# The MIT License

#

# Copyright (c) 2015-2019 Sebastian Ramacher

#

# Permission is hereby granted, free of charge, to any person obtaining a copy

# of this software and associated documentation files (the "Software"), to deal

# in the Software without restriction, including without limitation the rights

# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

# copies of the Software, and to permit persons to whom the Software is

# furnished to do so, subject to the following conditions:

#

# The above copyright notice and this permission notice shall be included in

# all copies or substantial portions of the Software.

#

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

# THE SOFTWARE.

try:

import fcntl

import errno

has_fcntl = True

except ImportError:

has_fcntl = False

try:

import msvcrt

import os

has_msvcrt = True

except ImportError:

has_msvcrt = False

class BaseLock:

"""Base class for file locking"""

def __init__(self, fileobj, mode=None, filename=None):

self.fileobj = fileobj

self.locked = False

def acquire(self):

pass

def release(self):

pass

def __enter__(self):

self.acquire()

return self

def __exit__(self, *args):

if self.locked:

self.release()

def __del__(self):

if self.locked:

self.release()

class UnixFileLock(BaseLock):

"""Simple file locking for Unix using fcntl"""

def __init__(self, fileobj, mode=None, filename=None):

super().__init__(fileobj)

if mode is None:

mode = fcntl.LOCK_EX

self.mode = mode

def acquire(self):

try:

fcntl.flock(self.fileobj, self.mode)

self.locked = True

except OSError as e:

if e.errno != errno.ENOLCK:

raise e

def release(self):

self.locked = False

fcntl.flock(self.fileobj, fcntl.LOCK_UN)

class WindowsFileLock(BaseLock):

"""Simple file locking for Windows using msvcrt"""

def __init__(self, fileobj, mode=None, filename=None):

super().__init__(None)

self.filename = f"{filename}.lock"

def acquire(self):

# create a lock file and lock it

self.fileobj = os.open(

self.filename, os.O_RDWR | os.O_CREAT | os.O_TRUNC

)

msvcrt.locking(self.fileobj, msvcrt.LK_NBLCK, 1)

self.locked = True

def release(self):

self.locked = False

# unlock lock file and remove it

msvcrt.locking(self.fileobj, msvcrt.LK_UNLCK, 1)

os.close(self.fileobj)

self.fileobj = None

try:

os.remove(self.filename)

except OSError:

pass

if has_fcntl:

FileLock = UnixFileLock

elif has_msvcrt:

FileLock = WindowsFileLock

else:

FileLock = BaseLock

# vim: sw=4 ts=4 sts=4 ai et