Re: wait unblocks before signals processed

[Dan Douglas]

Hi Elliott. The behavior of wait differs depending upon whether you are in 
POSIX mode. Try this script, which I think does essentially what you're after 
(also here: https://gist.github.com/3911059 ):

#!/usr/bin/env bash

${BASH_VERSION+shopt -s lastpipe extglob}

if [[ -v .sh.version ]]; then
    builtin getconf
    function BASHPID.get {
        read -r .sh.value _ </proc/self/stat
    }
fi

function f {
    printf '%d: sleeping %d sec\n' "${@:1:2}" >&2
    sleep "$2"

    printf '%d: returning %d\n' "$1" "$3" >&2
    return "$3"
}

function main {
    typeset -i n= j= maxj=$(getconf _NPROCESSORS_ONLN)

    set -m
    trap '((j--))' CHLD

    while ((n++<30)); do
        f "$BASHPID" $(((RANDOM%5)+1)) $((RANDOM%2)) &
        ((++j >= maxj)) && POSIXLY_CORRECT= wait
    done

    echo 'finished, waiting for remaining jobs...' >&2
    wait
}

main "$@"
echo

# vim: set fenc=utf-8 ff=unix ts=4 sts=4 sw=4 ft=sh nowrap et:


The remaining issues are making it work in other shells (Bash in non-POSIX 
mode agrees with ksh, but ksh doesn't agree with POSIX), and also I can't 
think of a reasonable way to retrieve the exit statuses. The status of "wait" 
is rather useless here. Otherwise I think this is the best approach, using 
SIGCHLD and relying upon the POSIX wait behavior. See here: 
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_11

An issue to be aware of is that the trap will fire when any child exits 
including command/process substitutions or pipelines etc. If any are located 
within the main loop then monitor mode needs to be toggled off around them.
-- 
Dan Douglas

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