1 """

     2 Portable file locking utilities.

     3 

     4 Based partially on example by Jonathan Feignberg <jdf@pobox.com> in the Python

     5 Cookbook, licensed under the Python Software License.

     6 

     7     http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/65203

     8 

     9 Example Usage::

    10 

    11     >>> from django.core.files import locks

    12     >>> f = open('./file', 'wb')

    13     >>> locks.lock(f, locks.LOCK_EX)

    14     >>> f.write('Django')

    15     >>> f.close()

    16 """

    17 

    18 __all__ = ('LOCK_EX','LOCK_SH','LOCK_NB','lock','unlock')

    19 

    20 system_type = None

    21 

    22 try:

    23     import win32con

    24     import win32file

    25     import pywintypes

    26     LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK

    27     LOCK_SH = 0

    28     LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY

    29     __overlapped = pywintypes.OVERLAPPED()

    30     system_type = 'nt'

    31 except (ImportError, AttributeError):

    32     pass

    33 

    34 try:

    35     import fcntl

    36     LOCK_EX = fcntl.LOCK_EX

    37     LOCK_SH = fcntl.LOCK_SH

    38     LOCK_NB = fcntl.LOCK_NB

    39     system_type = 'posix'

    40 except (ImportError, AttributeError):

    41     pass

    42 

    43 def fd(f):

    44     """Get a filedescriptor from something which could be a file or an fd."""

    45     return hasattr(f, 'fileno') and f.fileno() or f

    46 

    47 if system_type == 'nt':

    48     def lock(file, flags):

    49         hfile = win32file._get_osfhandle(fd(file))

    50         win32file.LockFileEx(hfile, flags, 0, -0x10000, __overlapped)

    51 

    52     def unlock(file):

    53         hfile = win32file._get_osfhandle(fd(file))

    54         win32file.UnlockFileEx(hfile, 0, -0x10000, __overlapped)

    55 elif system_type == 'posix':

    56     def lock(file, flags):

    57         fcntl.lockf(fd(file), flags)

    58 

    59     def unlock(file):

    60         fcntl.lockf(fd(file), fcntl.LOCK_UN)

    61 else:

    62     # File locking is not supported.

    63     LOCK_EX = LOCK_SH = LOCK_NB = None

    64 

    65     # Dummy functions that don't do anything.

    66     def lock(file, flags):

    67         pass

    68 

    69     def unlock(file):

    70         pass