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# Copyright 2011 Canonical Ltd.
#
# This file is part of u1db.
#
# u1db is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License version 3
# as published by the Free Software Foundation.
#
# u1db is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with u1db. If not, see <http://www.gnu.org/licenses/>.
"""VectorClockRev helper class."""
class VectorClockRev(object):
"""Track vector clocks for multiple replica ids.
This allows simple comparison to determine if one VectorClockRev is
newer/older/in-conflict-with another VectorClockRev without having to
examine history. Every replica has a strictly increasing revision. When
creating a new revision, they include all revisions for all other replicas
which the new revision dominates, and increment their own revision to
something greater than the current value.
"""
def __init__(self, value):
self._values = self._expand(value)
def __repr__(self):
s = self.as_str()
return '%s(%s)' % (self.__class__.__name__, s)
def as_str(self):
s = '|'.join(['%s:%d' % (m, r) for m, r
in sorted(self._values.items())])
return s
def _expand(self, value):
result = {}
if value is None:
return result
for replica_info in value.split('|'):
replica_uid, counter = replica_info.split(':')
counter = int(counter)
result[replica_uid] = counter
return result
def is_newer(self, other):
"""Is this VectorClockRev strictly newer than other.
"""
if not self._values:
return False
if not other._values:
return True
this_is_newer = False
other_expand = dict(other._values)
for key, value in self._values.iteritems():
if key in other_expand:
other_value = other_expand.pop(key)
if other_value > value:
return False
elif other_value < value:
this_is_newer = True
else:
this_is_newer = True
if other_expand:
return False
return this_is_newer
def increment(self, replica_uid):
"""Increase the 'replica_uid' section of this vector clock.
:return: A string representing the new vector clock value
"""
self._values[replica_uid] = self._values.get(replica_uid, 0) + 1
def maximize(self, other_vcr):
for replica_uid, counter in other_vcr._values.iteritems():
if replica_uid not in self._values:
self._values[replica_uid] = counter
else:
this_counter = self._values[replica_uid]
if this_counter < counter:
self._values[replica_uid] = counter
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