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# Copyright (C) 2005-2010 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 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 __future__ import absolute_import
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from .hooks import Hooks
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from .i18n import gettext
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class LockHooks(Hooks):
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Hooks.__init__(self, "breezy.lock", "Lock.hooks")
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"Called with a breezy.lock.LockResult when a physical lock is "
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"Called with a breezy.lock.LockResult when a physical lock is "
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"Called with a breezy.lock.LockResult when a physical lock is "
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"""Base class for locks.
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:cvar hooks: Hook dictionary for operations on locks.
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class LockResult(object):
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"""Result of an operation on a lock; passed to a hook"""
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def __init__(self, lock_url, details=None):
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"""Create a lock result for lock with optional details about the lock."""
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self.lock_url = lock_url
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self.details = details
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def __eq__(self, other):
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return self.lock_url == other.lock_url and self.details == other.details
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return '%s(%s, %s)' % (self.__class__.__name__,
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self.lock_url, self.details)
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class LogicalLockResult(object):
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"""The result of a lock_read/lock_write/lock_tree_write call on lockables.
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:ivar unlock: A callable which will unlock the lock.
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def __init__(self, unlock, token=None):
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return "LogicalLockResult(%s)" % (self.unlock)
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def __exit__(self, exc_type, exc_val, exc_tb):
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# If there was an error raised, prefer the original one
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except BaseException:
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def cant_unlock_not_held(locked_object):
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"""An attempt to unlock failed because the object was not locked.
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This provides a policy point from which we can generate either a warning or
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# This is typically masking some other error and called from a finally
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# block, so it's useful to have the option not to generate a new error
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# here. You can use -Werror to make it fatal. It should possibly also
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if 'unlock' in debug.debug_flags:
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warnings.warn("%r is already unlocked" % (locked_object,),
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raise errors.LockNotHeld(locked_object)
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have_ctypes_win32 = False
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if sys.platform == 'win32':
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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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raise NotImplementedError()
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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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if self.filename in _fcntl_ReadLock._open_locks:
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if 'strict_locks' in debug.debug_flags:
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raise errors.LockContention(self.filename)
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trace.mutter('Write lock taken w/ an open read lock on: %s'
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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 this 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(self.filename, 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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if self.filename in _fcntl_WriteLock._open_locks:
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if 'strict_locks' in debug.debug_flags:
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# We raise before calling _open so we don't need to
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raise errors.LockContention(self.filename)
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trace.mutter('Read lock taken w/ an open write lock on: %s'
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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(self.filename, 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(self.filename, 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
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# the 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_ctypes_win32:
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from ctypes.wintypes import DWORD, LPWSTR
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LPSECURITY_ATTRIBUTES = ctypes.c_void_p # used as NULL no need to declare
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HANDLE = ctypes.c_int # rather than unsigned as in ctypes.wintypes
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_function_name = "CreateFileW"
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# CreateFile <http://msdn.microsoft.com/en-us/library/aa363858.aspx>
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_CreateFile = ctypes.WINFUNCTYPE(
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HANDLE, # return value
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DWORD, # dwDesiredAccess
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LPSECURITY_ATTRIBUTES, # lpSecurityAttributes
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DWORD, # dwCreationDisposition
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DWORD, # dwFlagsAndAttributes
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HANDLE # hTemplateFile
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)((_function_name, ctypes.windll.kernel32))
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INVALID_HANDLE_VALUE = -1
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GENERIC_READ = 0x80000000
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GENERIC_WRITE = 0x40000000
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FILE_ATTRIBUTE_NORMAL = 128
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ERROR_ACCESS_DENIED = 5
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ERROR_SHARING_VIOLATION = 32
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class _ctypes_FileLock(_OSLock):
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def _open(self, filename, access, share, cflags, pymode):
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self.filename = osutils.realpath(filename)
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handle = _CreateFile(filename, access, share, None, OPEN_ALWAYS,
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FILE_ATTRIBUTE_NORMAL, 0)
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if handle in (INVALID_HANDLE_VALUE, 0):
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e = ctypes.WinError()
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if e.args[0] == ERROR_ACCESS_DENIED:
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raise errors.LockFailed(filename, e)
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if e.args[0] == ERROR_SHARING_VIOLATION:
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raise errors.LockContention(filename, e)
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fd = msvcrt.open_osfhandle(handle, cflags)
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self.f = os.fdopen(fd, pymode)
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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._open(filename, GENERIC_READ, FILE_SHARE_READ, os.O_RDONLY,
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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._open(filename, GENERIC_READ | GENERIC_WRITE, 0, os.O_RDWR,
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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 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]
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class _RelockDebugMixin(object):
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"""Mixin support for -Drelock flag.
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Add this as a base class then call self._note_lock with 'r' or 'w' when
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acquiring a read- or write-lock. If this object was previously locked (and
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locked the same way), and -Drelock is set, then this will trace.note a
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def _note_lock(self, lock_type):
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if 'relock' in debug.debug_flags and self._prev_lock == lock_type:
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trace.note(gettext('{0!r} was {1} locked again'), self, type_name)
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self._prev_lock = lock_type
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@contextlib.contextmanager
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def write_locked(lockable):
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lockable.lock_write()
added
removed
breezy/lock.py
