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# portalocker.py - Cross-platform (posix/nt) API for flock-style file locking.
# Requires python 1.5.2 or better.
'''Cross-platform (posix/nt) API for flock-style file locking.
Synopsis:
import portalocker
file = open('somefile', 'r+')
portalocker.lock(file, portalocker.LOCK_EX)
file.seek(12)
file.write('foo')
file.close()
If you know what you're doing, you may choose to
portalocker.unlock(file)
before closing the file, but why?
Methods:
lock( file, flags )
unlock( file )
Constants:
LOCK_EX
LOCK_SH
LOCK_NB
Exceptions:
LockException
Notes:
For the 'nt' platform, this module requires the Python Extensions for Windows.
Be aware that this may not work as expected on Windows 95/98/ME.
History:
I learned the win32 technique for locking files from sample code
provided by John Nielsen <nielsenjf@my-deja.com> in the documentation
that accompanies the win32 modules.
Author: Jonathan Feinberg <jdf@pobox.com>,
Lowell Alleman <lalleman@mfps.com>
Version: $Id: portalocker.py 5474 2008-05-16 20:53:50Z lowell $
'''
__all__ = [
'lock',
'unlock',
'LOCK_EX',
'LOCK_SH',
'LOCK_NB',
'LockException',
]
import os
class LockException(Exception):
# Error codes:
LOCK_FAILED = 1
if os.name == 'nt': # pragma: no cover
import win32con
import win32file
import pywintypes
LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
LOCK_SH = 0 # the default
LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
# is there any reason not to reuse the following structure?
__overlapped = pywintypes.OVERLAPPED()
elif os.name == 'posix':
import fcntl
LOCK_EX = fcntl.LOCK_EX
LOCK_SH = fcntl.LOCK_SH
LOCK_NB = fcntl.LOCK_NB
else: # pragma: no cover
raise RuntimeError('PortaLocker only defined for nt and posix platforms')
def nt_lock(file_, flags): # pragma: no cover
hfile = win32file._get_osfhandle(file_.fileno())
try:
win32file.LockFileEx(hfile, flags, 0, -0x10000, __overlapped)
except pywintypes.error as exc_value:
# error: (33, 'LockFileEx', 'The process cannot access the file
# because another process has locked a portion of the file.')
if exc_value[0] == 33:
raise LockException(LockException.LOCK_FAILED, exc_value[2])
else:
# Q: Are there exceptions/codes we should be dealing with
# here?
raise
def nt_unlock(file_): # pragma: no cover
hfile = win32file._get_osfhandle(file_.fileno())
try:
win32file.UnlockFileEx(hfile, 0, -0x10000, __overlapped)
except pywintypes.error as exc_value:
if exc_value[0] == 158:
# error: (158, 'UnlockFileEx', 'The segment is already '
# 'unlocked.')
# To match the 'posix' implementation, silently ignore this
# error
pass
else:
# Q: Are there exceptions/codes we should be dealing with
# here?
raise
def posix_lock(file_, flags):
try:
fcntl.flock(file_.fileno(), flags)
except IOError as exc_value:
# The exception code varies on different systems so we'll catch
# every IO error
raise LockException(exc_value)
def posix_unlock(file_):
fcntl.flock(file_.fileno(), fcntl.LOCK_UN)
if os.name == 'nt': # pragma: no cover
lock = nt_lock
unlock = nt_unlock
elif os.name == 'posix':
lock = posix_lock
unlock = posix_unlock
else: # pragma: no cover
raise RuntimeError('Your os %r is unsupported.' % os.name)
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