#!/usr/bin/env python3# SPDX-License-Identifier: GPL-2.0+## This determines how many parallel tasks "make" is expecting, as it is# not exposed via an special variables, reserves them all, runs a subprocess# with PARALLELISM environment variable set, and releases the jobs back again.## https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserverfrom __future__ import print_functionimport os, sys, errnoimport subprocess # Extract and prepare jobserver file descriptors from environment.claim = 0jobs = b""try:	# Fetch the make environment options.	flags = os.environ['MAKEFLAGS'] 	# Look for "--jobserver=R,W"	# Note that GNU Make has used --jobserver-fds and --jobserver-auth	# so this handles all of them.	opts = [x for x in flags.split(" ") if x.startswith("--jobserver")] 	# Parse out R,W file descriptor numbers and set them nonblocking.	# If the MAKEFLAGS variable contains multiple instances of the	# --jobserver-auth= option, the last one is relevant.	fds = opts[-1].split("=", 1)[1] 	# Starting with GNU Make 4.4, named pipes are used for reader and writer.	# Example argument: --jobserver-auth=fifo:/tmp/GMfifo8134	_, _, path = fds.partition('fifo:') 	if path:		reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)		writer = os.open(path, os.O_WRONLY)	else:		reader, writer = [int(x) for x in fds.split(",", 1)]		# Open a private copy of reader to avoid setting nonblocking		# on an unexpecting process with the same reader fd.		reader = os.open("/proc/self/fd/%d" % (reader),				 os.O_RDONLY | os.O_NONBLOCK) 	# Read out as many jobserver slots as possible.	while True:		try:			slot = os.read(reader, 8)			jobs += slot		except (OSError, IOError) as e:			if e.errno == errno.EWOULDBLOCK:				# Stop at the end of the jobserver queue.				break			# If something went wrong, give back the jobs.			if len(jobs):				os.write(writer, jobs)			raise e	# Add a bump for our caller's reserveration, since we're just going	# to sit here blocked on our child.	claim = len(jobs) + 1except (KeyError, IndexError, ValueError, OSError, IOError) as e:	# Any missing environment strings or bad fds should result in just	# not being parallel.	pass # We can only claim parallelism if there was a jobserver (i.e. a top-level# "-jN" argument) and there were no other failures. Otherwise leave out the# environment variable and let the child figure out what is best.if claim > 0:	os.environ['PARALLELISM'] = '%d' % (claim) rc = subprocess.call(sys.argv[1:]) # Return all the reserved slots.if len(jobs):	os.write(writer, jobs) sys.exit(rc)