1#!/usr/bin/env python3 2# SPDX-License-Identifier: GPL-2.0+ 3# 4# This determines how many parallel tasks "make" is expecting, as it is 5# not exposed via an special variables, reserves them all, runs a subprocess 6# with PARALLELISM environment variable set, and releases the jobs back again. 7# 8# https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver 9from __future__ import print_function 10import os, sys, errno 11import subprocess 12 13# Extract and prepare jobserver file descriptors from environment. 14claim = 0 15jobs = b"" 16try: 17 # Fetch the make environment options. 18 flags = os.environ['MAKEFLAGS'] 19 20 # Look for "--jobserver=R,W" 21 # Note that GNU Make has used --jobserver-fds and --jobserver-auth 22 # so this handles all of them. 23 opts = [x for x in flags.split(" ") if x.startswith("--jobserver")] 24 25 # Parse out R,W file descriptor numbers and set them nonblocking. 26 # If the MAKEFLAGS variable contains multiple instances of the 27 # --jobserver-auth= option, the last one is relevant. 28 fds = opts[-1].split("=", 1)[1] 29 reader, writer = [int(x) for x in fds.split(",", 1)] 30 # Open a private copy of reader to avoid setting nonblocking 31 # on an unexpecting process with the same reader fd. 32 reader = os.open("/proc/self/fd/%d" % (reader), 33 os.O_RDONLY | os.O_NONBLOCK) 34 35 # Read out as many jobserver slots as possible. 36 while True: 37 try: 38 slot = os.read(reader, 8) 39 jobs += slot 40 except (OSError, IOError) as e: 41 if e.errno == errno.EWOULDBLOCK: 42 # Stop at the end of the jobserver queue. 43 break 44 # If something went wrong, give back the jobs. 45 if len(jobs): 46 os.write(writer, jobs) 47 raise e 48 # Add a bump for our caller's reserveration, since we're just going 49 # to sit here blocked on our child. 50 claim = len(jobs) + 1 51except (KeyError, IndexError, ValueError, OSError, IOError) as e: 52 # Any missing environment strings or bad fds should result in just 53 # not being parallel. 54 pass 55 56# We can only claim parallelism if there was a jobserver (i.e. a top-level 57# "-jN" argument) and there were no other failures. Otherwise leave out the 58# environment variable and let the child figure out what is best. 59if claim > 0: 60 os.environ['PARALLELISM'] = '%d' % (claim) 61 62rc = subprocess.call(sys.argv[1:]) 63 64# Return all the reserved slots. 65if len(jobs): 66 os.write(writer, jobs) 67 68sys.exit(rc) 69