LXR linux/scripts/jobserver-exec

   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)
  67