[bug#60807] [PATCH v2] tests: reuse am_cv_filesystem_timestamp_resolution

Mike Frysinger wrote:
> Rather than assume such coarse delays, re-use existing logic for
> probing the current filesystem resolution.  This speeds up the
> testsuite significantly.  On my system, it speeds -j1 up quite a
> lot -- by ~30%.  While I didn't gather many samples to produce a
> statistically significant distribution, my runs seem to be fairly
> consistent with the values below with deviations of <1 minute.
>
> [...]
> diff --git a/t/aclocal-no-force.sh b/t/aclocal-no-force.sh
> index 3e0c04d12f18..2e139d75cf74 100644
> --- a/t/aclocal-no-force.sh
> +++ b/t/aclocal-no-force.sh
> @@ -19,6 +19,18 @@
>  
>  . test-init.sh
>  
> +# Automake relies on high resolution timestamps in perl.  If support isn't
> +# available (see lib/Automake/FileUtils.pm), then fallback to coarse sleeps.
> +# The creative quoting is to avoid spuriously triggering a failure in
> +# the maintainer checks.
> +case ${sleep_delay} in
> +0*)
> +  if ! $PERL -e 'use Time::HiRes' 2>/dev/null; then
> +    sleep='sleep ''2'
> +  fi
> +  ;;
> +esac
> +
>  cat >> configure.ac << 'END'
>  SOME_DEFS
>  AC_CONFIG_FILES([sub/Makefile])
>   

I seem to remember being told that "if !" is non-portable.  Is there 
some other mechanism that ensures this is always run with Bash or might 
"if $PERL ... ; then :; else" be a better option for that line?

Also, you could write that Perl command as "$PERL -MTime::HiRes -e 1 
2>/dev/null" and avoid needing any quotes there, although I suspect this 
is simply a matter of style and the comment refers to the quotes when 
setting $sleep.

You could also exploit that || short-circuits in the shell and replace 
the "if" block with " $PERL ... || sleep='sleep ''2' ".  This allows you 
to directly execute a command on a false result and (I think) it is 
portable, too.  (I half-expect someone to correct me on that along the 
lines of "the shell on Obscurix has a bug where || implicitly uses a 
subshell".)


-- Jacob