# portalocker.py - Cross-platform (posix/nt) API for flock-style file locking.
#                  Requires python 1.5.2 or better.

"""Cross-platform (posix/nt) API for flock-style file locking.

Synopsis:

   import portalocker
   file = open("somefile", "r+")
   portalocker.lock(file, portalocker.LOCK_EX)
   file.seek(12)
   file.write("foo")
   file.close()

If you know what you're doing, you may choose to

   portalocker.unlock(file)

before closing the file, but why?

Methods:

   lock( file, flags )
   unlock( file )

Constants:

   LOCK_EX
   LOCK_SH
   LOCK_NB

I learned the win32 technique for locking files from sample code
provided by John Nielsen <nielsenjf@my-deja.com> in the documentation
that accompanies the win32 modules.

Author: Jonathan Feinberg <jdf@pobox.com>
Version: $Id: portalocker.py,v 1.3 2001/05/29 18:47:55 Administrator Exp $
"""

import os

if os.name == 'nt':
        import win32con
        import win32file
        import pywintypes
        LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
        LOCK_SH = 0 # the default
        LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
        # is there any reason not to reuse the following structure?
        __overlapped = pywintypes.OVERLAPPED()
elif os.name == 'posix':
        import fcntl
        LOCK_EX = fcntl.LOCK_EX
        LOCK_SH = fcntl.LOCK_SH
        LOCK_NB = fcntl.LOCK_NB
else:
        print 'warning, this device does not support file locking'
        LOCK_EX = None
        LOCK_SH = None
        LOCK_NB = None

if os.name == 'nt':
        def lock(file, flags):
                hfile = win32file._get_osfhandle(file.fileno())
                win32file.LockFileEx(hfile, flags, 0, 0x7fff0000, __overlapped)

        def unlock(file):
                hfile = win32file._get_osfhandle(file.fileno())
                win32file.UnlockFileEx(hfile, 0, 0x7fff0000, __overlapped)

elif os.name =='posix':
        def lock(file, flags):
                fcntl.flock(file.fileno(), flags)

        def unlock(file):
                fcntl.flock(file.fileno(), fcntl.LOCK_UN)

else:
        def lock(file, flags): pass
        def unlock(file): pass

if __name__ == '__main__':
        from time import time, strftime, localtime
        import sys

        log = open('log.txt', "a+")
        lock(log, LOCK_EX)

        timestamp = strftime("%m/%d/%Y %H:%M:%S\n", localtime(time()))
        log.write( timestamp )

        print "Wrote lines. Hit enter to release lock."
        dummy = sys.stdin.readline()

        log.close()