scripts/jobserver-exec

   1 #!/usr/bin/env python
   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
   9 from __future__ import print_function
  10 import os, sys, errno
  11 import subprocess
  12
  13 # Extract and prepare jobserver file descriptors from envirnoment.
  14 claim = 0
  15 jobs = b""
  16 try:
  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
  49 except (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.
  57 if claim > 0:
  58         os.environ['PARALLELISM'] = '%d' % (claim)
  59
  60 rc = subprocess.call(sys.argv[1:])
  61
  62 # Return all the reserved slots.
  63 if len(jobs):
  64         os.write(writer, jobs)
  65
  66 sys.exit(rc)