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Re: libtool 2.4 args parsing incredibly slow

From: Peter O'Gorman
Subject: Re: libtool 2.4 args parsing incredibly slow
Date: Tue, 25 Jan 2011 21:08:57 -0600
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc13 Thunderbird/3.1.7


Dan reported a libtool performance regression in libtool-2.4 when running his binaries with a large number of arguments.

Libtool creates a shell script which usually sets some env vars and runs the binary, new in recent libtool, the script also takes arguments, so these have to be removed when execing the binary.

Because forking is usually quite expensive, this shell function avoids forks:

func_exec_program ()
  for lt_wr_arg
    case \$lt_wr_arg in
    --lt-*) ;;
    *) set x "$@" "$lt_wr_arg"; shift;;

  func_exec_program_core ${1+"$@"}

Turns out that bash is relatively slow here, even with a simpler loop:

for arg
echo "$@" >/dev/null

$ time bash ./s.sh `seq 1 1000`
real    0m9.866s
user    0m8.104s
sys     0m0.088s

$ time dash ./s.sh `seq 1 1000`
real    0m0.571s
user    0m0.355s
sys     0m0.097s

$ time zsh ./s.sh `seq 1 1000`
real    0m0.770s
user    0m0.541s
sys     0m0.079s

I have not investigated what the other shells are not doing that bash is doing here, it's entirely possible that they're buggy in some way that bash isn't.

We'll try to fix libtool to not cause this problem too, of course.


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