cleanup() {
    pkill -P $$ || true
    wait || true
}

trap_add() {
    trap_add_cmd=$1; shift || fatal "${FUNCNAME} usage error"
    for trap_add_name in "$@"; do
        trap -- "$(
            extract_trap_cmd() { printf '%s\n' "${3:-}"; }
            eval "extract_trap_cmd $(trap -p "${trap_add_name}")"
            printf '%s\n' "${trap_add_cmd}"
        )" "${trap_add_name}" \
            || fatal "unable to add to trap ${trap_add_name}"
    done
}

declare -f -t trap_add
trap_add 'cleanup' EXIT