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 30 # Starting with GNU Make 4.4, named pipes are used for reader and writer. 31 # Example argument: --jobserver-auth=fifo:/tmp/GMfifo8134 32 _, _, path = fds.partition('fifo:') 33 34 if path: 35 reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK) 36 writer = os.open(path, os.O_WRONLY) 37 else: 38 reader, writer = [int(x) for x in fds.split(",", 1)] 39 # Open a private copy of reader to avoid setting nonblocking 40 # on an unexpecting process with the same reader fd. 41 reader = os.open("/proc/self/fd/%d" % (reader), 42 os.O_RDONLY | os.O_NONBLOCK) 43 44 # Read out as many jobserver slots as possible. 45 while True: 46 try: 47 slot = os.read(reader, 8) 48 jobs += slot 49 except (OSError, IOError) as e: 50 if e.errno == errno.EWOULDBLOCK: 51 # Stop at the end of the jobserver queue. 52 break 53 # If something went wrong, give back the jobs. 54 if len(jobs): 55 os.write(writer, jobs) 56 raise e 57 # Add a bump for our caller's reserveration, since we're just going 58 # to sit here blocked on our child. 59 claim = len(jobs) + 1 60except (KeyError, IndexError, ValueError, OSError, IOError) as e: 61 # Any missing environment strings or bad fds should result in just 62 # not being parallel. 63 pass 64 65# We can only claim parallelism if there was a jobserver (i.e. a top-level 66# "-jN" argument) and there were no other failures. Otherwise leave out the 67# environment variable and let the child figure out what is best. 68if claim > 0: 69 os.environ['PARALLELISM'] = '%d' % (claim) 70 71rc = subprocess.call(sys.argv[1:]) 72 73# Return all the reserved slots. 74if len(jobs): 75 os.write(writer, jobs) 76 77sys.exit(rc) 78