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#!/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-Jobserver
from __future__ import print_function
import os, sys, errno
import subprocess
# Extract and prepare jobserver file descriptors from environment.
claim = 0
jobs = 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]
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) + 1
except (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)
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