server/pool.py
author sylvain.thenault@logilab.fr
Wed, 06 May 2009 17:24:48 +0200
branchtls-sprint
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parent 1132 96752791c2b6
child 1802 d628defebc17
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use yams.schema method for initial value
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"""CubicWeb server connections pool :
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* the rql repository has a limited number of connections pools, each of them
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  dealing with a set of connections on each source used by the repository
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* operation may be registered by hooks during a transaction, which will  be
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  fired when the pool is commited or rollbacked
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This module defined the `ConnectionsPool` class and a set of abstract classes
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for operation.
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:organization: Logilab
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:copyright: 2001-2009 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
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:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
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"""
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__docformat__ = "restructuredtext en"
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import sys
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class ConnectionsPool(object):
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    """handle connections on a set of sources, at some point associated to a
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    user session
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    """
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    def __init__(self, sources):
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        # dictionnary of (source, connection), indexed by sources'uri
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        self.source_cnxs = {}
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        for source in sources:
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            self.source_cnxs[source.uri] = (source, source.get_connection())
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        if not 'system' in self.source_cnxs:
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            self.source_cnxs['system'] = self.source_cnxs[sources[0].uri]
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        self._cursors = {}
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    def commit(self):
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        """commit the current transaction for this user"""
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        # FIXME: what happends if a commit fail
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        # would need a two phases commit or like, but I don't know how to do
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        # this using the db-api...
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        for source, cnx in self.source_cnxs.values():
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            # let exception propagates
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            cnx.commit()
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    def rollback(self):
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        """rollback the current transaction for this user"""
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        for source, cnx in self.source_cnxs.values():
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            # catch exceptions, rollback other sources anyway
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            try:
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                cnx.rollback()
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            except:
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                source.critical('rollback error', exc_info=sys.exc_info())
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    def close(self, i_know_what_i_do=False):
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        """close all connections in the pool"""
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        if i_know_what_i_do is not True: # unexpected closing safety belt
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            raise RuntimeError('pool shouldn\'t be closed')
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        for cu in self._cursors.values():
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            try:
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                cu.close()
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            except:
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                continue
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        for _, cnx in self.source_cnxs.values():
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            try:
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                cnx.close()
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            except:
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                continue
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    # internals ###############################################################
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    def pool_set(self, session):
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        """pool is being set"""
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        self.check_connections()
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    def pool_reset(self, session):
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        """pool is being reseted"""
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        for source, cnx in self.source_cnxs.values():
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            source.pool_reset(cnx)
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    def __getitem__(self, uri):
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        """subscription notation provide access to sources'cursors"""
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        try:
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            cursor = self._cursors[uri]
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        except KeyError:
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            cursor = self.source_cnxs[uri][1].cursor()
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            if cursor is not None:
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                # None possible on sources without cursor support such as ldap
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                self._cursors[uri] = cursor
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        return cursor
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    def sources(self):
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        """return the source objects handled by this pool"""
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        # implementation details of flying insert requires the system source
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        # first
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        yield self.source_cnxs['system']
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        for uri, (source, cursor) in self.source_cnxs.items():
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            if uri == 'system':
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                continue
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            yield source
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        #return [source_cnx[0] for source_cnx in self.source_cnxs.values()]
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    def source(self, uid):
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        """return the source object with the given uri"""
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        return self.source_cnxs[uid][0]
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    def connection(self, uid):
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        """return the connection on the source object with the given uri"""
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        return self.source_cnxs[uid][1]
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    def reconnect(self, source):
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        """reopen a connection for this source"""
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        source.info('trying to reconnect')
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        self.source_cnxs[source.uri] = (source, source.get_connection())        
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        del self._cursors[source.uri]
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    def check_connections(self):
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        for source, cnx in self.source_cnxs.itervalues():
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            newcnx = source.check_connection(cnx)
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            if newcnx is not None:
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                self.reset_connection(source, newcnx)
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    def reset_connection(self, source, cnx):
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        self.source_cnxs[source.uri] = (source, cnx)
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        self._cursors.pop(source.uri, None)
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class Operation(object):
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    """an operation is triggered on connections pool events related to
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    commit / rollback transations. Possible events are:
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    precommit:
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      the pool is preparing to commit. You shouldn't do anything things which
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      has to be reverted if the commit fail at this point, but you can freely
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      do any heavy computation or raise an exception if the commit can't go.
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      You can add some new operation during this phase but their precommit
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      event won't be triggered
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    commit:
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      the pool is preparing to commit. You should avoid to do to expensive
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      stuff or something that may cause an exception in this event
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    revertcommit:
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      if an operation failed while commited, this event is triggered for
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      all operations which had their commit event already to let them
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      revert things (including the operation which made fail the commit)
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    rollback:
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      the transaction has been either rollbacked either
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      * intentionaly
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      * a precommit event failed, all operations are rollbacked
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      * a commit event failed, all operations which are not been triggered for
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        commit are rollbacked
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    order of operations may be important, and is controlled according to:
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    * operation's class
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    """
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    def __init__(self, session, **kwargs):
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        self.session = session
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        self.user = session.user
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        self.repo = session.repo
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        self.schema = session.repo.schema
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        self.config = session.repo.config
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        self.__dict__.update(kwargs)
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        self.register(session)
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        # execution information
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        self.processed = None # 'precommit', 'commit'
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        self.failed = False
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    def register(self, session):
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        session.add_operation(self, self.insert_index())
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    def insert_index(self):
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        """return the index of  the lastest instance which is not a
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        LateOperation instance
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        """
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        for i, op in enumerate(self.session.pending_operations):
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            if isinstance(op, (LateOperation, SingleLastOperation)):
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                return i
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        return None
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    def handle_event(self, event):
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        """delegate event handling to the opertaion"""
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        getattr(self, event)()
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    def precommit_event(self):
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        """the observed connections pool is preparing a commit"""
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    def revertprecommit_event(self):
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        """an error went when pre-commiting this operation or a later one
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        should revert pre-commit's changes but take care, they may have not
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        been all considered if it's this operation which failed
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        """
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    def commit_event(self):
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        """the observed connections pool is commiting"""
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        raise NotImplementedError()
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    def revertcommit_event(self):
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        """an error went when commiting this operation or a later one
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        should revert commit's changes but take care, they may have not
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        been all considered if it's this operation which failed
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        """
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    def rollback_event(self):
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        """the observed connections pool has been rollbacked
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        do nothing by default, the operation will just be removed from the pool
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        operation list
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        """
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class PreCommitOperation(Operation):
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    """base class for operation only defining a precommit operation
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    """
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    def precommit_event(self):
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        """the observed connections pool is preparing a commit"""
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        raise NotImplementedError()
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    def commit_event(self):
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        """the observed connections pool is commiting"""
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class LateOperation(Operation):
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    """special operation which should be called after all possible (ie non late)
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    operations
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    """    
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    def insert_index(self):
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        """return the index of  the lastest instance which is not a
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        SingleLastOperation instance
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        """
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        for i, op in enumerate(self.session.pending_operations):
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            if isinstance(op, SingleLastOperation):
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                return i
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        return None
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class SingleOperation(Operation):
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    """special operation which should be called once"""    
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    def register(self, session):
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        """override register to handle cases where this operation has already
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        been added
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        """
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        operations = session.pending_operations
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        index = self.equivalent_index(operations)
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        if index is not None:
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            equivalent = operations.pop(index)
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        else:
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            equivalent = None
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        session.add_operation(self, self.insert_index())
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        return equivalent
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    def equivalent_index(self, operations):
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        """return the index of the equivalent operation if any"""
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        equivalents = [i for i, op in enumerate(operations)
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                       if op.__class__ is self.__class__]
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        if equivalents:
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            return equivalents[0]
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        return None
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class SingleLastOperation(SingleOperation):
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    """special operation which should be called once and after all other
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    operations
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    """    
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    def insert_index(self):
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        return None
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from logging import getLogger
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from cubicweb import set_log_methods
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set_log_methods(Operation, getLogger('cubicweb.session'))