"""
Portable file locking utilities.
Based partially on example by Jonathan Feignberg <jdf@pobox.com> in the Python
Cookbook, licensed under the Python Software License.
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/65203
Example Usage::
>>> from django.core.files import locks
>>> f = open('./file', 'wb')
>>> locks.lock(f, locks.LOCK_EX)
>>> f.write('Django')
>>> f.close()
"""
__all__ = ('LOCK_EX','LOCK_SH','LOCK_NB','lock','unlock')
system_type = None
try:
import win32con
import win32file
import pywintypes
LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
LOCK_SH = 0
LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
__overlapped = pywintypes.OVERLAPPED()
system_type = 'nt'
except (ImportError, AttributeError):
pass
try:
import fcntl
LOCK_EX = fcntl.LOCK_EX
LOCK_SH = fcntl.LOCK_SH
LOCK_NB = fcntl.LOCK_NB
system_type = 'posix'
except (ImportError, AttributeError):
pass
def fd(f):
"""Get a filedescriptor from something which could be a file or an fd."""
return hasattr(f, 'fileno') and f.fileno() or f
if system_type == 'nt':
def lock(file, flags):
hfile = win32file._get_osfhandle(fd(file))
win32file.LockFileEx(hfile, flags, 0, -0x10000, __overlapped)
def unlock(file):
hfile = win32file._get_osfhandle(fd(file))
win32file.UnlockFileEx(hfile, 0, -0x10000, __overlapped)
elif system_type == 'posix':
def lock(file, flags):
fcntl.lockf(fd(file), flags)
def unlock(file):
fcntl.lockf(fd(file), fcntl.LOCK_UN)
else:
# File locking is not supported.
LOCK_EX = LOCK_SH = LOCK_NB = None
# Dummy functions that don't do anything.
def lock(file, flags):
pass
def unlock(file):
pass
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