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66 lines
2.2 KiB
66 lines
2.2 KiB
#!/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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fds = opts[0].split("=", 1)[1] |
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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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