fcntl win32/posix

# 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  in the documentation
that accompanies the win32 modules.

Author: Jonathan Feinberg 
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:
 raise RuntimeError("PortaLocker only defined for nt and posix platforms")

if os.name == 'nt':
 def lock(file, flags):
  hfile = win32file._get_osfhandle(file.fileno())
  win32file.LockFileEx(hfile, flags, 0, 0xffff0000, __overlapped)

 def unlock(file):
  hfile = win32file._get_osfhandle(file.fileno())
  win32file.UnlockFileEx(hfile, 0, 0xffff0000, __overlapped)

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

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

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

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