Re: [PATCH] Enable parallelism in git submodule update.

[Stefan Zager <szager@google.com>]

This is a refresh of a conversation from a couple of months ago.

I didn't try to implement all the desired features (e.g., smart logic
for passing a -j parameter to recursive submodule invocations), but I
did address the one issue that Junio insisted on: the code makes a
best effort to detect whether xargs supports parallel execution on the
host platform, and if it doesn't, then it prints a warning and falls
back to serial execution.

Stefan

On Tue, Oct 30, 2012 at 11:03 AM,  <szager@google.com> wrote:
> The --jobs parameter may be used to set the degree of per-submodule
> parallel execution.
>
> Signed-off-by: Stefan Zager <szager@google.com>
> ---
>  Documentation/git-submodule.txt |    8 ++++++-
>  git-submodule.sh                |   40 ++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 46 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/git-submodule.txt b/Documentation/git-submodule.txt
> index b4683bb..cb23ba7 100644
> --- a/Documentation/git-submodule.txt
> +++ b/Documentation/git-submodule.txt
> @@ -14,7 +14,8 @@ SYNOPSIS
>  'git submodule' [--quiet] status [--cached] [--recursive] [--] [<path>...]
>  'git submodule' [--quiet] init [--] [<path>...]
>  'git submodule' [--quiet] update [--init] [-N|--no-fetch] [--rebase]
> -             [--reference <repository>] [--merge] [--recursive] [--] [<path>...]
> +             [--reference <repository>] [--merge] [--recursive]
> +             [-j|--jobs [jobs]] [--] [<path>...]
>  'git submodule' [--quiet] summary [--cached|--files] [(-n|--summary-limit) <n>]
>               [commit] [--] [<path>...]
>  'git submodule' [--quiet] foreach [--recursive] <command>
> @@ -146,6 +147,11 @@ If the submodule is not yet initialized, and you just want to use the
>  setting as stored in .gitmodules, you can automatically initialize the
>  submodule with the `--init` option.
>  +
> +By default, each submodule is treated serially.  You may specify a degree of
> +parallel execution with the --jobs flag.  If a parameter is provided, it is
> +the maximum number of jobs to run in parallel; without a parameter, all jobs are
> +run in parallel.
> ++
>  If `--recursive` is specified, this command will recurse into the
>  registered submodules, and update any nested submodules within.
>  +
> diff --git a/git-submodule.sh b/git-submodule.sh
> index ab6b110..60a5f96 100755
> --- a/git-submodule.sh
> +++ b/git-submodule.sh
> @@ -8,7 +8,7 @@ dashless=$(basename "$0" | sed -e 's/-/ /')
>  USAGE="[--quiet] add [-b branch] [-f|--force] [--reference <repository>] [--] <repository> [<path>]
>     or: $dashless [--quiet] status [--cached] [--recursive] [--] [<path>...]
>     or: $dashless [--quiet] init [--] [<path>...]
> -   or: $dashless [--quiet] update [--init] [-N|--no-fetch] [-f|--force] [--rebase] [--reference <repository>] [--merge] [--recursive] [--] [<path>...]
> +   or: $dashless [--quiet] update [--init] [-N|--no-fetch] [-f|--force] [--rebase] [--reference <repository>] [--merge] [--recursive] [-j|--jobs [jobs]] [--] [<path>...]
>     or: $dashless [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>...]
>     or: $dashless [--quiet] foreach [--recursive] <command>
>     or: $dashless [--quiet] sync [--] [<path>...]"
> @@ -500,6 +500,7 @@ cmd_update()
>  {
>         # parse $args after "submodule ... update".
>         orig_flags=
> +       jobs="1"
>         while test $# -ne 0
>         do
>                 case "$1" in
> @@ -518,6 +519,20 @@ cmd_update()
>                 -r|--rebase)
>                         update="rebase"
>                         ;;
> +               -j|--jobs)
> +                       case "$2" in
> +                       ''|-*)
> +                               jobs="0"
> +                               ;;
> +                       *)
> +                               jobs="$2"
> +                               shift
> +                               ;;
> +                       esac
> +                       # Don't preserve this arg.
> +                       shift
> +                       continue
> +                       ;;
>                 --reference)
>                         case "$2" in '') usage ;; esac
>                         reference="--reference=$2"
> @@ -551,11 +566,34 @@ cmd_update()
>                 shift
>         done
>
> +       # Correctly handle the case where '-q' came before 'update' on the command line.
> +       if test -n "$GIT_QUIET"
> +       then
> +               orig_flags="$orig_flags -q"
> +       fi
> +
>         if test -n "$init"
>         then
>                 cmd_init "--" "$@" || return
>         fi
>
> +       if test "$jobs" != 1
> +       then
> +               if ( echo test | xargs -P "$jobs" true 2>/dev/null )
> +               then
> +                       if ( echo test | xargs --max-lines=1 true 2>/dev/null ); then
> +                               max_lines="--max-lines=1"
> +                       else
> +                               max_lines="-L 1"
> +                       fi
> +                       module_list "$@" | awk '{print $4}' |
> +                       xargs $max_lines -P "$jobs" git submodule update $orig_flags
> +                       return
> +               else
> +                       echo "Warn: parallel execution is not supported on this platform."
> +               fi
> +       fi
> +
>         cloned_modules=
>         module_list "$@" | {
>         err=
> --
> 1.7.7.3
>