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
9 from __future__ import print_function
10 import os, sys, errno
11 import subprocess
12
13 # Extract and prepare jobserver file descriptors from environment.
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 # If the MAKEFLAGS variable contains multiple instances of the
27 # --jobserver-auth= option, the last one is relevant.
28 fds = opts[-1].split("=", 1)[1]
29
30 # Starting with GNU Make 4.4, named pipes are used for reader and writer.
31 # Example argument: --jobserver-auth=fifo:/tmp/GMfifo8134
32 _, _, path = fds.partition('fifo:')
33
34 if path:
35 reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)
36 writer = os.open(path, os.O_WRONLY)
37 else:
38 reader, writer = [int(x) for x in fds.split(",", 1)]
39 # Open a private copy of reader to avoid setting nonblocking
40 # on an unexpecting process with the same reader fd.
41 reader = os.open("/proc/self/fd/%d" % (reader),
42 os.O_RDONLY | os.O_NONBLOCK)
43
44 # Read out as many jobserver slots as possible.
45 while True:
46 try:
47 slot = os.read(reader, 8)
48 jobs += slot
49 except (OSError, IOError) as e:
50 if e.errno == errno.EWOULDBLOCK:
51 # Stop at the end of the jobserver queue.
52 break
53 # If something went wrong, give back the jobs.
54 if len(jobs):
55 os.write(writer, jobs)
56 raise e
57 # Add a bump for our caller's reserveration, since we're just going
58 # to sit here blocked on our child.
59 claim = len(jobs) + 1
60 except (KeyError, IndexError, ValueError, OSError, IOError) as e:
61 # Any missing environment strings or bad fds should result in just
62 # not being parallel.
63 pass
64
65 # We can only claim parallelism if there was a jobserver (i.e. a top-level
66 # "-jN" argument) and there were no other failures. Otherwise leave out the
67 # environment variable and let the child figure out what is best.
68 if claim > 0:
69 os.environ['PARALLELISM'] = '%d' % (claim)
70
71 rc = subprocess.call(sys.argv[1:])
72
73 # Return all the reserved slots.
74 if len(jobs):
75 os.write(writer, jobs)
76
77 sys.exit(rc)
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