Current File : //usr/lib/python3.6/site-packages/pyudev/_os/pipe.py
# -*- coding: utf-8 -*-
# Copyright (C) 2013 Sebastian Wiesner <lunaryorn@gmail.com>
# This library is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by the
# Free Software Foundation; either version 2.1 of the License, or (at your
# option) any later version.
# This library is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
# for more details.
# You should have received a copy of the GNU Lesser General Public License
# along with this library; if not, write to the Free Software Foundation,
# Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
"""
pyudev._os.pipe
===============
Fallback implementations for pipe.
1. pipe2 from python os module
2. pipe2 from libc
3. pipe from python os module
The Pipe class wraps the chosen implementation.
.. moduleauthor:: Sebastian Wiesner <lunaryorn@gmail.com>
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals
import os
import fcntl
from functools import partial
from pyudev._ctypeslib.libc import fd_pair
from pyudev._ctypeslib.libc import ERROR_CHECKERS
from pyudev._ctypeslib.libc import SIGNATURES
from pyudev._ctypeslib.utils import load_ctypes_library
# Define O_CLOEXEC, if not present in os already
O_CLOEXEC = getattr(os, 'O_CLOEXEC', 0o2000000)
def _pipe2_ctypes(libc, flags):
"""A ``pipe2`` implementation using ``pipe2`` from ctypes.
``libc`` is a :class:`ctypes.CDLL` object for libc. ``flags`` is an
integer providing the flags to ``pipe2``.
Return a pair of file descriptors ``(r, w)``.
"""
fds = fd_pair()
libc.pipe2(fds, flags)
return fds[0], fds[1]
def _pipe2_by_pipe(flags):
"""A ``pipe2`` implementation using :func:`os.pipe`.
``flags`` is an integer providing the flags to ``pipe2``.
.. warning::
This implementation is not atomic!
Return a pair of file descriptors ``(r, w)``.
"""
fds = os.pipe()
if flags & os.O_NONBLOCK != 0:
for fd in fds:
set_fd_status_flag(fd, os.O_NONBLOCK)
if flags & O_CLOEXEC != 0:
for fd in fds:
set_fd_flag(fd, O_CLOEXEC)
return fds
def _get_pipe2_implementation():
"""Find the appropriate implementation for ``pipe2``.
Return a function implementing ``pipe2``."""
if hasattr(os, 'pipe2'):
return os.pipe2 # pylint: disable=no-member
else:
try:
libc = load_ctypes_library("libc", SIGNATURES, ERROR_CHECKERS)
return (partial(_pipe2_ctypes, libc)
if hasattr(libc, 'pipe2') else
_pipe2_by_pipe)
except ImportError:
return _pipe2_by_pipe
_PIPE2 = _get_pipe2_implementation()
def set_fd_flag(fd, flag):
"""Set a flag on a file descriptor.
``fd`` is the file descriptor or file object, ``flag`` the flag as integer.
"""
flags = fcntl.fcntl(fd, fcntl.F_GETFD, 0)
fcntl.fcntl(fd, fcntl.F_SETFD, flags | flag)
def set_fd_status_flag(fd, flag):
"""Set a status flag on a file descriptor.
``fd`` is the file descriptor or file object, ``flag`` the flag as integer.
"""
flags = fcntl.fcntl(fd, fcntl.F_GETFL, 0)
fcntl.fcntl(fd, fcntl.F_SETFL, flags | flag)
class Pipe(object):
"""A unix pipe.
A pipe object provides two file objects: :attr:`source` is a readable file
object, and :attr:`sink` a writeable. Bytes written to :attr:`sink` appear
at :attr:`source`.
Open a pipe with :meth:`open()`.
"""
@classmethod
def open(cls):
"""Open and return a new :class:`Pipe`.
The pipe uses non-blocking IO."""
source, sink = _PIPE2(os.O_NONBLOCK | O_CLOEXEC)
return cls(source, sink)
def __init__(self, source_fd, sink_fd):
"""Create a new pipe object from the given file descriptors.
``source_fd`` is a file descriptor for the readable side of the pipe,
``sink_fd`` is a file descriptor for the writeable side."""
self.source = os.fdopen(source_fd, 'rb', 0)
self.sink = os.fdopen(sink_fd, 'wb', 0)
def close(self):
"""Closes both sides of the pipe."""
try:
self.source.close()
finally:
self.sink.close()
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