Synnefo

                     Commission, Provision, ProvisionLog, now,

                     db_get_entity, db_get_holding, db_get_policy,

                     db_get_commission, db_filter_provision)

                e = db_get_entity(entity=entity, key=key, for_update=True)

                    policy = db_get_policy(policy=policy, for_update=True)

            h = db_get_holding(entity=entity, resource=resource,

                               for_update=True)

                h = db_get_holding(entity=entity, resource=resource,

                                   for_update=True)

            h = db_get_holding(entity=entity, resource=resource,

                               for_update=True)

                h = db_get_holding(entity=entity, resource=resource,

                                   for_update=True)

            h = db_get_holding(entity=entity, resource=resource,

                               for_update=True)

                h = db_get_holding(entity=entity, resource=resource,

                                   for_update=True)

                    h = db_get_holding(entity=entity, resource=resource,

                                       for_update=True)

                h = db_get_holding(entity=entity, resource=resource,

                                   for_update=True)

                th = db_get_holding(entity=target, resource=resource,

                                    for_update=True)

                c = db_get_commission(clientkey=clientkey, serial=serial,

                                      for_update=True)

            provisions = db_filter_provision(serial=serial, for_update=True)

                    h = db_get_holding(entity=pv.entity.entity,

                                       resource=pv.resource, for_update=True)

                    th = db_get_holding(entity=t, resource=pv.resource,

                                        for_update=True)

                c = db_get_commission(clientkey=clientkey, serial=serial,

                                      for_update=True)

            provisions = db_filter_provision(serial=serial, for_update=True)

                    h = db_get_holding(entity=pv.entity.entity,

                                       resource=pv.resource, for_update=True)

                    th = db_get_holding(entity=t, resource=pv.resource,

                                        for_update=True)

                e = db_get_entity(entity=entity, key=key, for_update=True)

# Copyright 2012 GRNET S.A. All rights reserved.

#

# Redistribution and use in source and binary forms, with or without

# modification, are permitted provided that the following conditions

# are met:

#

#   1. Redistributions of source code must retain the above copyright

#      notice, this list of conditions and the following disclaimer.

#

#  2. Redistributions in binary form must reproduce the above copyright

#     notice, this list of conditions and the following disclaimer in the

#     documentation and/or other materials provided with the distribution.

#

# THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

# ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

# SUCH DAMAGE.

#

# The views and conclusions contained in the software and documentation are

# those of the authors and should not be interpreted as representing official

# policies, either expressed or implied, of GRNET S.A.

from django.db import connections

from django.db.models import Manager

from django.db.models.query import QuerySet

class ForUpdateManager(Manager):

    """ Model manager implementing SELECT .. FOR UPDATE statement

        This manager implements select_for_update() method in order to use

        row-level locking in the database and guarantee exclusive access, since

        this method is only implemented in Django>=1.4.

        Non-blocking reads are not implemented, and each query including a row

        that is locked by another transaction will block until the lock is

        released. Also care must be taken in order to avoid deadlocks or retry

        transactions that abort due to deadlocks.

        Example:

            networks = Network.objects.select_for_update().filter(public=True)

    """

    def __init__(self, *args, **kwargs):

        super(ForUpdateManager, self).__init__(*args, **kwargs)

        self._select_for_update = False

    def filter(self, *args, **kwargs):

        query = self.get_query_set().filter(*args, **kwargs)

        if self._select_for_update:

            self._select_for_update = False

            return for_update(query)

        else:

            return query

    def get(self, *args, **kwargs):

        if not self._select_for_update:

            return self.get_query_set().get(*args, **kwargs)

        query = self.filter(*args, **kwargs)

        query = list(query)

        num = len(query)

        if num == 1:

            return query[0]

        if not num:

            raise self.model.DoesNotExist(

                    "%s matching query does not exist. "

                    "Lookup parameters were %s" %

                    (self.model._meta.object_name, kwargs))

        raise self.model.MultipleObjectsReturned(

            "get() returned more than one %s -- it returned %s! "

            "Lookup parameters were %s" %

            (self.model._meta.object_name, num, kwargs))

    def select_for_update(self, *args, **kwargs):

        self._select_for_update = True

        return self

def for_update(query):

    """ Rewrite query using SELECT .. FOR UPDATE.

    """

    if 'sqlite' in connections[query.db].settings_dict['ENGINE'].lower():

        # SQLite  does not support FOR UPDATE

        return query

    sql, params = query.query.get_compiler(query.db).as_sql()

    return query.model._default_manager.raw(sql.rstrip() + ' FOR UPDATE',

                                            params)

class ProtectedDeleteManager(ForUpdateManager):

    """ Manager for protecting Backend deletion.

        Call Backend delete() method in order to prevent deletion

        of Backends that host non-deleted VirtualMachines.

    """

    def get_query_set(self):

        return BackendQuerySet(self.model, using=self._db)

class BackendQuerySet(QuerySet):

    def delete(self):

        for backend in self._clone():

            backend.delete()

from .managers import ForUpdateManager

    objects     =   ForUpdateManager()

    objects     =   ForUpdateManager()

    objects     =   ForUpdateManager()

    objects     =   ForUpdateManager()

    objects     =   ForUpdateManager()

    objects     =   ForUpdateManager()

    objects     =   ForUpdateManager()

def _access(*args, **kwargs):

    method = args[0]

    model = args[1]

    args = args[2:]

    o = model.objects

    try:

        if kwargs['for_update']:

            del kwargs['for_update']

            o = o.select_for_update()

    except KeyError:

        pass

    f = getattr(o, method)

    return f(*args, **kwargs)

def _get(*args, **kwargs):

    return _access('get', *args, **kwargs)

def _filter(*args, **kwargs):

    return _access('filter', *args, **kwargs)

def db_get_holding(*args, **kwargs):

    return _get(Holding, *args, **kwargs)

def db_get_entity(*args, **kwargs):

    return _get(Entity, *args, **kwargs)

def db_get_policy(*args, **kwargs):

    return _get(Policy, *args, **kwargs)

def db_get_commission(*args, **kwargs):

    return _get(Commission, *args, **kwargs)

def db_filter_provision(*args, **kwargs):

    return _filter(Provision, *args, **kwargs)