~bzr-pqm/bzr/bzr.dev

577 by Martin Pool
- merge portable lock module from John
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# Copyright (C) 2005 Canonical Ltd
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
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"""Locking wrappers.
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This only does local locking using OS locks for now.
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This module causes two methods, lock() and unlock() to be defined in
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any way that works on the current platform.
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It is not specified whether these locks are reentrant (i.e. can be
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taken repeatedly by a single process) or whether they exclude
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different threads in a single process.  
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Eventually we may need to use some kind of lock representation that
614 by Martin Pool
- unify two defintions of LockError
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will work on a dumb filesystem without actual locking primitives.
615 by Martin Pool
Major rework of locking code:
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This defines two classes: ReadLock and WriteLock, which can be
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implemented in different ways on different platforms.  Both have an
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unlock() method.
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- unify two defintions of LockError
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"""
577 by Martin Pool
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1185.65.29 by Robert Collins
Implement final review suggestions.
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import errno
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import os
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- create branch lock files if they don't exist
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import sys
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656 by Martin Pool
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from bzrlib.trace import mutter, note, warning
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from bzrlib.errors import LockError
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615 by Martin Pool
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class _base_Lock(object):
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    def _open(self, filename, filemode):
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        try:
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            self.f = open(filename, filemode)
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            return self.f
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        except IOError, e:
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            if e.errno != errno.ENOENT:
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                raise
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            # maybe this is an old branch (before may 2005)
1185.31.4 by John Arbash Meinel
Fixing mutter() calls to not have to do string processing.
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            mutter("trying to create missing branch lock %r", filename)
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            self.f = open(filename, 'wb+')
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            return self.f
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615 by Martin Pool
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    def __del__(self):
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        if self.f:
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            from warnings import warn
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            warn("lock on %r not released" % self.f)
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            self.unlock()
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    def unlock(self):
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        raise NotImplementedError()
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############################################################
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# msvcrt locks
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try:
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    import fcntl
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    class _fcntl_FileLock(_base_Lock):
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        f = None
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        def unlock(self):
1185.9.2 by Harald Meland
Use fcntl.lockf() rather than fcntl.flock() to support NFS file systems.
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            fcntl.lockf(self.f, fcntl.LOCK_UN)
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            self.f.close()
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            del self.f 
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    class _fcntl_WriteLock(_fcntl_FileLock):
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        def __init__(self, filename):
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            # standard IO errors get exposed directly.
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            self._open(filename, 'wb')
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            try:
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                fcntl.lockf(self.f, fcntl.LOCK_EX)
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            except IOError, e:
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                # we should be more precise about whats a locking
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                # error and whats a random-other error
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                raise LockError(e)
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    class _fcntl_ReadLock(_fcntl_FileLock):
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        def __init__(self, filename):
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            # standard IO errors get exposed directly.
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            self._open(filename, 'rb')
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            try:
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                fcntl.lockf(self.f, fcntl.LOCK_SH)
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            except IOError, e:
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                # we should be more precise about whats a locking
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                # error and whats a random-other error
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                raise LockError(e)
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    WriteLock = _fcntl_WriteLock
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    ReadLock = _fcntl_ReadLock
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1185.65.29 by Robert Collins
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577 by Martin Pool
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except ImportError:
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    try:
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        import win32con, win32file, pywintypes
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1185.23.3 by Aaron Bentley
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        LOCK_SH = 0 # the default
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        LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
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        LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
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        class _w32c_FileLock(_base_Lock):
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            def _lock(self, filename, openmode, lockmode):
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                try:
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                    self._open(filename, openmode)
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                    self.hfile = win32file._get_osfhandle(self.f.fileno())
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                    overlapped = pywintypes.OVERLAPPED()
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                    win32file.LockFileEx(self.hfile, lockmode, 0, 0x7fff0000, overlapped)
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                except Exception, e:
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                    raise LockError(e)
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            def unlock(self):
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                try:
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                    overlapped = pywintypes.OVERLAPPED()
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                    win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped)
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                    self.f.close()
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                    self.f = None
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                except Exception, e:
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                    raise LockError(e)
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        class _w32c_ReadLock(_w32c_FileLock):
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            def __init__(self, filename):
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                _w32c_FileLock._lock(self, filename, 'rb',
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                                     LOCK_NB)
615 by Martin Pool
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        class _w32c_WriteLock(_w32c_FileLock):
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            def __init__(self, filename):
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                _w32c_FileLock._lock(self, filename, 'wb',
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win32 locking fix from Belchenko
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                                     LOCK_EX + LOCK_NB)
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        WriteLock = _w32c_WriteLock
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        ReadLock = _w32c_ReadLock
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    except ImportError:
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        try:
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            import msvcrt
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            # Unfortunately, msvcrt.locking() doesn't distinguish between
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            # read locks and write locks. Also, the way the combinations
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            # work to get non-blocking is not the same, so we
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            # have to write extra special functions here.
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615 by Martin Pool
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            class _msvc_FileLock(_base_Lock):
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                LOCK_SH = 1
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                LOCK_EX = 2
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                LOCK_NB = 4
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                def unlock(self):
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                    _msvc_unlock(self.f)
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                    self.f.close()
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                    self.f = None
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            class _msvc_ReadLock(_msvc_FileLock):
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                def __init__(self, filename):
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                    _msvc_lock(self._open(filename, 'rb'), self.LOCK_SH)
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            class _msvc_WriteLock(_msvc_FileLock):
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                def __init__(self, filename):
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                    _msvc_lock(self._open(filename, 'wb'), self.LOCK_EX)
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            def _msvc_lock(f, flags):
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                try:
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                    # Unfortunately, msvcrt.LK_RLCK is equivalent to msvcrt.LK_LOCK
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                    # according to the comments, LK_RLCK is open the lock for writing.
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                    # Unfortunately, msvcrt.locking() also has the side effect that it
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                    # will only block for 10 seconds at most, and then it will throw an
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                    # exception, this isn't terrible, though.
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                    if type(f) == file:
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                        fpos = f.tell()
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                        fn = f.fileno()
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                        f.seek(0)
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                    else:
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                        fn = f
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                        fpos = os.lseek(fn, 0,0)
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                        os.lseek(fn, 0,0)
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951 by Martin Pool
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                    if flags & _msvc_FileLock.LOCK_SH:
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                        if flags & _msvc_FileLock.LOCK_NB:
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                            lock_mode = msvcrt.LK_NBLCK
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                        else:
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                            lock_mode = msvcrt.LK_LOCK
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                    elif flags & _msvc_FileLock.LOCK_EX:
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                        if flags & _msvc_FileLock.LOCK_NB:
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                            lock_mode = msvcrt.LK_NBRLCK
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                        else:
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                            lock_mode = msvcrt.LK_RLCK
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                    else:
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                        raise ValueError('Invalid lock mode: %r' % flags)
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                    try:
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                        msvcrt.locking(fn, lock_mode, -1)
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                    finally:
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                        os.lseek(fn, fpos, 0)
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                except Exception, e:
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                    raise LockError(e)
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615 by Martin Pool
Major rework of locking code:
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            def _msvc_unlock(f):
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                try:
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                    if type(f) == file:
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                        fpos = f.tell()
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                        fn = f.fileno()
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                        f.seek(0)
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                    else:
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                        fn = f
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                        fpos = os.lseek(fn, 0,0)
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                        os.lseek(fn, 0,0)
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                    try:
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                        msvcrt.locking(fn, msvcrt.LK_UNLCK, -1)
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                    finally:
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                        os.lseek(fn, fpos, 0)
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                except Exception, e:
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                    raise LockError(e)
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Major rework of locking code:
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            WriteLock = _msvc_WriteLock
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            ReadLock = _msvc_ReadLock
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        except ImportError:
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            raise NotImplementedError("please write a locking method "
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                                      "for platform %r" % sys.platform)
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- merge portable lock module from John
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