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# Copyright (C) 2005, 2006 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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from bzrlib import errors
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from bzrlib.errors import LockError, LockContention
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from bzrlib.osutils import realpath
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from bzrlib.trace import mutter
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class _base_Lock(object):
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def _open(self, filename, filemode):
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self.f = open(filename, filemode)
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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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mutter("trying to create missing branch lock %r", filename)
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self.f = open(filename, 'wb+')
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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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############################################################
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class _fcntl_FileLock(_base_Lock):
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fcntl.lockf(self.f, fcntl.LOCK_UN)
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"""Clear the self.f attribute cleanly."""
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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, 'rb+')
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if e.errno in (errno.EACCES, errno.EPERM):
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raise errors.ReadOnlyLockError(e)
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self.filename = realpath(filename)
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if self.filename in self.open_locks:
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raise LockContention("Lock already held.")
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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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self.open_locks[self.filename] = 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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del self.open_locks[self.filename]
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class _fcntl_ReadLock(_fcntl_FileLock):
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def __init__(self, filename):
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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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WriteLock = _fcntl_WriteLock
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ReadLock = _fcntl_ReadLock
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import win32con, win32file, pywintypes
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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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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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overlapped = pywintypes.OVERLAPPED()
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win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped)
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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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class _w32c_WriteLock(_w32c_FileLock):
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def __init__(self, filename):
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_w32c_FileLock._lock(self, filename, 'rb+',
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WriteLock = _w32c_WriteLock
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ReadLock = _w32c_ReadLock
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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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class _msvc_FileLock(_base_Lock):
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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'),
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self.LOCK_SH | self.LOCK_NB)
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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, 'rb+'),
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self.LOCK_EX | self.LOCK_NB)
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def _msvc_lock(f, flags):
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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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fpos = os.lseek(fn, 0,0)
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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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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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lock_mode = msvcrt.LK_RLCK
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raise ValueError('Invalid lock mode: %r' % flags)
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msvcrt.locking(fn, lock_mode, -1)
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os.lseek(fn, fpos, 0)
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fpos = os.lseek(fn, 0,0)
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msvcrt.locking(fn, msvcrt.LK_UNLCK, -1)
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os.lseek(fn, fpos, 0)
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WriteLock = _msvc_WriteLock
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ReadLock = _msvc_ReadLock
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raise NotImplementedError("please write a locking method "
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"for platform %r" % sys.platform)
added
removed
bzrlib/lock.py
