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- #!/usr/bin/env python
- # SPDX-License-Identifier: GPL-2.0+
- #
- # This determines how many parallel tasks "make" is expecting, as it is
- # not exposed via an special variables, reserves them all, runs a subprocess
- # with PARALLELISM environment variable set, and releases the jobs back again.
- #
- # https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
- from __future__ import print_function
- import os, sys, errno
- import subprocess
- # Extract and prepare jobserver file descriptors from envirnoment.
- claim = 0
- jobs = b""
- try:
- # Fetch the make environment options.
- flags = os.environ['MAKEFLAGS']
- # Look for "--jobserver=R,W"
- # Note that GNU Make has used --jobserver-fds and --jobserver-auth
- # so this handles all of them.
- opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]
- # Parse out R,W file descriptor numbers and set them nonblocking.
- fds = opts[0].split("=", 1)[1]
- reader, writer = [int(x) for x in fds.split(",", 1)]
- # Open a private copy of reader to avoid setting nonblocking
- # on an unexpecting process with the same reader fd.
- reader = os.open("/proc/self/fd/%d" % (reader),
- os.O_RDONLY | os.O_NONBLOCK)
- # Read out as many jobserver slots as possible.
- while True:
- try:
- slot = os.read(reader, 8)
- jobs += slot
- except (OSError, IOError) as e:
- if e.errno == errno.EWOULDBLOCK:
- # Stop at the end of the jobserver queue.
- break
- # If something went wrong, give back the jobs.
- if len(jobs):
- os.write(writer, jobs)
- raise e
- # Add a bump for our caller's reserveration, since we're just going
- # to sit here blocked on our child.
- claim = len(jobs) + 1
- except (KeyError, IndexError, ValueError, OSError, IOError) as e:
- # Any missing environment strings or bad fds should result in just
- # not being parallel.
- pass
- # We can only claim parallelism if there was a jobserver (i.e. a top-level
- # "-jN" argument) and there were no other failures. Otherwise leave out the
- # environment variable and let the child figure out what is best.
- if claim > 0:
- os.environ['PARALLELISM'] = '%d' % (claim)
- rc = subprocess.call(sys.argv[1:])
- # Return all the reserved slots.
- if len(jobs):
- os.write(writer, jobs)
- sys.exit(rc)
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