+
−"""
+
−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