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# Copyright (C) 2005 by Canonical Ltd
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# Authors: Robert Collins <robert.collins@canonical.com>
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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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"""This module provides a transactional facility.
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Transactions provide hooks to allow data objects (i.e. inventory weaves or
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the revision-history file) to be placed in a registry and retrieved later
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during the same transaction. This allows for repeated read isolation. At
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the end of a transaction, a callback is issued to each registered changed
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item informing it whether it should commit or not. We provide a two layer
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facility - domain objects are notified first, then data objects.
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Read only transactions raise an assert when objects are listed as dirty
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against them - preventing unintended writes. Once all the data storage is
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hooked into this facility, it might be nice to have a readonly transaction
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that just excepts on commit, for testing or simulating of things.
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Write transactions queue all changes in the transaction (which may in the
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future involve writing them to uncommitted atomic files in preparation
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for commit - i.e. on network connections where latency matters) and then
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notify each object of commit or rollback.
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Both read and write transactions *may* flush unchanged objects out of
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memory, unless they are marked as 'preserve' which indicates that
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repeated reads cannot be obtained if the object is ejected.
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import bzrlib.errors as errors
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from bzrlib.identitymap import IdentityMap, NullIdentityMap
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from bzrlib.trace import mutter
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class ReadOnlyTransaction(object):
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"""A read only unit of work for data objects."""
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"""ReadOnlyTransactions cannot commit."""
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raise errors.CommitNotPossible('In a read only transaction')
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"""Clean up this transaction
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This will rollback on transactions that can if they have nto been
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super(ReadOnlyTransaction, self).__init__()
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self.map = IdentityMap()
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self._clean_objects = set()
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self._clean_queue = []
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self._precious_objects = set()
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def register_clean(self, an_object, precious=False):
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"""Register an_object as being clean.
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If the precious hint is True, the object will not
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be ejected from the object identity map ever.
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self._clean_objects.add(an_object)
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self._clean_queue.append(an_object)
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self._precious_objects.add(an_object)
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def register_dirty(self, an_object):
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"""Register an_object as being dirty."""
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raise errors.ReadOnlyError(
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"Cannot dirty objects in a read only transaction")
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"""Let people call this even though nothing has to happen."""
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def set_cache_size(self, size):
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"""Set a new cache size."""
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"""Trim the cache back if needed."""
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if self._limit < 0 or self._limit - len(self._clean_objects) > 0:
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needed = len(self._clean_objects) - self._limit
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while needed and offset < len(self._clean_objects):
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# references we know of:
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# temp passed to getrefcount in our frame
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# temp in getrefcount's frame
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if (sys.getrefcount(self._clean_queue[offset]) <= 7 and
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not self._clean_queue[offset] in self._precious_objects):
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removed = self._clean_queue[offset]
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self._clean_objects.remove(removed)
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del self._clean_queue[offset]
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self.map.remove_object(removed)
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mutter('removed object %r', removed)
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class PassThroughTransaction(object):
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"""A pass through transaction
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- all actions are committed immediately.
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- rollback is not supported.
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- commit() is a no-op.
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"""PassThroughTransactions have nothing to do."""
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"""Clean up this transaction
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This will rollback on transactions that can if they have nto been
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super(PassThroughTransaction, self).__init__()
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self.map = NullIdentityMap()
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def register_clean(self, an_object, precious=False):
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"""Register an_object as being clean.
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Note that precious is only a hint, and PassThroughTransaction
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def register_dirty(self, an_object):
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"""Register an_object as being dirty."""
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"""Cannot rollback a pass through transaction."""
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raise errors.AlreadyCommitted
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def set_cache_size(self, ignored):
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"""Do nothing, we are passing through."""
added
removed
bzrlib/transactions.py
