[PATCH] Enable parallelism in git submodule update.

[szager@google.com]

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