"""

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