Refactor pool.py into a package

for better separation of concerns split out the
core pooling constructs from the implementations.  also
makes more room for new pool classes should we decide to
add them.  The DBProxy feature is never used so remove it
from documentation and split it out.

Change-Id: I04c9d7ae1882b17f3cf5c37ed05b781b05ef88fa
Fixes: #4255

1 files changed, 971 insertions, 0 deletions

diff --git a/lib/sqlalchemy/pool/base.py b/lib/sqlalchemy/pool/base.py
new file mode 100644
index 000000000..855110160
--- /dev/null
+++ b/lib/sqlalchemy/pool/base.py
@@ -0,0 +1,971 @@
+# sqlalchemy/pool.py
+# Copyright (C) 2005-2018 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
+
+
+"""Base constructs for connection pools.
+
+"""
+
+from collections import deque
+import time
+import weakref
+
+from .. import exc, log, event, interfaces, util
+from ..util import threading
+
+
+reset_rollback = util.symbol('reset_rollback')
+reset_commit = util.symbol('reset_commit')
+reset_none = util.symbol('reset_none')
+
+
+class _ConnDialect(object):
+
+    """partial implementation of :class:`.Dialect`
+    which provides DBAPI connection methods.
+
+    When a :class:`.Pool` is combined with an :class:`.Engine`,
+    the :class:`.Engine` replaces this with its own
+    :class:`.Dialect`.
+
+    """
+
+    def do_rollback(self, dbapi_connection):
+        dbapi_connection.rollback()
+
+    def do_commit(self, dbapi_connection):
+        dbapi_connection.commit()
+
+    def do_close(self, dbapi_connection):
+        dbapi_connection.close()
+
+    def do_ping(self, dbapi_connection):
+        raise NotImplementedError(
+            "The ping feature requires that a dialect is "
+            "passed to the connection pool.")
+
+
+class Pool(log.Identified):
+
+    """Abstract base class for connection pools."""
+
+    _dialect = _ConnDialect()
+
+    def __init__(self,
+                 creator, recycle=-1, echo=None,
+                 use_threadlocal=False,
+                 logging_name=None,
+                 reset_on_return=True,
+                 listeners=None,
+                 events=None,
+                 dialect=None,
+                 pre_ping=False,
+                 _dispatch=None):
+        """
+        Construct a Pool.
+
+        :param creator: a callable function that returns a DB-API
+          connection object.  The function will be called with
+          parameters.
+
+        :param recycle: If set to non -1, number of seconds between
+          connection recycling, which means upon checkout, if this
+          timeout is surpassed the connection will be closed and
+          replaced with a newly opened connection. Defaults to -1.
+
+        :param logging_name:  String identifier which will be used within
+          the "name" field of logging records generated within the
+          "sqlalchemy.pool" logger. Defaults to a hexstring of the object's
+          id.
+
+        :param echo: If True, connections being pulled and retrieved
+          from the pool will be logged to the standard output, as well
+          as pool sizing information.  Echoing can also be achieved by
+          enabling logging for the "sqlalchemy.pool"
+          namespace. Defaults to False.
+
+        :param use_threadlocal: If set to True, repeated calls to
+          :meth:`connect` within the same application thread will be
+          guaranteed to return the same connection object, if one has
+          already been retrieved from the pool and has not been
+          returned yet.  Offers a slight performance advantage at the
+          cost of individual transactions by default.  The
+          :meth:`.Pool.unique_connection` method is provided to return
+          a consistently unique connection to bypass this behavior
+          when the flag is set.
+
+          .. warning::  The :paramref:`.Pool.use_threadlocal` flag
+             **does not affect the behavior** of :meth:`.Engine.connect`.
+             :meth:`.Engine.connect` makes use of the
+             :meth:`.Pool.unique_connection` method which **does not use thread
+             local context**.  To produce a :class:`.Connection` which refers
+             to the :meth:`.Pool.connect` method, use
+             :meth:`.Engine.contextual_connect`.
+
+             Note that other SQLAlchemy connectivity systems such as
+             :meth:`.Engine.execute` as well as the orm
+             :class:`.Session` make use of
+             :meth:`.Engine.contextual_connect` internally, so these functions
+             are compatible with the :paramref:`.Pool.use_threadlocal` setting.
+
+          .. seealso::
+
+            :ref:`threadlocal_strategy` - contains detail on the
+            "threadlocal" engine strategy, which provides a more comprehensive
+            approach to "threadlocal" connectivity for the specific
+            use case of using :class:`.Engine` and :class:`.Connection` objects
+            directly.
+
+        :param reset_on_return: Determine steps to take on
+          connections as they are returned to the pool.
+          reset_on_return can have any of these values:
+
+          * ``"rollback"`` - call rollback() on the connection,
+            to release locks and transaction resources.
+            This is the default value.  The vast majority
+            of use cases should leave this value set.
+          * ``True`` - same as 'rollback', this is here for
+            backwards compatibility.
+          * ``"commit"`` - call commit() on the connection,
+            to release locks and transaction resources.
+            A commit here may be desirable for databases that
+            cache query plans if a commit is emitted,
+            such as Microsoft SQL Server.  However, this
+            value is more dangerous than 'rollback' because
+            any data changes present on the transaction
+            are committed unconditionally.
+          * ``None`` - don't do anything on the connection.
+            This setting should only be made on a database
+            that has no transaction support at all,
+            namely MySQL MyISAM.   By not doing anything,
+            performance can be improved.   This
+            setting should **never be selected** for a
+            database that supports transactions,
+            as it will lead to deadlocks and stale
+            state.
+          * ``"none"`` - same as ``None``
+
+            .. versionadded:: 0.9.10
+
+          * ``False`` - same as None, this is here for
+            backwards compatibility.
+
+          .. versionchanged:: 0.7.6
+              :paramref:`.Pool.reset_on_return` accepts ``"rollback"``
+              and ``"commit"`` arguments.
+
+        :param events: a list of 2-tuples, each of the form
+         ``(callable, target)`` which will be passed to :func:`.event.listen`
+         upon construction.   Provided here so that event listeners
+         can be assigned via :func:`.create_engine` before dialect-level
+         listeners are applied.
+
+        :param listeners: Deprecated.  A list of
+          :class:`~sqlalchemy.interfaces.PoolListener`-like objects or
+          dictionaries of callables that receive events when DB-API
+          connections are created, checked out and checked in to the
+          pool.  This has been superseded by
+          :func:`~sqlalchemy.event.listen`.
+
+        :param dialect: a :class:`.Dialect` that will handle the job
+         of calling rollback(), close(), or commit() on DBAPI connections.
+         If omitted, a built-in "stub" dialect is used.   Applications that
+         make use of :func:`~.create_engine` should not use this parameter
+         as it is handled by the engine creation strategy.
+
+         .. versionadded:: 1.1 - ``dialect`` is now a public parameter
+            to the :class:`.Pool`.
+
+        :param pre_ping: if True, the pool will emit a "ping" (typically
+         "SELECT 1", but is dialect-specific) on the connection
+         upon checkout, to test if the connection is alive or not.   If not,
+         the connection is transparently re-connected and upon success, all
+         other pooled connections established prior to that timestamp are
+         invalidated.     Requires that a dialect is passed as well to
+         interpret the disconnection error.
+
+         .. versionadded:: 1.2
+
+        """
+        if logging_name:
+            self.logging_name = self._orig_logging_name = logging_name
+        else:
+            self._orig_logging_name = None
+
+        log.instance_logger(self, echoflag=echo)
+        self._threadconns = threading.local()
+        self._creator = creator
+        self._recycle = recycle
+        self._invalidate_time = 0
+        self._use_threadlocal = use_threadlocal
+        self._pre_ping = pre_ping
+        if reset_on_return in ('rollback', True, reset_rollback):
+            self._reset_on_return = reset_rollback
+        elif reset_on_return in ('none', None, False, reset_none):
+            self._reset_on_return = reset_none
+        elif reset_on_return in ('commit', reset_commit):
+            self._reset_on_return = reset_commit
+        else:
+            raise exc.ArgumentError(
+                "Invalid value for 'reset_on_return': %r"
+                % reset_on_return)
+
+        self.echo = echo
+
+        if _dispatch:
+            self.dispatch._update(_dispatch, only_propagate=False)
+        if dialect:
+            self._dialect = dialect
+        if events:
+            for fn, target in events:
+                event.listen(self, target, fn)
+        if listeners:
+            util.warn_deprecated(
+                "The 'listeners' argument to Pool (and "
+                "create_engine()) is deprecated.  Use event.listen().")
+            for l in listeners:
+                self.add_listener(l)
+
+    @property
+    def _creator(self):
+        return self.__dict__['_creator']
+
+    @_creator.setter
+    def _creator(self, creator):
+        self.__dict__['_creator'] = creator
+        self._invoke_creator = self._should_wrap_creator(creator)
+
+    def _should_wrap_creator(self, creator):
+        """Detect if creator accepts a single argument, or is sent
+        as a legacy style no-arg function.
+
+        """
+
+        try:
+            argspec = util.get_callable_argspec(self._creator, no_self=True)
+        except TypeError:
+            return lambda crec: creator()
+
+        defaulted = argspec[3] is not None and len(argspec[3]) or 0
+        positionals = len(argspec[0]) - defaulted
+
+        # look for the exact arg signature that DefaultStrategy
+        # sends us
+        if (argspec[0], argspec[3]) == (['connection_record'], (None,)):
+            return creator
+        # or just a single positional
+        elif positionals == 1:
+            return creator
+        # all other cases, just wrap and assume legacy "creator" callable
+        # thing
+        else:
+            return lambda crec: creator()
+
+    def _close_connection(self, connection):
+        self.logger.debug("Closing connection %r", connection)
+
+        try:
+            self._dialect.do_close(connection)
+        except Exception:
+            self.logger.error("Exception closing connection %r",
+                              connection, exc_info=True)
+
+    @util.deprecated(
+        2.7, "Pool.add_listener is deprecated.  Use event.listen()")
+    def add_listener(self, listener):
+        """Add a :class:`.PoolListener`-like object to this pool.
+
+        ``listener`` may be an object that implements some or all of
+        PoolListener, or a dictionary of callables containing implementations
+        of some or all of the named methods in PoolListener.
+
+        """
+        interfaces.PoolListener._adapt_listener(self, listener)
+
+    def unique_connection(self):
+        """Produce a DBAPI connection that is not referenced by any
+        thread-local context.
+
+        This method is equivalent to :meth:`.Pool.connect` when the
+        :paramref:`.Pool.use_threadlocal` flag is not set to True.
+        When :paramref:`.Pool.use_threadlocal` is True, the
+        :meth:`.Pool.unique_connection` method provides a means of bypassing
+        the threadlocal context.
+
+        """
+        return _ConnectionFairy._checkout(self)
+
+    def _create_connection(self):
+        """Called by subclasses to create a new ConnectionRecord."""
+
+        return _ConnectionRecord(self)
+
+    def _invalidate(self, connection, exception=None, _checkin=True):
+        """Mark all connections established within the generation
+        of the given connection as invalidated.
+
+        If this pool's last invalidate time is before when the given
+        connection was created, update the timestamp til now.  Otherwise,
+        no action is performed.
+
+        Connections with a start time prior to this pool's invalidation
+        time will be recycled upon next checkout.
+        """
+        rec = getattr(connection, "_connection_record", None)
+        if not rec or self._invalidate_time < rec.starttime:
+            self._invalidate_time = time.time()
+        if _checkin and getattr(connection, 'is_valid', False):
+            connection.invalidate(exception)
+
+    def recreate(self):
+        """Return a new :class:`.Pool`, of the same class as this one
+        and configured with identical creation arguments.
+
+        This method is used in conjunction with :meth:`dispose`
+        to close out an entire :class:`.Pool` and create a new one in
+        its place.
+
+        """
+
+        raise NotImplementedError()
+
+    def dispose(self):
+        """Dispose of this pool.
+
+        This method leaves the possibility of checked-out connections
+        remaining open, as it only affects connections that are
+        idle in the pool.
+
+        See also the :meth:`Pool.recreate` method.
+
+        """
+
+        raise NotImplementedError()
+
+    def connect(self):
+        """Return a DBAPI connection from the pool.
+
+        The connection is instrumented such that when its
+        ``close()`` method is called, the connection will be returned to
+        the pool.
+
+        """
+        if not self._use_threadlocal:
+            return _ConnectionFairy._checkout(self)
+
+        try:
+            rec = self._threadconns.current()
+        except AttributeError:
+            pass
+        else:
+            if rec is not None:
+                return rec._checkout_existing()
+
+        return _ConnectionFairy._checkout(self, self._threadconns)
+
+    def _return_conn(self, record):
+        """Given a _ConnectionRecord, return it to the :class:`.Pool`.
+
+        This method is called when an instrumented DBAPI connection
+        has its ``close()`` method called.
+
+        """
+        if self._use_threadlocal:
+            try:
+                del self._threadconns.current
+            except AttributeError:
+                pass
+        self._do_return_conn(record)
+
+    def _do_get(self):
+        """Implementation for :meth:`get`, supplied by subclasses."""
+
+        raise NotImplementedError()
+
+    def _do_return_conn(self, conn):
+        """Implementation for :meth:`return_conn`, supplied by subclasses."""
+
+        raise NotImplementedError()
+
+    def status(self):
+        raise NotImplementedError()
+
+
+class _ConnectionRecord(object):
+
+    """Internal object which maintains an individual DBAPI connection
+    referenced by a :class:`.Pool`.
+
+    The :class:`._ConnectionRecord` object always exists for any particular
+    DBAPI connection whether or not that DBAPI connection has been
+    "checked out".  This is in contrast to the :class:`._ConnectionFairy`
+    which is only a public facade to the DBAPI connection while it is checked
+    out.
+
+    A :class:`._ConnectionRecord` may exist for a span longer than that
+    of a single DBAPI connection.  For example, if the
+    :meth:`._ConnectionRecord.invalidate`
+    method is called, the DBAPI connection associated with this
+    :class:`._ConnectionRecord`
+    will be discarded, but the :class:`._ConnectionRecord` may be used again,
+    in which case a new DBAPI connection is produced when the :class:`.Pool`
+    next uses this record.
+
+    The :class:`._ConnectionRecord` is delivered along with connection
+    pool events, including :meth:`.PoolEvents.connect` and
+    :meth:`.PoolEvents.checkout`, however :class:`._ConnectionRecord` still
+    remains an internal object whose API and internals may change.
+
+    .. seealso::
+
+        :class:`._ConnectionFairy`
+
+    """
+
+    def __init__(self, pool, connect=True):
+        self.__pool = pool
+        if connect:
+            self.__connect(first_connect_check=True)
+        self.finalize_callback = deque()
+
+    fairy_ref = None
+
+    starttime = None
+
+    connection = None
+    """A reference to the actual DBAPI connection being tracked.
+
+    May be ``None`` if this :class:`._ConnectionRecord` has been marked
+    as invalidated; a new DBAPI connection may replace it if the owning
+    pool calls upon this :class:`._ConnectionRecord` to reconnect.
+
+    """
+
+    _soft_invalidate_time = 0
+
+    @util.memoized_property
+    def info(self):
+        """The ``.info`` dictionary associated with the DBAPI connection.
+
+        This dictionary is shared among the :attr:`._ConnectionFairy.info`
+        and :attr:`.Connection.info` accessors.
+
+        .. note::
+
+            The lifespan of this dictionary is linked to the
+            DBAPI connection itself, meaning that it is **discarded** each time
+            the DBAPI connection is closed and/or invalidated.   The
+            :attr:`._ConnectionRecord.record_info` dictionary remains
+            persistent throughout the lifespan of the
+            :class:`._ConnectionRecord` container.
+
+        """
+        return {}
+
+    @util.memoized_property
+    def record_info(self):
+        """An "info' dictionary associated with the connection record
+        itself.
+
+        Unlike the :attr:`._ConnectionRecord.info` dictionary, which is linked
+        to the lifespan of the DBAPI connection, this dictionary is linked
+        to the lifespan of the :class:`._ConnectionRecord` container itself
+        and will remain persisent throughout the life of the
+        :class:`._ConnectionRecord`.
+
+        .. versionadded:: 1.1
+
+        """
+        return {}
+
+    @classmethod
+    def checkout(cls, pool):
+        rec = pool._do_get()
+        try:
+            dbapi_connection = rec.get_connection()
+        except Exception as err:
+            with util.safe_reraise():
+                rec._checkin_failed(err)
+        echo = pool._should_log_debug()
+        fairy = _ConnectionFairy(dbapi_connection, rec, echo)
+        rec.fairy_ref = weakref.ref(
+            fairy,
+            lambda ref: _finalize_fairy and
+            _finalize_fairy(
+                None,
+                rec, pool, ref, echo)
+        )
+        _refs.add(rec)
+        if echo:
+            pool.logger.debug("Connection %r checked out from pool",
+                              dbapi_connection)
+        return fairy
+
+    def _checkin_failed(self, err):
+        self.invalidate(e=err)
+        self.checkin(_no_fairy_ref=True)
+
+    def checkin(self, _no_fairy_ref=False):
+        if self.fairy_ref is None and not _no_fairy_ref:
+            util.warn("Double checkin attempted on %s" % self)
+            return
+        self.fairy_ref = None
+        connection = self.connection
+        pool = self.__pool
+        while self.finalize_callback:
+            finalizer = self.finalize_callback.pop()
+            finalizer(connection)
+        if pool.dispatch.checkin:
+            pool.dispatch.checkin(connection, self)
+        pool._return_conn(self)
+
+    @property
+    def in_use(self):
+        return self.fairy_ref is not None
+
+    @property
+    def last_connect_time(self):
+        return self.starttime
+
+    def close(self):
+        if self.connection is not None:
+            self.__close()
+
+    def invalidate(self, e=None, soft=False):
+        """Invalidate the DBAPI connection held by this :class:`._ConnectionRecord`.
+
+        This method is called for all connection invalidations, including
+        when the :meth:`._ConnectionFairy.invalidate` or
+        :meth:`.Connection.invalidate` methods are called, as well as when any
+        so-called "automatic invalidation" condition occurs.
+
+        :param e: an exception object indicating a reason for the invalidation.
+
+        :param soft: if True, the connection isn't closed; instead, this
+         connection will be recycled on next checkout.
+
+         .. versionadded:: 1.0.3
+
+        .. seealso::
+
+            :ref:`pool_connection_invalidation`
+
+        """
+        # already invalidated
+        if self.connection is None:
+            return
+        if soft:
+            self.__pool.dispatch.soft_invalidate(self.connection, self, e)
+        else:
+            self.__pool.dispatch.invalidate(self.connection, self, e)
+        if e is not None:
+            self.__pool.logger.info(
+                "%sInvalidate connection %r (reason: %s:%s)",
+                "Soft " if soft else "",
+                self.connection, e.__class__.__name__, e)
+        else:
+            self.__pool.logger.info(
+                "%sInvalidate connection %r",
+                "Soft " if soft else "",
+                self.connection)
+        if soft:
+            self._soft_invalidate_time = time.time()
+        else:
+            self.__close()
+            self.connection = None
+
+    def get_connection(self):
+        recycle = False
+        if self.connection is None:
+            self.info.clear()
+            self.__connect()
+        elif self.__pool._recycle > -1 and \
+                time.time() - self.starttime > self.__pool._recycle:
+            self.__pool.logger.info(
+                "Connection %r exceeded timeout; recycling",
+                self.connection)
+            recycle = True
+        elif self.__pool._invalidate_time > self.starttime:
+            self.__pool.logger.info(
+                "Connection %r invalidated due to pool invalidation; " +
+                "recycling",
+                self.connection
+            )
+            recycle = True
+        elif self._soft_invalidate_time > self.starttime:
+            self.__pool.logger.info(
+                "Connection %r invalidated due to local soft invalidation; " +
+                "recycling",
+                self.connection
+            )
+            recycle = True
+
+        if recycle:
+            self.__close()
+            self.info.clear()
+
+            self.__connect()
+        return self.connection
+
+    def __close(self):
+        self.finalize_callback.clear()
+        if self.__pool.dispatch.close:
+            self.__pool.dispatch.close(self.connection, self)
+        self.__pool._close_connection(self.connection)
+        self.connection = None
+
+    def __connect(self, first_connect_check=False):
+        pool = self.__pool
+
+        # ensure any existing connection is removed, so that if
+        # creator fails, this attribute stays None
+        self.connection = None
+        try:
+            self.starttime = time.time()
+            connection = pool._invoke_creator(self)
+            pool.logger.debug("Created new connection %r", connection)
+            self.connection = connection
+        except Exception as e:
+            pool.logger.debug("Error on connect(): %s", e)
+            raise
+        else:
+            if first_connect_check:
+                pool.dispatch.first_connect.\
+                    for_modify(pool.dispatch).\
+                    exec_once(self.connection, self)
+            if pool.dispatch.connect:
+                pool.dispatch.connect(self.connection, self)
+
+
+def _finalize_fairy(connection, connection_record,
+                    pool, ref, echo, fairy=None):
+    """Cleanup for a :class:`._ConnectionFairy` whether or not it's already
+    been garbage collected.
+
+    """
+    _refs.discard(connection_record)
+
+    if ref is not None:
+        if connection_record.fairy_ref is not ref:
+            return
+        assert connection is None
+        connection = connection_record.connection
+
+    if connection is not None:
+        if connection_record and echo:
+            pool.logger.debug("Connection %r being returned to pool",
+                              connection)
+
+        try:
+            fairy = fairy or _ConnectionFairy(
+                connection, connection_record, echo)
+            assert fairy.connection is connection
+            fairy._reset(pool)
+
+            # Immediately close detached instances
+            if not connection_record:
+                if pool.dispatch.close_detached:
+                    pool.dispatch.close_detached(connection)
+                pool._close_connection(connection)
+        except BaseException as e:
+            pool.logger.error(
+                "Exception during reset or similar", exc_info=True)
+            if connection_record:
+                connection_record.invalidate(e=e)
+            if not isinstance(e, Exception):
+                raise
+
+    if connection_record and connection_record.fairy_ref is not None:
+        connection_record.checkin()
+
+
+_refs = set()
+
+
+class _ConnectionFairy(object):
+
+    """Proxies a DBAPI connection and provides return-on-dereference
+    support.
+
+    This is an internal object used by the :class:`.Pool` implementation
+    to provide context management to a DBAPI connection delivered by
+    that :class:`.Pool`.
+
+    The name "fairy" is inspired by the fact that the
+    :class:`._ConnectionFairy` object's lifespan is transitory, as it lasts
+    only for the length of a specific DBAPI connection being checked out from
+    the pool, and additionally that as a transparent proxy, it is mostly
+    invisible.
+
+    .. seealso::
+
+        :class:`._ConnectionRecord`
+
+    """
+
+    def __init__(self, dbapi_connection, connection_record, echo):
+        self.connection = dbapi_connection
+        self._connection_record = connection_record
+        self._echo = echo
+
+    connection = None
+    """A reference to the actual DBAPI connection being tracked."""
+
+    _connection_record = None
+    """A reference to the :class:`._ConnectionRecord` object associated
+    with the DBAPI connection.
+
+    This is currently an internal accessor which is subject to change.
+
+    """
+
+    _reset_agent = None
+    """Refer to an object with a ``.commit()`` and ``.rollback()`` method;
+    if non-None, the "reset-on-return" feature will call upon this object
+    rather than directly against the dialect-level do_rollback() and
+    do_commit() methods.
+
+    In practice, a :class:`.Connection` assigns a :class:`.Transaction` object
+    to this variable when one is in scope so that the :class:`.Transaction`
+    takes the job of committing or rolling back on return if
+    :meth:`.Connection.close` is called while the :class:`.Transaction`
+    still exists.
+
+    This is essentially an "event handler" of sorts but is simplified as an
+    instance variable both for performance/simplicity as well as that there
+    can only be one "reset agent" at a time.
+    """
+
+    @classmethod
+    def _checkout(cls, pool, threadconns=None, fairy=None):
+        if not fairy:
+            fairy = _ConnectionRecord.checkout(pool)
+
+            fairy._pool = pool
+            fairy._counter = 0
+
+            if threadconns is not None:
+                threadconns.current = weakref.ref(fairy)
+
+        if fairy.connection is None:
+            raise exc.InvalidRequestError("This connection is closed")
+        fairy._counter += 1
+
+        if (not pool.dispatch.checkout and not pool._pre_ping) or \
+                fairy._counter != 1:
+            return fairy
+
+        # Pool listeners can trigger a reconnection on checkout, as well
+        # as the pre-pinger.
+        # there are three attempts made here, but note that if the database
+        # is not accessible from a connection standpoint, those won't proceed
+        # here.
+        attempts = 2
+        while attempts > 0:
+            try:
+                if pool._pre_ping:
+                    if fairy._echo:
+                        pool.logger.debug(
+                            "Pool pre-ping on connection %s",
+                            fairy.connection)
+
+                    result = pool._dialect.do_ping(fairy.connection)
+                    if not result:
+                        if fairy._echo:
+                            pool.logger.debug(
+                                "Pool pre-ping on connection %s failed, "
+                                "will invalidate pool", fairy.connection)
+                        raise exc.InvalidatePoolError()
+
+                pool.dispatch.checkout(fairy.connection,
+                                       fairy._connection_record,
+                                       fairy)
+                return fairy
+            except exc.DisconnectionError as e:
+                if e.invalidate_pool:
+                    pool.logger.info(
+                        "Disconnection detected on checkout, "
+                        "invalidating all pooled connections prior to "
+                        "current timestamp (reason: %r)", e)
+                    fairy._connection_record.invalidate(e)
+                    pool._invalidate(fairy, e, _checkin=False)
+                else:
+                    pool.logger.info(
+                        "Disconnection detected on checkout, "
+                        "invalidating individual connection %s (reason: %r)",
+                        fairy.connection, e)
+                    fairy._connection_record.invalidate(e)
+                try:
+                    fairy.connection = \
+                        fairy._connection_record.get_connection()
+                except Exception as err:
+                    with util.safe_reraise():
+                        fairy._connection_record._checkin_failed(err)
+
+                attempts -= 1
+
+        pool.logger.info("Reconnection attempts exhausted on checkout")
+        fairy.invalidate()
+        raise exc.InvalidRequestError("This connection is closed")
+
+    def _checkout_existing(self):
+        return _ConnectionFairy._checkout(self._pool, fairy=self)
+
+    def _checkin(self):
+        _finalize_fairy(self.connection, self._connection_record,
+                        self._pool, None, self._echo, fairy=self)
+        self.connection = None
+        self._connection_record = None
+
+    _close = _checkin
+
+    def _reset(self, pool):
+        if pool.dispatch.reset:
+            pool.dispatch.reset(self, self._connection_record)
+        if pool._reset_on_return is reset_rollback:
+            if self._echo:
+                pool.logger.debug("Connection %s rollback-on-return%s",
+                                  self.connection,
+                                  ", via agent"
+                                  if self._reset_agent else "")
+            if self._reset_agent:
+                self._reset_agent.rollback()
+            else:
+                pool._dialect.do_rollback(self)
+        elif pool._reset_on_return is reset_commit:
+            if self._echo:
+                pool.logger.debug("Connection %s commit-on-return%s",
+                                  self.connection,
+                                  ", via agent"
+                                  if self._reset_agent else "")
+            if self._reset_agent:
+                self._reset_agent.commit()
+            else:
+                pool._dialect.do_commit(self)
+
+    @property
+    def _logger(self):
+        return self._pool.logger
+
+    @property
+    def is_valid(self):
+        """Return True if this :class:`._ConnectionFairy` still refers
+        to an active DBAPI connection."""
+
+        return self.connection is not None
+
+    @util.memoized_property
+    def info(self):
+        """Info dictionary associated with the underlying DBAPI connection
+        referred to by this :class:`.ConnectionFairy`, allowing user-defined
+        data to be associated with the connection.
+
+        The data here will follow along with the DBAPI connection including
+        after it is returned to the connection pool and used again
+        in subsequent instances of :class:`._ConnectionFairy`.  It is shared
+        with the :attr:`._ConnectionRecord.info` and :attr:`.Connection.info`
+        accessors.
+
+        The dictionary associated with a particular DBAPI connection is
+        discarded when the connection itself is discarded.
+
+        """
+        return self._connection_record.info
+
+    @property
+    def record_info(self):
+        """Info dictionary associated with the :class:`._ConnectionRecord
+        container referred to by this :class:`.ConnectionFairy`.
+
+        Unlike the :attr:`._ConnectionFairy.info` dictionary, the lifespan
+        of this dictionary is persistent across connections that are
+        disconnected and/or invalidated within the lifespan of a
+        :class:`._ConnectionRecord`.
+
+        .. versionadded:: 1.1
+
+        """
+        if self._connection_record:
+            return self._connection_record.record_info
+        else:
+            return None
+
+    def invalidate(self, e=None, soft=False):
+        """Mark this connection as invalidated.
+
+        This method can be called directly, and is also called as a result
+        of the :meth:`.Connection.invalidate` method.   When invoked,
+        the DBAPI connection is immediately closed and discarded from
+        further use by the pool.  The invalidation mechanism proceeds
+        via the :meth:`._ConnectionRecord.invalidate` internal method.
+
+        :param e: an exception object indicating a reason for the invalidation.
+
+        :param soft: if True, the connection isn't closed; instead, this
+         connection will be recycled on next checkout.
+
+         .. versionadded:: 1.0.3
+
+        .. seealso::
+
+            :ref:`pool_connection_invalidation`
+
+        """
+
+        if self.connection is None:
+            util.warn("Can't invalidate an already-closed connection.")
+            return
+        if self._connection_record:
+            self._connection_record.invalidate(e=e, soft=soft)
+        if not soft:
+            self.connection = None
+            self._checkin()
+
+    def cursor(self, *args, **kwargs):
+        """Return a new DBAPI cursor for the underlying connection.
+
+        This method is a proxy for the ``connection.cursor()`` DBAPI
+        method.
+
+        """
+        return self.connection.cursor(*args, **kwargs)
+
+    def __getattr__(self, key):
+        return getattr(self.connection, key)
+
+    def detach(self):
+        """Separate this connection from its Pool.
+
+        This means that the connection will no longer be returned to the
+        pool when closed, and will instead be literally closed.  The
+        containing ConnectionRecord is separated from the DB-API connection,
+        and will create a new connection when next used.
+
+        Note that any overall connection limiting constraints imposed by a
+        Pool implementation may be violated after a detach, as the detached
+        connection is removed from the pool's knowledge and control.
+        """
+
+        if self._connection_record is not None:
+            rec = self._connection_record
+            _refs.remove(rec)
+            rec.fairy_ref = None
+            rec.connection = None
+            # TODO: should this be _return_conn?
+            self._pool._do_return_conn(self._connection_record)
+            self.info = self.info.copy()
+            self._connection_record = None
+
+            if self._pool.dispatch.detach:
+                self._pool.dispatch.detach(self.connection, rec)
+
+    def close(self):
+        self._counter -= 1
+        if self._counter == 0:
+            self._checkin()
+
+