calibre-web/vendor/sqlalchemy/engine/threadlocal.py

# engine/threadlocal.py
# Copyright (C) 2005-2013 the SQLAlchemy authors and contributors <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Provides a thread-local transactional wrapper around the root Engine class.

The ``threadlocal`` module is invoked when using the
``strategy="threadlocal"`` flag with :func:`~sqlalchemy.engine.create_engine`.
This module is semi-private and is invoked automatically when the threadlocal
engine strategy is used.
"""

from .. import util
from . import base
import weakref


class TLConnection(base.Connection):

    def __init__(self, *arg, **kw):
        super(TLConnection, self).__init__(*arg, **kw)
        self.__opencount = 0

    def _increment_connect(self):
        self.__opencount += 1
        return self

    def close(self):
        if self.__opencount == 1:
            base.Connection.close(self)
        self.__opencount -= 1

    def _force_close(self):
        self.__opencount = 0
        base.Connection.close(self)


class TLEngine(base.Engine):
    """An Engine that includes support for thread-local managed
    transactions.

    """
    _tl_connection_cls = TLConnection

    def __init__(self, *args, **kwargs):
        super(TLEngine, self).__init__(*args, **kwargs)
        self._connections = util.threading.local()

    def contextual_connect(self, **kw):
        if not hasattr(self._connections, 'conn'):
            connection = None
        else:
            connection = self._connections.conn()

        if connection is None or connection.closed:
            # guards against pool-level reapers, if desired.
            # or not connection.connection.is_valid:
            connection = self._tl_connection_cls(
                self, self.pool.connect(), **kw)
            self._connections.conn = weakref.ref(connection)

        return connection._increment_connect()

    def begin_twophase(self, xid=None):
        if not hasattr(self._connections, 'trans'):
            self._connections.trans = []
        self._connections.trans.append(
            self.contextual_connect().begin_twophase(xid=xid))
        return self

    def begin_nested(self):
        if not hasattr(self._connections, 'trans'):
            self._connections.trans = []
        self._connections.trans.append(
            self.contextual_connect().begin_nested())
        return self

    def begin(self):
        if not hasattr(self._connections, 'trans'):
            self._connections.trans = []
        self._connections.trans.append(self.contextual_connect().begin())
        return self

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        if type is None:
            self.commit()
        else:
            self.rollback()

    def prepare(self):
        if not hasattr(self._connections, 'trans') or \
            not self._connections.trans:
            return
        self._connections.trans[-1].prepare()

    def commit(self):
        if not hasattr(self._connections, 'trans') or \
            not self._connections.trans:
            return
        trans = self._connections.trans.pop(-1)
        trans.commit()

    def rollback(self):
        if not hasattr(self._connections, 'trans') or \
            not self._connections.trans:
            return
        trans = self._connections.trans.pop(-1)
        trans.rollback()

    def dispose(self):
        self._connections = util.threading.local()
        super(TLEngine, self).dispose()

    @property
    def closed(self):
        return not hasattr(self._connections, 'conn') or \
                self._connections.conn() is None or \
                self._connections.conn().closed

    def close(self):
        if not self.closed:
            self.contextual_connect().close()
            connection = self._connections.conn()
            connection._force_close()
            del self._connections.conn
            self._connections.trans = []

    def __repr__(self):
        return 'TLEngine(%s)' % str(self.url)