1*4882a593Smuzhiyun#!/usr/bin/env python 2*4882a593Smuzhiyun# SPDX-License-Identifier: GPL-2.0+ 3*4882a593Smuzhiyun# 4*4882a593Smuzhiyun# This determines how many parallel tasks "make" is expecting, as it is 5*4882a593Smuzhiyun# not exposed via an special variables, reserves them all, runs a subprocess 6*4882a593Smuzhiyun# with PARALLELISM environment variable set, and releases the jobs back again. 7*4882a593Smuzhiyun# 8*4882a593Smuzhiyun# https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver 9*4882a593Smuzhiyunfrom __future__ import print_function 10*4882a593Smuzhiyunimport os, sys, errno 11*4882a593Smuzhiyunimport subprocess 12*4882a593Smuzhiyun 13*4882a593Smuzhiyun# Extract and prepare jobserver file descriptors from envirnoment. 14*4882a593Smuzhiyunclaim = 0 15*4882a593Smuzhiyunjobs = b"" 16*4882a593Smuzhiyuntry: 17*4882a593Smuzhiyun # Fetch the make environment options. 18*4882a593Smuzhiyun flags = os.environ['MAKEFLAGS'] 19*4882a593Smuzhiyun 20*4882a593Smuzhiyun # Look for "--jobserver=R,W" 21*4882a593Smuzhiyun # Note that GNU Make has used --jobserver-fds and --jobserver-auth 22*4882a593Smuzhiyun # so this handles all of them. 23*4882a593Smuzhiyun opts = [x for x in flags.split(" ") if x.startswith("--jobserver")] 24*4882a593Smuzhiyun 25*4882a593Smuzhiyun # Parse out R,W file descriptor numbers and set them nonblocking. 26*4882a593Smuzhiyun fds = opts[0].split("=", 1)[1] 27*4882a593Smuzhiyun reader, writer = [int(x) for x in fds.split(",", 1)] 28*4882a593Smuzhiyun # Open a private copy of reader to avoid setting nonblocking 29*4882a593Smuzhiyun # on an unexpecting process with the same reader fd. 30*4882a593Smuzhiyun reader = os.open("/proc/self/fd/%d" % (reader), 31*4882a593Smuzhiyun os.O_RDONLY | os.O_NONBLOCK) 32*4882a593Smuzhiyun 33*4882a593Smuzhiyun # Read out as many jobserver slots as possible. 34*4882a593Smuzhiyun while True: 35*4882a593Smuzhiyun try: 36*4882a593Smuzhiyun slot = os.read(reader, 8) 37*4882a593Smuzhiyun jobs += slot 38*4882a593Smuzhiyun except (OSError, IOError) as e: 39*4882a593Smuzhiyun if e.errno == errno.EWOULDBLOCK: 40*4882a593Smuzhiyun # Stop at the end of the jobserver queue. 41*4882a593Smuzhiyun break 42*4882a593Smuzhiyun # If something went wrong, give back the jobs. 43*4882a593Smuzhiyun if len(jobs): 44*4882a593Smuzhiyun os.write(writer, jobs) 45*4882a593Smuzhiyun raise e 46*4882a593Smuzhiyun # Add a bump for our caller's reserveration, since we're just going 47*4882a593Smuzhiyun # to sit here blocked on our child. 48*4882a593Smuzhiyun claim = len(jobs) + 1 49*4882a593Smuzhiyunexcept (KeyError, IndexError, ValueError, OSError, IOError) as e: 50*4882a593Smuzhiyun # Any missing environment strings or bad fds should result in just 51*4882a593Smuzhiyun # not being parallel. 52*4882a593Smuzhiyun pass 53*4882a593Smuzhiyun 54*4882a593Smuzhiyun# We can only claim parallelism if there was a jobserver (i.e. a top-level 55*4882a593Smuzhiyun# "-jN" argument) and there were no other failures. Otherwise leave out the 56*4882a593Smuzhiyun# environment variable and let the child figure out what is best. 57*4882a593Smuzhiyunif claim > 0: 58*4882a593Smuzhiyun os.environ['PARALLELISM'] = '%d' % (claim) 59*4882a593Smuzhiyun 60*4882a593Smuzhiyunrc = subprocess.call(sys.argv[1:]) 61*4882a593Smuzhiyun 62*4882a593Smuzhiyun# Return all the reserved slots. 63*4882a593Smuzhiyunif len(jobs): 64*4882a593Smuzhiyun os.write(writer, jobs) 65*4882a593Smuzhiyun 66*4882a593Smuzhiyunsys.exit(rc) 67