59 lines
1.7 KiB
Python
Executable File
59 lines
1.7 KiB
Python
Executable File
#!/usr/bin/env python
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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.
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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, fcntl, errno
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# Default parallelism is "1" unless overridden on the command-line.
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default="1"
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if len(sys.argv) > 1:
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default=sys.argv[1]
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# Set non-blocking for a given file descriptor.
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def nonblock(fd):
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flags = fcntl.fcntl(fd, fcntl.F_GETFL)
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fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
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return fd
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# Extract and prepare jobserver file descriptors from envirnoment.
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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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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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reader = nonblock(reader)
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except (KeyError, IndexError, ValueError, IOError):
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# Any missing environment strings or bad fds should result in just
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# using the default specified parallelism.
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print(default)
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sys.exit(0)
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# Read out as many jobserver slots as possible.
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jobs = b""
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while True:
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try:
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slot = os.read(reader, 1)
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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 when reach the end of the jobserver queue.
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break
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raise e
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# Return all the reserved slots.
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os.write(writer, jobs)
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# If the jobserver was (impossibly) full or communication failed, use default.
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if len(jobs) < 1:
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print(default)
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# Report available slots (with a bump for our caller's reserveration).
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print(len(jobs) + 1)
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