although other implementations might be different of course.

It's not a notion that I carried into my implementation of redo, for example.

    % redo --jobs
    redo: ERROR: jobs: missing option argument
    %

What made you go with that rather than trying to pick a sensible default like the number of cores available? Or was it just a general goal to require explicitness?

It was simplicity, of design, implementation, use, and indeed explanation. There's only one default, the default if the --jobs option is not used; rather than there being two defaults, one for not having the option and another for having the option but not the option argument.

More generally, I try to avoid optional arguments to command options, in line with the guideline in the Single Unix Specification. (I actually picked such ideas up many years ago, before the first POSIX specification, from a book by Eric Foxley titled Unix for Super Users, where there was an appendix on command line option syntax.)

* http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_...

Of course, if the user wants to use the number of cores available, then xe can work that number out and pass it as an argument; and indeed I have done that very thing in some of the package/make scripts that I have published.