linux-yocto/scripts/jobserver-exec

#!/usr/bin/env python3

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 environment.

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)