initial multiprocessing eclass

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+# Copyright 1999-2012 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+# $Header: /var/cvsroot/gentoo-x86/eclass/multiprocessing.eclass,v 1.1 2012/06/07 04:59:40 vapier Exp $
+
+# @ECLASS: multiprocessing.eclass
+# @MAINTAINER:
+# base-system@gentoo.org
+# @AUTHOR:
+# Brian Harring <ferringb@gentoo.org>
+# Mike Frysinger <vapier@gentoo.org>
+# @BLURB: parallelization with bash (wtf?)
+# @DESCRIPTION:
+# The multiprocessing eclass contains a suite of functions that allow ebuilds
+# to quickly run things in parallel using shell code.
+#
+# It has two modes: pre-fork and post-fork.  If you don't want to dive into any
+# more nuts & bolts, just use the pre-fork mode.  For main threads that mostly
+# spawn children and then wait for them to finish, use the pre-fork mode.  For
+# main threads that do a bit of processing themselves, use the post-fork mode.
+# You may mix & match them for longer computation loops.
+# @EXAMPLE:
+#
+# @CODE
+# # First initialize things:
+# multijob_init
+#
+# # Then hash a bunch of files in parallel:
+# for n in {0..20} ; do
+# 	multijob_child_init md5sum data.${n} > data.${n}
+# done
+#
+# # Then wait for all the children to finish:
+# multijob_finish
+# @CODE
+
+if [[ ${___ECLASS_ONCE_MULTIPROCESSING} != "recur -_+^+_- spank" ]] ; then
+___ECLASS_ONCE_MULTIPROCESSING="recur -_+^+_- spank"
+
+# @FUNCTION: makeopts_jobs
+# @USAGE: [${MAKEOPTS}]
+# @DESCRIPTION:
+# Searches the arguments (defaults to ${MAKEOPTS}) and extracts the jobs number
+# specified therein.  Useful for running non-make tools in parallel too.
+# i.e. if the user has MAKEOPTS=-j9, this will echo "9" -- we can't return the
+# number as bash normalizes it to [0, 255].  If the flags haven't specified a
+# -j flag, then "1" is shown as that is the default `make` uses.  Since there's
+# no way to represent infinity, we return 999 if the user has -j without a number.
+makeopts_jobs() {
+	[[ $# -eq 0 ]] && set -- ${MAKEOPTS}
+	# This assumes the first .* will be more greedy than the second .*
+	# since POSIX doesn't specify a non-greedy match (i.e. ".*?").
+	local jobs=$(echo " $* " | sed -r -n \
+		-e 's:.*[[:space:]](-j|--jobs[=[:space:]])[[:space:]]*([0-9]+).*:\2:p' \
+		-e 's:.*[[:space:]](-j|--jobs)[[:space:]].*:999:p')
+	echo ${jobs:-1}
+}
+
+# @FUNCTION: multijob_init
+# @USAGE: [${MAKEOPTS}]
+# @DESCRIPTION:
+# Setup the environment for executing code in parallel.
+# You must call this before any other multijob function.
+multijob_init() {
+	# When something goes wrong, try to wait for all the children so we
+	# don't leave any zombies around.
+	has wait ${EBUILD_DEATH_HOOKS} || EBUILD_DEATH_HOOKS+=" wait"
+
+	# Setup a pipe for children to write their pids to when they finish.
+	local pipe="${T}/multijob.pipe"
+	mkfifo "${pipe}"
+	redirect_alloc_fd mj_control_fd "${pipe}"
+	rm -f "${pipe}"
+
+	# See how many children we can fork based on the user's settings.
+	mj_max_jobs=$(makeopts_jobs "$@")
+	mj_num_jobs=0
+}
+
+# @FUNCTION: multijob_child_init
+# @USAGE: [--pre|--post] [command to run in background]
+# @DESCRIPTION:
+# This function has two forms.  You can use it to execute a simple command
+# in the background (and it takes care of everything else), or you must
+# call this first thing in your forked child process.
+#
+# The --pre/--post options allow you to select the child generation mode.
+#
+# @CODE
+# # 1st form: pass the command line as arguments:
+# multijob_child_init ls /dev
+# # Or if you want to use pre/post fork modes:
+# multijob_child_init --pre ls /dev
+# multijob_child_init --post ls /dev
+#
+# # 2nd form: execute multiple stuff in the background (post fork):
+# (
+# multijob_child_init
+# out=`ls`
+# if echo "${out}" | grep foo ; then
+# 	echo "YEAH"
+# fi
+# ) &
+# multijob_post_fork
+#
+# # 2nd form: execute multiple stuff in the background (pre fork):
+# multijob_pre_fork
+# (
+# multijob_child_init
+# out=`ls`
+# if echo "${out}" | grep foo ; then
+# 	echo "YEAH"
+# fi
+# ) &
+# @CODE
+multijob_child_init() {
+	local mode="pre"
+	case $1 in
+	--pre)  mode="pre" ; shift ;;
+	--post) mode="post"; shift ;;
+	esac
+
+	if [[ $# -eq 0 ]] ; then
+		trap 'echo ${BASHPID} $? >&'${mj_control_fd} EXIT
+		trap 'exit 1' INT TERM
+	else
+		local ret
+		[[ ${mode} == "pre" ]] && { multijob_pre_fork; ret=$?; }
+		( multijob_child_init ; "$@" ) &
+		[[ ${mode} == "post" ]] && { multijob_post_fork; ret=$?; }
+		return ${ret}
+	fi
+}
+
+# @FUNCTION: _multijob_fork
+# @INTERNAL
+# @DESCRIPTION:
+# Do the actual book keeping.
+_multijob_fork() {
+	[[ $# -eq 1 ]] || die "incorrect number of arguments"
+
+	local ret=0
+	[[ $1 == "post" ]] && : $(( ++mj_num_jobs ))
+	if [[ ${mj_num_jobs} -ge ${mj_max_jobs} ]] ; then
+		multijob_finish_one
+		ret=$?
+	fi
+	[[ $1 == "pre" ]] && : $(( ++mj_num_jobs ))
+	return ${ret}
+}
+
+# @FUNCTION: multijob_pre_fork
+# @DESCRIPTION:
+# You must call this in the parent process before forking a child process.
+# If the parallel limit has been hit, it will wait for one child to finish
+# and return its exit status.
+multijob_pre_fork() { _multijob_fork pre "$@" ; }
+
+# @FUNCTION: multijob_post_fork
+# @DESCRIPTION:
+# You must call this in the parent process after forking a child process.
+# If the parallel limit has been hit, it will wait for one child to finish
+# and return its exit status.
+multijob_post_fork() { _multijob_fork post "$@" ; }
+
+# @FUNCTION: multijob_finish_one
+# @DESCRIPTION:
+# Wait for a single process to exit and return its exit code.
+multijob_finish_one() {
+	[[ $# -eq 0 ]] || die "${FUNCNAME} takes no arguments"
+
+	local pid ret
+	read -r -u ${mj_control_fd} pid ret || die
+	: $(( --mj_num_jobs ))
+	return ${ret}
+}
+
+# @FUNCTION: multijob_finish
+# @DESCRIPTION:
+# Wait for all pending processes to exit and return the bitwise or
+# of all their exit codes.
+multijob_finish() {
+	local ret=0
+	while [[ ${mj_num_jobs} -gt 0 ]] ; do
+		multijob_finish_one
+		: $(( ret |= $? ))
+	done
+	# Let bash clean up its internal child tracking state.
+	wait
+
+	# Do this after reaping all the children.
+	[[ $# -eq 0 ]] || die "${FUNCNAME} takes no arguments"
+
+	return ${ret}
+}
+
+# @FUNCTION: redirect_alloc_fd
+# @USAGE: <var> <file> [redirection]
+# @DESCRIPTION:
+# Find a free fd and redirect the specified file via it.  Store the new
+# fd in the specified variable.  Useful for the cases where we don't care
+# about the exact fd #.
+redirect_alloc_fd() {
+	local var=$1 file=$2 redir=${3:-"<>"}
+
+	if [[ $(( (BASH_VERSINFO[0] << 8) + BASH_VERSINFO[1] )) -ge $(( (4 << 8) + 1 )) ]] ; then
+		# Newer bash provides this functionality.
+		eval "exec {${var}}${redir}'${file}'"
+	else
+		# Need to provide the functionality ourselves.
+		local fd=10
+		while :; do
+			# Make sure the fd isn't open.  It could be a char device,
+			# or a symlink (possibly broken) to something else.
+			if [[ ! -e /dev/fd/${fd} ]] && [[ ! -L /dev/fd/${fd} ]] ; then
+				eval "exec ${fd}${redir}'${file}'" && break
+			fi
+			[[ ${fd} -gt 1024 ]] && die 'could not locate a free temp fd !?'
+			: $(( ++fd ))
+		done
+		: $(( ${var} = fd ))
+	fi
+}
+
+fi