app/django/core/files/locks.py
author Daniel Hans <Daniel.M.Hans@gmail.com>
Tue, 03 Nov 2009 00:50:23 +0100
changeset 3075 1e78db95e38a
parent 323 ff1a9aa48cfd
permissions -rw-r--r--
getListContentForData function added to lists helper. It allows to manually set a list of entities which is to be displayed on the view. Previously, the only function was getListContent, but it retrived data on its own by a single query. The new function can be useful whenever it is impossible or very awkward to obtain entities in such a way (for example more sophisticated SQL statements). Additionally, the getListContent function is reconstructed so that it collects the data first and then calls getListContentForData.

"""
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