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# Copyright (C) 2005, 2006, 2007 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 using OS file locks or file existence.
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Note: This method of locking is generally deprecated in favour of LockDir, but
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is used to lock local WorkingTrees, and by some old formats. It's accessed
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through Transport.lock_read(), etc.
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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. That reentrancy is provided by
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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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have_ctypes_win32 = False
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if sys.platform == 'win32':
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import win32con, win32file, pywintypes, winerror
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have_ctypes_win32 = True
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class _OSLock(object):
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def _open(self, filename, filemode):
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self.filename = osutils.realpath(filename)
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self.f = open(self.filename, filemode)
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if e.errno in (errno.EACCES, errno.EPERM):
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raise errors.LockFailed(self.filename, str(e))
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if e.errno != errno.ENOENT:
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# maybe this is an old branch (before may 2005)
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trace.mutter("trying to create missing lock %r", self.filename)
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self.f = open(self.filename, 'wb+')
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"""Clear the self.f attribute cleanly."""
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from warnings import warn
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warn("lock on %r not released" % self.f)
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raise NotImplementedError()
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LOCK_SH = fcntl.LOCK_SH
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LOCK_NB = fcntl.LOCK_NB
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lock_EX = fcntl.LOCK_EX
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class _fcntl_FileLock(_OSLock):
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fcntl.lockf(self.f, fcntl.LOCK_UN)
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class _fcntl_WriteLock(_fcntl_FileLock):
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def __init__(self, filename):
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super(_fcntl_WriteLock, self).__init__()
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# Check we can grab a lock before we actually open the file.
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self.filename = osutils.realpath(filename)
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if self.filename in _fcntl_WriteLock._open_locks:
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raise errors.LockContention(self.filename)
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self._open(self.filename, 'rb+')
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# reserve a slot for this lock - even if the lockf call fails,
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# at thisi point unlock() will be called, because self.f is set.
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# TODO: make this fully threadsafe, if we decide we care.
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_fcntl_WriteLock._open_locks.add(self.filename)
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# LOCK_NB will cause IOError to be raised if we can't grab a
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fcntl.lockf(self.f, fcntl.LOCK_EX | fcntl.LOCK_NB)
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if e.errno in (errno.EAGAIN, errno.EACCES):
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# We couldn't grab the lock
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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 errors.LockContention(e)
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_fcntl_WriteLock._open_locks.remove(self.filename)
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class _fcntl_ReadLock(_fcntl_FileLock):
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def __init__(self, filename):
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super(_fcntl_ReadLock, self).__init__()
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self.filename = osutils.realpath(filename)
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_fcntl_ReadLock._open_locks.setdefault(self.filename, 0)
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_fcntl_ReadLock._open_locks[self.filename] += 1
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self._open(filename, 'rb')
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# LOCK_NB will cause IOError to be raised if we can't grab a
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fcntl.lockf(self.f, fcntl.LOCK_SH | fcntl.LOCK_NB)
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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 errors.LockContention(e)
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count = _fcntl_ReadLock._open_locks[self.filename]
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del _fcntl_ReadLock._open_locks[self.filename]
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_fcntl_ReadLock._open_locks[self.filename] = count - 1
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def temporary_write_lock(self):
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"""Try to grab a write lock on the file.
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On platforms that support it, this will upgrade to a write lock
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without unlocking the file.
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Otherwise, this will release the read lock, and try to acquire a
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:return: A token which can be used to switch back to a read lock.
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if self.filename in _fcntl_WriteLock._open_locks:
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raise AssertionError('file already locked: %r'
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wlock = _fcntl_TemporaryWriteLock(self)
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except errors.LockError:
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# We didn't unlock, so we can just return 'self'
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class _fcntl_TemporaryWriteLock(_OSLock):
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"""A token used when grabbing a temporary_write_lock.
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Call restore_read_lock() when you are done with the write lock.
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def __init__(self, read_lock):
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super(_fcntl_TemporaryWriteLock, self).__init__()
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self._read_lock = read_lock
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self.filename = read_lock.filename
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count = _fcntl_ReadLock._open_locks[self.filename]
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# Something else also has a read-lock, so we cannot grab a
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raise errors.LockContention(self.filename)
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if self.filename in _fcntl_WriteLock._open_locks:
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raise AssertionError('file already locked: %r'
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# See if we can open the file for writing. Another process might
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# have a read lock. We don't use self._open() because we don't want
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# to create the file if it exists. That would have already been
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# done by _fcntl_ReadLock
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new_f = open(self.filename, 'rb+')
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if e.errno in (errno.EACCES, errno.EPERM):
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raise errors.LockFailed(self.filename, str(e))
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# LOCK_NB will cause IOError to be raised if we can't grab a
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fcntl.lockf(new_f, fcntl.LOCK_EX | fcntl.LOCK_NB)
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# TODO: Raise a more specific error based on the type of error
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raise errors.LockContention(e)
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_fcntl_WriteLock._open_locks.add(self.filename)
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def restore_read_lock(self):
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"""Restore the original ReadLock."""
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# For fcntl, since we never released the read lock, just release the
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# write lock, and return the original lock.
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fcntl.lockf(self.f, fcntl.LOCK_UN)
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_fcntl_WriteLock._open_locks.remove(self.filename)
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# Avoid reference cycles
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read_lock = self._read_lock
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self._read_lock = None
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_lock_classes.append(('fcntl', _fcntl_WriteLock, _fcntl_ReadLock))
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if have_pywin32 and sys.platform == 'win32':
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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(_OSLock):
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def _lock(self, filename, openmode, lockmode):
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self._open(filename, openmode)
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self.hfile = msvcrt.get_osfhandle(self.f.fileno())
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overlapped = pywintypes.OVERLAPPED()
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win32file.LockFileEx(self.hfile, lockmode, 0, 0x7fff0000,
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except pywintypes.error, e:
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if e.args[0] in (winerror.ERROR_LOCK_VIOLATION,):
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raise errors.LockContention(filename)
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## import pdb; pdb.set_trace()
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raise errors.LockContention(e)
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overlapped = pywintypes.OVERLAPPED()
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win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped)
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raise errors.LockContention(e)
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class _w32c_ReadLock(_w32c_FileLock):
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def __init__(self, filename):
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super(_w32c_ReadLock, self).__init__()
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self._lock(filename, 'rb', LOCK_SH + LOCK_NB)
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def temporary_write_lock(self):
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"""Try to grab a write lock on the file.
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On platforms that support it, this will upgrade to a write lock
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without unlocking the file.
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Otherwise, this will release the read lock, and try to acquire a
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:return: A token which can be used to switch back to a read lock.
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# I can't find a way to upgrade a read lock to a write lock without
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# unlocking first. So here, we do just that.
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wlock = _w32c_WriteLock(self.filename)
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except errors.LockError:
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return False, _w32c_ReadLock(self.filename)
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class _w32c_WriteLock(_w32c_FileLock):
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def __init__(self, filename):
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super(_w32c_WriteLock, self).__init__()
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self._lock(filename, 'rb+', LOCK_EX + LOCK_NB)
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def restore_read_lock(self):
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"""Restore the original ReadLock."""
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# For win32 we had to completely let go of the original lock, so we
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# just unlock and create a new read lock.
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return _w32c_ReadLock(self.filename)
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_lock_classes.append(('pywin32', _w32c_WriteLock, _w32c_ReadLock))
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if have_ctypes_win32:
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# These constants were copied from the win32con.py module.
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LOCKFILE_FAIL_IMMEDIATELY = 1
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LOCKFILE_EXCLUSIVE_LOCK = 2
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# Constant taken from winerror.py module
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ERROR_LOCK_VIOLATION = 33
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LOCK_EX = LOCKFILE_EXCLUSIVE_LOCK
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LOCK_NB = LOCKFILE_FAIL_IMMEDIATELY
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_LockFileEx = ctypes.windll.kernel32.LockFileEx
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_UnlockFileEx = ctypes.windll.kernel32.UnlockFileEx
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_GetLastError = ctypes.windll.kernel32.GetLastError
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### Define the OVERLAPPED structure.
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# http://msdn2.microsoft.com/en-us/library/ms684342.aspx
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# typedef struct _OVERLAPPED {
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# ULONG_PTR Internal;
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# ULONG_PTR InternalHigh;
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class _inner_struct(ctypes.Structure):
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_fields_ = [('Offset', ctypes.c_uint), # DWORD
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('OffsetHigh', ctypes.c_uint), # DWORD
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class _inner_union(ctypes.Union):
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_fields_ = [('anon_struct', _inner_struct), # struct
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('Pointer', ctypes.c_void_p), # PVOID
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class OVERLAPPED(ctypes.Structure):
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_fields_ = [('Internal', ctypes.c_void_p), # ULONG_PTR
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('InternalHigh', ctypes.c_void_p), # ULONG_PTR
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('_inner_union', _inner_union),
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('hEvent', ctypes.c_void_p), # HANDLE
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class _ctypes_FileLock(_OSLock):
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def _lock(self, filename, openmode, lockmode):
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self._open(filename, openmode)
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self.hfile = msvcrt.get_osfhandle(self.f.fileno())
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overlapped = OVERLAPPED()
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result = _LockFileEx(self.hfile, # HANDLE hFile
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lockmode, # DWORD dwFlags
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0, # DWORD dwReserved
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0x7fffffff, # DWORD nNumberOfBytesToLockLow
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0x00000000, # DWORD nNumberOfBytesToLockHigh
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ctypes.byref(overlapped), # lpOverlapped
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last_err = _GetLastError()
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if last_err in (ERROR_LOCK_VIOLATION,):
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raise errors.LockContention(filename)
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raise errors.LockContention('Unknown locking error: %s'
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overlapped = OVERLAPPED()
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result = _UnlockFileEx(self.hfile, # HANDLE hFile
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0, # DWORD dwReserved
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0x7fffffff, # DWORD nNumberOfBytesToLockLow
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0x00000000, # DWORD nNumberOfBytesToLockHigh
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ctypes.byref(overlapped), # lpOverlapped
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last_err = _GetLastError()
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raise errors.LockContention('Unknown unlocking error: %s'
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class _ctypes_ReadLock(_ctypes_FileLock):
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def __init__(self, filename):
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super(_ctypes_ReadLock, self).__init__()
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self._lock(filename, 'rb', LOCK_SH + LOCK_NB)
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def temporary_write_lock(self):
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"""Try to grab a write lock on the file.
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On platforms that support it, this will upgrade to a write lock
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without unlocking the file.
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Otherwise, this will release the read lock, and try to acquire a
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:return: A token which can be used to switch back to a read lock.
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# I can't find a way to upgrade a read lock to a write lock without
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# unlocking first. So here, we do just that.
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wlock = _ctypes_WriteLock(self.filename)
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except errors.LockError:
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return False, _ctypes_ReadLock(self.filename)
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class _ctypes_WriteLock(_ctypes_FileLock):
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def __init__(self, filename):
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super(_ctypes_WriteLock, self).__init__()
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self._lock(filename, 'rb+', LOCK_EX + LOCK_NB)
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def restore_read_lock(self):
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"""Restore the original ReadLock."""
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# For win32 we had to completely let go of the original lock, so we
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# just unlock and create a new read lock.
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return _ctypes_ReadLock(self.filename)
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_lock_classes.append(('ctypes', _ctypes_WriteLock, _ctypes_ReadLock))
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if len(_lock_classes) == 0:
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raise NotImplementedError(
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"We must have one of fcntl, pywin32, or ctypes available"
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" to support OS locking."
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# We default to using the first available lock class.
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_lock_type, WriteLock, ReadLock = _lock_classes[0]
added
removed
bzrlib/lock.py
