from twisted.internet import reactor

from twisted.python.threadpool import ThreadPool

POOL_SIZE=5     #how many threads should the db connector pool should have

dbpool = ThreadPool(minthreads=1, maxthreads=POOL_SIZE, name='database')

dbpool.start()

reactor.addSystemEventTrigger('before', 'shutdown', dbpool.stop)

def run_in_db_thread(f):

    """Decorator to run DB queries in Twisted's thread pool"""

        return threads.deferToThreadPool(reactor, dbpool,f, *args, **kwargs)

class WithSession(object):

    '''a with statement for a database session connection'''

    def __init__(self, engine, autocommit=False):

        self.engine = engine

        self.session = sessionmaker(bind=self.engine)()

    '''a twisted sqlalchemy connector this Decorator adds a session parameter, with a valid session connection'''

    def __init__(self, engine, autocommit=False):

        self.autocommit=autocommit

        self.engine = engine

        @run_in_db_thread

            with WithSession(self.engine, self.autocommit) as session: