78 lines
2.6 KiB
Plaintext
78 lines
2.6 KiB
Plaintext
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#!/usr/bin/env python3
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# SPDX-License-Identifier: GPL-2.0+
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#
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# This determines how many parallel tasks "make" is expecting, as it is
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# not exposed via an special variables, reserves them all, runs a subprocess
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# with PARALLELISM environment variable set, and releases the jobs back again.
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#
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# https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
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from __future__ import print_function
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import os, sys, errno
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import subprocess
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# Extract and prepare jobserver file descriptors from environment.
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claim = 0
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jobs = b""
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try:
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# Fetch the make environment options.
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flags = os.environ['MAKEFLAGS']
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# Look for "--jobserver=R,W"
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# Note that GNU Make has used --jobserver-fds and --jobserver-auth
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# so this handles all of them.
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opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]
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# Parse out R,W file descriptor numbers and set them nonblocking.
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# If the MAKEFLAGS variable contains multiple instances of the
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# --jobserver-auth= option, the last one is relevant.
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fds = opts[-1].split("=", 1)[1]
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# Starting with GNU Make 4.4, named pipes are used for reader and writer.
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# Example argument: --jobserver-auth=fifo:/tmp/GMfifo8134
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_, _, path = fds.partition('fifo:')
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if path:
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reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)
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writer = os.open(path, os.O_WRONLY)
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else:
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reader, writer = [int(x) for x in fds.split(",", 1)]
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# Open a private copy of reader to avoid setting nonblocking
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# on an unexpecting process with the same reader fd.
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reader = os.open("/proc/self/fd/%d" % (reader),
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os.O_RDONLY | os.O_NONBLOCK)
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# Read out as many jobserver slots as possible.
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while True:
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try:
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slot = os.read(reader, 8)
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jobs += slot
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except (OSError, IOError) as e:
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if e.errno == errno.EWOULDBLOCK:
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# Stop at the end of the jobserver queue.
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break
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# If something went wrong, give back the jobs.
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if len(jobs):
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os.write(writer, jobs)
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raise e
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# Add a bump for our caller's reserveration, since we're just going
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# to sit here blocked on our child.
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claim = len(jobs) + 1
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except (KeyError, IndexError, ValueError, OSError, IOError) as e:
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# Any missing environment strings or bad fds should result in just
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# not being parallel.
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pass
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# We can only claim parallelism if there was a jobserver (i.e. a top-level
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# "-jN" argument) and there were no other failures. Otherwise leave out the
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# environment variable and let the child figure out what is best.
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if claim > 0:
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os.environ['PARALLELISM'] = '%d' % (claim)
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rc = subprocess.call(sys.argv[1:])
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# Return all the reserved slots.
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if len(jobs):
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os.write(writer, jobs)
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sys.exit(rc)
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