jobserver-exec (2213B)
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 fds = opts[0].split("=", 1)[1] 27 reader, writer = [int(x) for x in fds.split(",", 1)] 28 # Open a private copy of reader to avoid setting nonblocking 29 # on an unexpecting process with the same reader fd. 30 reader = os.open("/proc/self/fd/%d" % (reader), 31 os.O_RDONLY | os.O_NONBLOCK) 32 33 # Read out as many jobserver slots as possible. 34 while True: 35 try: 36 slot = os.read(reader, 8) 37 jobs += slot 38 except (OSError, IOError) as e: 39 if e.errno == errno.EWOULDBLOCK: 40 # Stop at the end of the jobserver queue. 41 break 42 # If something went wrong, give back the jobs. 43 if len(jobs): 44 os.write(writer, jobs) 45 raise e 46 # Add a bump for our caller's reserveration, since we're just going 47 # to sit here blocked on our child. 48 claim = len(jobs) + 1 49except (KeyError, IndexError, ValueError, OSError, IOError) as e: 50 # Any missing environment strings or bad fds should result in just 51 # not being parallel. 52 pass 53 54# We can only claim parallelism if there was a jobserver (i.e. a top-level 55# "-jN" argument) and there were no other failures. Otherwise leave out the 56# environment variable and let the child figure out what is best. 57if claim > 0: 58 os.environ['PARALLELISM'] = '%d' % (claim) 59 60rc = subprocess.call(sys.argv[1:]) 61 62# Return all the reserved slots. 63if len(jobs): 64 os.write(writer, jobs) 65 66sys.exit(rc)