roundup/backends/portalocker.py

   1 # portalocker.py - Cross-platform (posix/nt) API for flock-style file locking.
   2 #                  Requires python 1.5.2 or better.
   3
   4 # ID line added by richard for Roundup file tracking
   5 # $Id: portalocker.py,v 1.9 2006-09-09 05:42:45 richard Exp $
   6
   7 """Cross-platform (posix/nt) API for flock-style file locking.
   8
   9 Synopsis::
  10
  11    import portalocker
  12    file = open("somefile", "r+")
  13    portalocker.lock(file, portalocker.LOCK_EX)
  14    file.seek(12)
  15    file.write("foo")
  16    file.close()
  17
  18 If you know what you're doing, you may choose to::
  19
  20    portalocker.unlock(file)
  21
  22 before closing the file, but why?
  23
  24 Methods::
  25
  26    lock( file, flags )
  27    unlock( file )
  28
  29 Constants::
  30
  31    LOCK_EX
  32    LOCK_SH
  33    LOCK_NB
  34
  35 I learned the win32 technique for locking files from sample code
  36 provided by John Nielsen <nielsenjf@my-deja.com> in the documentation
  37 that accompanies the win32 modules.
  38
  39 :Author: Jonathan Feinberg <jdf@pobox.com>
  40 :Version: Id: portalocker.py,v 1.3 2001/05/29 18:47:55 Administrator Exp
  41           **un-cvsified by richard so the version doesn't change**
  42 """
  43 __docformat__ = 'restructuredtext'
  44
  45 import os
  46
  47 if os.name == 'nt':
  48     import win32con
  49     import win32file
  50     import pywintypes
  51     LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
  52     LOCK_SH = 0 # the default
  53     LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
  54     # is there any reason not to reuse the following structure?
  55     __overlapped = pywintypes.OVERLAPPED()
  56 elif os.name == 'posix':
  57     import fcntl
  58     LOCK_EX = fcntl.LOCK_EX
  59     LOCK_SH = fcntl.LOCK_SH
  60     LOCK_NB = fcntl.LOCK_NB
  61 else:
  62     raise RuntimeError("PortaLocker only defined for nt and posix platforms")
  63
  64 if os.name == 'nt':
  65     # eugh, we want 0xffff0000 here, but python 2.3 won't let us :(
  66     FFFF0000 = -65536
  67     def lock(file, flags):
  68         hfile = win32file._get_osfhandle(file.fileno())
  69         # LockFileEx is not supported on all Win32 platforms (Win95, Win98,
  70         # WinME).
  71         # If it's not supported, win32file will raise an exception.
  72         # Try LockFileEx first, as it has more functionality and handles
  73         # blocking locks more efficiently.
  74         try:
  75             win32file.LockFileEx(hfile, flags, 0, FFFF0000, __overlapped)
  76         except win32file.error, e:
  77             import winerror
  78             # Propagate upwards all exceptions other than not-implemented.
  79             if e[0] != winerror.ERROR_CALL_NOT_IMPLEMENTED:
  80                 raise e
  81
  82             # LockFileEx is not supported. Use LockFile.
  83             # LockFile does not support shared locking -- always exclusive.
  84             # Care: the low/high length params are reversed compared to
  85             # LockFileEx.
  86             if not flags & LOCK_EX:
  87                 import warnings
  88                 warnings.warn("PortaLocker does not support shared "
  89                     "locking on Win9x", RuntimeWarning)
  90             # LockFile only supports immediate-fail locking.
  91             if flags & LOCK_NB:
  92                 win32file.LockFile(hfile, 0, 0, FFFF0000, 0)
  93             else:
  94                 # Emulate a blocking lock with a polling loop.
  95                 import time
  96                 while 1:
  97                     # Attempt a lock.
  98                     try:
  99                         win32file.LockFile(hfile, 0, 0, FFFF0000, 0)
 100                         break
 101                     except win32file.error, e:
 102                         # Propagate upwards all exceptions other than lock
 103                         # violation.
 104                         if e[0] != winerror.ERROR_LOCK_VIOLATION:
 105                             raise e
 106                     # Sleep and poll again.
 107                     time.sleep(0.1)
 108         # TODO: should this return the result of the lock?
 109
 110     def unlock(file):
 111         hfile = win32file._get_osfhandle(file.fileno())
 112         # UnlockFileEx is not supported on all Win32 platforms (Win95, Win98,
 113         # WinME).
 114         # If it's not supported, win32file will raise an api_error exception.
 115         try:
 116             win32file.UnlockFileEx(hfile, 0, FFFF0000, __overlapped)
 117         except win32file.error, e:
 118             import winerror
 119             # Propagate upwards all exceptions other than not-implemented.
 120             if e[0] != winerror.ERROR_CALL_NOT_IMPLEMENTED:
 121                 raise e
 122
 123             # UnlockFileEx is not supported. Use UnlockFile.
 124             # Care: the low/high length params are reversed compared to
 125             # UnLockFileEx.
 126             win32file.UnlockFile(hfile, 0, 0, FFFF0000, 0)
 127
 128 elif os.name =='posix':
 129     def lock(file, flags):
 130         fcntl.flock(file.fileno(), flags)
 131         # TODO: should this return the result of the lock?
 132
 133     def unlock(file):
 134         fcntl.flock(file.fileno(), fcntl.LOCK_UN)
 135
 136 if __name__ == '__main__':
 137     from time import time, strftime, localtime
 138     import sys
 139
 140     log = open('log.txt', "a+")
 141     lock(log, LOCK_EX)
 142
 143     timestamp = strftime("%m/%d/%Y %H:%M:%S\n", localtime(time()))
 144     log.write( timestamp )
 145
 146     print "Wrote lines. Hit enter to release lock."
 147     dummy = sys.stdin.readline()
 148
 149     log.close()
 150