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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. Transactions in bzr are not atomic - they
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depend on data ordering of writes, so we do not have commit or rollback
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facilities at the transaction level.
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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.
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Write transactions preserve dirty objects in the cache, though due to the
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write ordering approach we use for consistency 'dirty' is a misleading term.
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A dirty object is one we have modified.
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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 'precious' which indicates that
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repeated reads cannot be obtained if the object is ejected, or that
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the object is an expensive one for obtaining.
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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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"""Clean up this transaction."""
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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 is_clean(self, an_object):
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"""Return True if an_object is clean."""
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return an_object in self._clean_objects
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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.ReadOnlyObjectDirtiedError(an_object)
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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 WriteTransaction(ReadOnlyTransaction):
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"""A write transaction
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- caches domain objects
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- clean objects can be removed from the cache
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- dirty objects are retained.
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super(WriteTransaction, self).__init__()
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self._dirty_objects = set()
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def is_dirty(self, an_object):
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"""Return True if an_object is dirty."""
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return an_object in self._dirty_objects
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def register_dirty(self, an_object):
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"""Register an_object as being dirty.
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Dirty objects are not ejected from the identity map
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until the transaction finishes.
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self._dirty_objects.add(an_object)
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if self.is_clean(an_object):
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self._clean_objects.remove(an_object)
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del self._clean_queue[self._clean_queue.index(an_object)]
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class PassThroughTransaction(object):
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"""A pass through transaction
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- nothing ever gets into the identity map.
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"""Clean up this transaction."""
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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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def set_cache_size(self, ignored):
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"""Do nothing, we are passing through."""
added
removed
bzrlib/transactions.py
