Makeself script slow for large archives in versions 2.4.2+

[tonygoldman]

Use case

I created a makeself archive to flash an Nvidia Jetson.
The makeself size is about 6Gb and contains a Linux filesystem and a flashing script.

Version 2.4.0

Makeself build takes 10 seconds and utilizes all cores simultaniously for compression.

In version 2.4.0 tar is piped directly to the compression program allowing fast and simultanious compression.

exec 3<> "$tmpfile"
( cd "$archdir" && ( tar $TAR_EXTRA -$TAR_ARGS - . | eval "$GZIP_CMD" >&3 ) ) || \
    { echo Aborting: archive directory not found or temporary file: "$tmpfile" could not be created.; exec 3>&-; rm -f "$tmpfile"; exit 1; }
exec 3>&- # try to close the archive

Version 2.4.2 - 2.5.0

Makeself build takes 140 seconds, and only a single core is utilized, except for 10 seconds near the end of the build.

In version 2.4.2+ an empty archive is updated in a loop for each file, unefficient for large archives.
Furthermore, compression only occurs later in the script, removing the advantage of simultanious archiving and compression.

tmparch="${TMPDIR:-/tmp}/mkself$$.tar"
(
    if test "$APPEND" = "y"; then
        tail -n "+$OLDSKIP" "$archname" | eval "$GUNZIP_CMD" > "$tmparch"
    fi
    cd "$archdir"
    # "Determining if a directory is empty"
    # https://www.etalabs.net/sh_tricks.html
    find . \
        \( \
        ! -type d \
        -o \
        \( -links 2 -exec sh -c '
            is_empty () (
                cd "$1"
                set -- .[!.]* ; test -f "$1" && return 1
                set -- ..?* ; test -f "$1" && return 1
                set -- * ; test -f "$1" && return 1
                return 0
            )
            is_empty "$0"' {} \; \
        \) \
        \) -print \
        | LC_ALL=C sort \
        | sed 's/./\\&/g' \
        | xargs $TAR $TAR_EXTRA --format $TAR_FORMAT -$TAR_ARGS "$tmparch"
) || {
    echo "ERROR: failed to create temporary archive: $tmparch"
    rm -f "$tmparch" "$tmpfile"
    exit 1
}

USIZE=`du $DU_ARGS "$tmparch" | awk '{print $1}'`

eval "$GZIP_CMD" <"$tmparch" >"$tmpfile" || {
    echo "ERROR: failed to create temporary file: $tmpfile"
    rm -f "$tmparch" "$tmpfile"
    exit 1
}
rm -f "$tmparch"