Загрузить файлы в «venv/Lib/site-packages/sqlalchemy/pool»

venv/Lib/site-packages/sqlalchemy/pool/__init__.py

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+# pool/__init__.py
+# Copyright (C) 2005-2026 the SQLAlchemy authors and contributors
+# <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: https://www.opensource.org/licenses/mit-license.php
+
+
+"""Connection pooling for DB-API connections.
+
+Provides a number of connection pool implementations for a variety of
+usage scenarios and thread behavior requirements imposed by the
+application, DB-API or database itself.
+
+Also provides a DB-API 2.0 connection proxying mechanism allowing
+regular DB-API connect() methods to be transparently managed by a
+SQLAlchemy connection pool.
+"""
+
+from . import events
+from .base import _AdhocProxiedConnection as _AdhocProxiedConnection
+from .base import _ConnectionFairy as _ConnectionFairy
+from .base import _ConnectionRecord
+from .base import _CreatorFnType as _CreatorFnType
+from .base import _CreatorWRecFnType as _CreatorWRecFnType
+from .base import _finalize_fairy
+from .base import _ResetStyleArgType as _ResetStyleArgType
+from .base import ConnectionPoolEntry as ConnectionPoolEntry
+from .base import ManagesConnection as ManagesConnection
+from .base import Pool as Pool
+from .base import PoolProxiedConnection as PoolProxiedConnection
+from .base import PoolResetState as PoolResetState
+from .base import reset_commit as reset_commit
+from .base import reset_none as reset_none
+from .base import reset_rollback as reset_rollback
+from .impl import AssertionPool as AssertionPool
+from .impl import AsyncAdaptedQueuePool as AsyncAdaptedQueuePool
+from .impl import (
+    FallbackAsyncAdaptedQueuePool as FallbackAsyncAdaptedQueuePool,
+)
+from .impl import NullPool as NullPool
+from .impl import QueuePool as QueuePool
+from .impl import SingletonThreadPool as SingletonThreadPool
+from .impl import StaticPool as StaticPool

venv/Lib/site-packages/sqlalchemy/pool/events.py

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+# pool/events.py
+# Copyright (C) 2005-2026 the SQLAlchemy authors and contributors
+# <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: https://www.opensource.org/licenses/mit-license.php
+from __future__ import annotations
+
+import typing
+from typing import Any
+from typing import Optional
+from typing import Type
+from typing import Union
+
+from .base import ConnectionPoolEntry
+from .base import Pool
+from .base import PoolProxiedConnection
+from .base import PoolResetState
+from .. import event
+from .. import util
+
+if typing.TYPE_CHECKING:
+    from ..engine import Engine
+    from ..engine.interfaces import DBAPIConnection
+
+
+class PoolEvents(event.Events[Pool]):
+    """Available events for :class:`_pool.Pool`.
+
+    The methods here define the name of an event as well
+    as the names of members that are passed to listener
+    functions.
+
+    When using an :class:`.Engine` object created via :func:`_sa.create_engine`
+    (or indirectly via :func:`.create_async_engine`), :class:`.PoolEvents`
+    listeners are expected to be registered in terms of the :class:`.Engine`,
+    which will direct the listeners to the :class:`.Pool` contained within::
+
+        from sqlalchemy import create_engine
+        from sqlalchemy import event
+
+        engine = create_engine("postgresql+psycopg2://scott:tiger@localhost/test")
+
+
+        @event.listens_for(engine, "checkout")
+        def my_on_checkout(dbapi_conn, connection_rec, connection_proxy):
+            "handle an on checkout event"
+
+    :class:`.PoolEvents` may also be registered with the :class:`_pool.Pool`
+    class, with the :class:`.Engine` class, as well as with instances of
+    :class:`_pool.Pool`.
+
+    .. tip::
+
+        Registering :class:`.PoolEvents` with the :class:`.Engine`, if present,
+        is recommended since the :meth:`.Engine.dispose` method will carry
+        along event listeners from the old pool to the new pool.
+
+    """  # noqa: E501
+
+    _target_class_doc = "SomeEngineOrPool"
+    _dispatch_target = Pool
+
+    @util.preload_module("sqlalchemy.engine")
+    @classmethod
+    def _accept_with(
+        cls,
+        target: Union[Pool, Type[Pool], Engine, Type[Engine]],
+        identifier: str,
+    ) -> Optional[Union[Pool, Type[Pool]]]:
+        if not typing.TYPE_CHECKING:
+            Engine = util.preloaded.engine.Engine
+
+        if isinstance(target, type):
+            if issubclass(target, Engine):
+                return Pool
+            else:
+                assert issubclass(target, Pool)
+                return target
+        elif isinstance(target, Engine):
+            return target.pool
+        elif isinstance(target, Pool):
+            return target
+        elif hasattr(target, "_no_async_engine_events"):
+            target._no_async_engine_events()
+        else:
+            return None
+
+    @classmethod
+    def _listen(
+        cls,
+        event_key: event._EventKey[Pool],
+        **kw: Any,
+    ) -> None:
+        target = event_key.dispatch_target
+
+        kw.setdefault("asyncio", target._is_asyncio)
+
+        event_key.base_listen(**kw)
+
+    def connect(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+    ) -> None:
+        """Called at the moment a particular DBAPI connection is first
+        created for a given :class:`_pool.Pool`.
+
+        This event allows one to capture the point directly after which
+        the DBAPI module-level ``.connect()`` method has been used in order
+        to produce a new DBAPI connection.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        """
+
+    def first_connect(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+    ) -> None:
+        """Called exactly once for the first time a DBAPI connection is
+        checked out from a particular :class:`_pool.Pool`.
+
+        The rationale for :meth:`_events.PoolEvents.first_connect`
+        is to determine
+        information about a particular series of database connections based
+        on the settings used for all connections.  Since a particular
+        :class:`_pool.Pool`
+        refers to a single "creator" function (which in terms
+        of a :class:`_engine.Engine`
+        refers to the URL and connection options used),
+        it is typically valid to make observations about a single connection
+        that can be safely assumed to be valid about all subsequent
+        connections, such as the database version, the server and client
+        encoding settings, collation settings, and many others.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        """
+
+    def checkout(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+        connection_proxy: PoolProxiedConnection,
+    ) -> None:
+        """Called when a connection is retrieved from the Pool.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        :param connection_proxy: the :class:`.PoolProxiedConnection` object
+          which will proxy the public interface of the DBAPI connection for the
+          lifespan of the checkout.
+
+        If you raise a :class:`~sqlalchemy.exc.DisconnectionError`, the current
+        connection will be disposed and a fresh connection retrieved.
+        Processing of all checkout listeners will abort and restart
+        using the new connection.
+
+        .. seealso:: :meth:`_events.ConnectionEvents.engine_connect`
+           - a similar event
+           which occurs upon creation of a new :class:`_engine.Connection`.
+
+        """
+
+    def checkin(
+        self,
+        dbapi_connection: Optional[DBAPIConnection],
+        connection_record: ConnectionPoolEntry,
+    ) -> None:
+        """Called when a connection returns to the pool.
+
+        Note that the connection may be closed, and may be None if the
+        connection has been invalidated.  ``checkin`` will not be called
+        for detached connections.  (They do not return to the pool.)
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        """
+
+    @event._legacy_signature(
+        "2.0",
+        ["dbapi_connection", "connection_record"],
+        lambda dbapi_connection, connection_record, reset_state: (
+            dbapi_connection,
+            connection_record,
+        ),
+    )
+    def reset(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+        reset_state: PoolResetState,
+    ) -> None:
+        """Called before the "reset" action occurs for a pooled connection.
+
+        This event represents
+        when the ``rollback()`` method is called on the DBAPI connection
+        before it is returned to the pool or discarded.
+        A custom "reset" strategy may be implemented using this event hook,
+        which may also be combined with disabling the default "reset"
+        behavior using the :paramref:`_pool.Pool.reset_on_return` parameter.
+
+        The primary difference between the :meth:`_events.PoolEvents.reset` and
+        :meth:`_events.PoolEvents.checkin` events are that
+        :meth:`_events.PoolEvents.reset` is called not just for pooled
+        connections that are being returned to the pool, but also for
+        connections that were detached using the
+        :meth:`_engine.Connection.detach` method as well as asyncio connections
+        that are being discarded due to garbage collection taking place on
+        connections before the connection was checked in.
+
+        Note that the event **is not** invoked for connections that were
+        invalidated using :meth:`_engine.Connection.invalidate`.    These
+        events may be intercepted using the :meth:`.PoolEvents.soft_invalidate`
+        and :meth:`.PoolEvents.invalidate` event hooks, and all "connection
+        close" events may be intercepted using :meth:`.PoolEvents.close`.
+
+        The :meth:`_events.PoolEvents.reset` event is usually followed by the
+        :meth:`_events.PoolEvents.checkin` event, except in those
+        cases where the connection is discarded immediately after reset.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        :param reset_state: :class:`.PoolResetState` instance which provides
+         information about the circumstances under which the connection
+         is being reset.
+
+         .. versionadded:: 2.0
+
+        .. seealso::
+
+            :ref:`pool_reset_on_return`
+
+            :meth:`_events.ConnectionEvents.rollback`
+
+            :meth:`_events.ConnectionEvents.commit`
+
+        """
+
+    def invalidate(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+        exception: Optional[BaseException],
+    ) -> None:
+        """Called when a DBAPI connection is to be "invalidated".
+
+        This event is called any time the
+        :meth:`.ConnectionPoolEntry.invalidate` method is invoked, either from
+        API usage or via "auto-invalidation", without the ``soft`` flag.
+
+        The event occurs before a final attempt to call ``.close()`` on the
+        connection occurs.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        :param exception: the exception object corresponding to the reason
+         for this invalidation, if any.  May be ``None``.
+
+        .. seealso::
+
+            :ref:`pool_connection_invalidation`
+
+        """
+
+    def soft_invalidate(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+        exception: Optional[BaseException],
+    ) -> None:
+        """Called when a DBAPI connection is to be "soft invalidated".
+
+        This event is called any time the
+        :meth:`.ConnectionPoolEntry.invalidate`
+        method is invoked with the ``soft`` flag.
+
+        Soft invalidation refers to when the connection record that tracks
+        this connection will force a reconnect after the current connection
+        is checked in.   It does not actively close the dbapi_connection
+        at the point at which it is called.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        :param exception: the exception object corresponding to the reason
+         for this invalidation, if any.  May be ``None``.
+
+        """
+
+    def close(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+    ) -> None:
+        """Called when a DBAPI connection is closed.
+
+        The event is emitted before the close occurs.
+
+        The close of a connection can fail; typically this is because
+        the connection is already closed.  If the close operation fails,
+        the connection is discarded.
+
+        The :meth:`.close` event corresponds to a connection that's still
+        associated with the pool. To intercept close events for detached
+        connections use :meth:`.close_detached`.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        """
+
+    def detach(
+        self,
+        dbapi_connection: DBAPIConnection,
+        connection_record: ConnectionPoolEntry,
+    ) -> None:
+        """Called when a DBAPI connection is "detached" from a pool.
+
+        This event is emitted after the detach occurs.  The connection
+        is no longer associated with the given connection record.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        :param connection_record: the :class:`.ConnectionPoolEntry` managing
+         the DBAPI connection.
+
+        """
+
+    def close_detached(self, dbapi_connection: DBAPIConnection) -> None:
+        """Called when a detached DBAPI connection is closed.
+
+        The event is emitted before the close occurs.
+
+        The close of a connection can fail; typically this is because
+        the connection is already closed.  If the close operation fails,
+        the connection is discarded.
+
+        :param dbapi_connection: a DBAPI connection.
+         The :attr:`.ConnectionPoolEntry.dbapi_connection` attribute.
+
+        """

venv/Lib/site-packages/sqlalchemy/pool/impl.py

@@ -0,0 +1,589 @@
+# pool/impl.py
+# Copyright (C) 2005-2026 the SQLAlchemy authors and contributors
+# <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: https://www.opensource.org/licenses/mit-license.php
+
+
+"""Pool implementation classes."""
+
+from __future__ import annotations
+
+import threading
+import traceback
+import typing
+from typing import Any
+from typing import cast
+from typing import List
+from typing import Optional
+from typing import Set
+from typing import Type
+from typing import TYPE_CHECKING
+from typing import Union
+import weakref
+
+from .base import _AsyncConnDialect
+from .base import _ConnectionFairy
+from .base import _ConnectionRecord
+from .base import _CreatorFnType
+from .base import _CreatorWRecFnType
+from .base import ConnectionPoolEntry
+from .base import Pool
+from .base import PoolProxiedConnection
+from .. import exc
+from .. import util
+from ..util import chop_traceback
+from ..util import queue as sqla_queue
+from ..util.typing import Literal
+
+if typing.TYPE_CHECKING:
+    from ..engine.interfaces import DBAPIConnection
+
+
+class QueuePool(Pool):
+    """A :class:`_pool.Pool`
+    that imposes a limit on the number of open connections.
+
+    :class:`.QueuePool` is the default pooling implementation used for
+    all :class:`_engine.Engine` objects other than SQLite with a ``:memory:``
+    database.
+
+    The :class:`.QueuePool` class **is not compatible** with asyncio and
+    :func:`_asyncio.create_async_engine`.  The
+    :class:`.AsyncAdaptedQueuePool` class is used automatically when
+    using :func:`_asyncio.create_async_engine`, if no other kind of pool
+    is specified.
+
+    .. seealso::
+
+        :class:`.AsyncAdaptedQueuePool`
+
+    """
+
+    _is_asyncio = False
+
+    _queue_class: Type[sqla_queue.QueueCommon[ConnectionPoolEntry]] = (
+        sqla_queue.Queue
+    )
+
+    _pool: sqla_queue.QueueCommon[ConnectionPoolEntry]
+
+    def __init__(
+        self,
+        creator: Union[_CreatorFnType, _CreatorWRecFnType],
+        pool_size: int = 5,
+        max_overflow: int = 10,
+        timeout: float = 30.0,
+        use_lifo: bool = False,
+        **kw: Any,
+    ):
+        r"""
+        Construct a QueuePool.
+
+        :param creator: a callable function that returns a DB-API
+          connection object, same as that of :paramref:`_pool.Pool.creator`.
+
+        :param pool_size: The size of the pool to be maintained,
+          defaults to 5. This is the largest number of connections that
+          will be kept persistently in the pool. Note that the pool
+          begins with no connections; once this number of connections
+          is requested, that number of connections will remain.
+          ``pool_size`` can be set to 0 to indicate no size limit; to
+          disable pooling, use a :class:`~sqlalchemy.pool.NullPool`
+          instead.
+
+        :param max_overflow: The maximum overflow size of the
+          pool. When the number of checked-out connections reaches the
+          size set in pool_size, additional connections will be
+          returned up to this limit. When those additional connections
+          are returned to the pool, they are disconnected and
+          discarded. It follows then that the total number of
+          simultaneous connections the pool will allow is pool_size +
+          `max_overflow`, and the total number of "sleeping"
+          connections the pool will allow is pool_size. `max_overflow`
+          can be set to -1 to indicate no overflow limit; no limit
+          will be placed on the total number of concurrent
+          connections. Defaults to 10.
+
+        :param timeout: The number of seconds to wait before giving up
+          on returning a connection. Defaults to 30.0. This can be a float
+          but is subject to the limitations of Python time functions which
+          may not be reliable in the tens of milliseconds.
+
+        :param use_lifo: use LIFO (last-in-first-out) when retrieving
+          connections instead of FIFO (first-in-first-out). Using LIFO, a
+          server-side timeout scheme can reduce the number of connections used
+          during non-peak periods of use.   When planning for server-side
+          timeouts, ensure that a recycle or pre-ping strategy is in use to
+          gracefully handle stale connections.
+
+          .. versionadded:: 1.3
+
+          .. seealso::
+
+            :ref:`pool_use_lifo`
+
+            :ref:`pool_disconnects`
+
+        :param \**kw: Other keyword arguments including
+          :paramref:`_pool.Pool.recycle`, :paramref:`_pool.Pool.echo`,
+          :paramref:`_pool.Pool.reset_on_return` and others are passed to the
+          :class:`_pool.Pool` constructor.
+
+        """
+
+        Pool.__init__(self, creator, **kw)
+        self._pool = self._queue_class(pool_size, use_lifo=use_lifo)
+        self._overflow = 0 - pool_size
+        self._max_overflow = -1 if pool_size == 0 else max_overflow
+        self._timeout = timeout
+        self._overflow_lock = threading.Lock()
+
+    def _do_return_conn(self, record: ConnectionPoolEntry) -> None:
+        try:
+            self._pool.put(record, False)
+        except sqla_queue.Full:
+            try:
+                record.close()
+            finally:
+                self._dec_overflow()
+
+    def _do_get(self) -> ConnectionPoolEntry:
+        use_overflow = self._max_overflow > -1
+
+        wait = use_overflow and self._overflow >= self._max_overflow
+        try:
+            return self._pool.get(wait, self._timeout)
+        except sqla_queue.Empty:
+            # don't do things inside of "except Empty", because when we say
+            # we timed out or can't connect and raise, Python 3 tells
+            # people the real error is queue.Empty which it isn't.
+            pass
+        if use_overflow and self._overflow >= self._max_overflow:
+            if not wait:
+                return self._do_get()
+            else:
+                raise exc.TimeoutError(
+                    "QueuePool limit of size %d overflow %d reached, "
+                    "connection timed out, timeout %0.2f"
+                    % (self.size(), self.overflow(), self._timeout),
+                    code="3o7r",
+                )
+
+        if self._inc_overflow():
+            try:
+                return self._create_connection()
+            except:
+                with util.safe_reraise():
+                    self._dec_overflow()
+                raise
+        else:
+            return self._do_get()
+
+    def _inc_overflow(self) -> bool:
+        if self._max_overflow == -1:
+            self._overflow += 1
+            return True
+        with self._overflow_lock:
+            if self._overflow < self._max_overflow:
+                self._overflow += 1
+                return True
+            else:
+                return False
+
+    def _dec_overflow(self) -> Literal[True]:
+        if self._max_overflow == -1:
+            self._overflow -= 1
+            return True
+        with self._overflow_lock:
+            self._overflow -= 1
+            return True
+
+    def recreate(self) -> QueuePool:
+        self.logger.info("Pool recreating")
+        return self.__class__(
+            self._creator,
+            pool_size=self._pool.maxsize,
+            max_overflow=self._max_overflow,
+            pre_ping=self._pre_ping,
+            use_lifo=self._pool.use_lifo,
+            timeout=self._timeout,
+            recycle=self._recycle,
+            echo=self.echo,
+            logging_name=self._orig_logging_name,
+            reset_on_return=self._reset_on_return,
+            _dispatch=self.dispatch,
+            dialect=self._dialect,
+        )
+
+    def dispose(self) -> None:
+        while True:
+            try:
+                conn = self._pool.get(False)
+                conn.close()
+            except sqla_queue.Empty:
+                break
+
+        self._overflow = 0 - self.size()
+        self.logger.info("Pool disposed. %s", self.status())
+
+    def status(self) -> str:
+        return (
+            "Pool size: %d  Connections in pool: %d "
+            "Current Overflow: %d Current Checked out "
+            "connections: %d"
+            % (
+                self.size(),
+                self.checkedin(),
+                self.overflow(),
+                self.checkedout(),
+            )
+        )
+
+    def size(self) -> int:
+        return self._pool.maxsize
+
+    def timeout(self) -> float:
+        return self._timeout
+
+    def checkedin(self) -> int:
+        return self._pool.qsize()
+
+    def overflow(self) -> int:
+        return self._overflow if self._pool.maxsize else 0
+
+    def checkedout(self) -> int:
+        return self._pool.maxsize - self._pool.qsize() + self._overflow
+
+
+class AsyncAdaptedQueuePool(QueuePool):
+    """An asyncio-compatible version of :class:`.QueuePool`.
+
+    This pool is used by default when using :class:`.AsyncEngine` engines that
+    were generated from :func:`_asyncio.create_async_engine`.   It uses an
+    asyncio-compatible queue implementation that does not use
+    ``threading.Lock``.
+
+    The arguments and operation of :class:`.AsyncAdaptedQueuePool` are
+    otherwise identical to that of :class:`.QueuePool`.
+
+    """
+
+    _is_asyncio = True
+    _queue_class: Type[sqla_queue.QueueCommon[ConnectionPoolEntry]] = (
+        sqla_queue.AsyncAdaptedQueue
+    )
+
+    _dialect = _AsyncConnDialect()
+
+
+class FallbackAsyncAdaptedQueuePool(AsyncAdaptedQueuePool):
+    _queue_class = sqla_queue.FallbackAsyncAdaptedQueue  # type: ignore[assignment] # noqa: E501
+
+
+class NullPool(Pool):
+    """A Pool which does not pool connections.
+
+    Instead it literally opens and closes the underlying DB-API connection
+    per each connection open/close.
+
+    Reconnect-related functions such as ``recycle`` and connection
+    invalidation are not supported by this Pool implementation, since
+    no connections are held persistently.
+
+    The :class:`.NullPool` class **is compatible** with asyncio and
+    :func:`_asyncio.create_async_engine`.
+
+    """
+
+    def status(self) -> str:
+        return "NullPool"
+
+    def _do_return_conn(self, record: ConnectionPoolEntry) -> None:
+        record.close()
+
+    def _do_get(self) -> ConnectionPoolEntry:
+        return self._create_connection()
+
+    def recreate(self) -> NullPool:
+        self.logger.info("Pool recreating")
+
+        return self.__class__(
+            self._creator,
+            recycle=self._recycle,
+            echo=self.echo,
+            logging_name=self._orig_logging_name,
+            reset_on_return=self._reset_on_return,
+            pre_ping=self._pre_ping,
+            _dispatch=self.dispatch,
+            dialect=self._dialect,
+        )
+
+    def dispose(self) -> None:
+        pass
+
+
+class SingletonThreadPool(Pool):
+    """A Pool that maintains one connection per thread.
+
+    Maintains one connection per each thread, never moving a connection to a
+    thread other than the one which it was created in.
+
+    .. warning::  the :class:`.SingletonThreadPool` will call ``.close()``
+       on arbitrary connections that exist beyond the size setting of
+       ``pool_size``, e.g. if more unique **thread identities**
+       than what ``pool_size`` states are used.   This cleanup is
+       non-deterministic and not sensitive to whether or not the connections
+       linked to those thread identities are currently in use.
+
+       :class:`.SingletonThreadPool` may be improved in a future release,
+       however in its current status it is generally used only for test
+       scenarios using a SQLite ``:memory:`` database and is not recommended
+       for production use.
+
+    The :class:`.SingletonThreadPool` class **is not compatible** with asyncio
+    and :func:`_asyncio.create_async_engine`.
+
+
+    Options are the same as those of :class:`_pool.Pool`, as well as:
+
+    :param pool_size: The number of threads in which to maintain connections
+        at once.  Defaults to five.
+
+    :class:`.SingletonThreadPool` is used by the SQLite dialect
+    automatically when a memory-based database is used.
+    See :ref:`sqlite_toplevel`.
+
+    """
+
+    _is_asyncio = False
+
+    def __init__(
+        self,
+        creator: Union[_CreatorFnType, _CreatorWRecFnType],
+        pool_size: int = 5,
+        **kw: Any,
+    ):
+        Pool.__init__(self, creator, **kw)
+        self._conn = threading.local()
+        self._fairy = threading.local()
+        self._all_conns: Set[ConnectionPoolEntry] = set()
+        self.size = pool_size
+
+    def recreate(self) -> SingletonThreadPool:
+        self.logger.info("Pool recreating")
+        return self.__class__(
+            self._creator,
+            pool_size=self.size,
+            recycle=self._recycle,
+            echo=self.echo,
+            pre_ping=self._pre_ping,
+            logging_name=self._orig_logging_name,
+            reset_on_return=self._reset_on_return,
+            _dispatch=self.dispatch,
+            dialect=self._dialect,
+        )
+
+    def _transfer_from(
+        self, other_singleton_pool: SingletonThreadPool
+    ) -> None:
+        # used by the test suite to make a new engine / pool without
+        # losing the state of an existing SQLite :memory: connection
+        assert not hasattr(other_singleton_pool._fairy, "current")
+        self._conn = other_singleton_pool._conn
+        self._all_conns = other_singleton_pool._all_conns
+
+    def dispose(self) -> None:
+        """Dispose of this pool."""
+
+        for conn in self._all_conns:
+            try:
+                conn.close()
+            except Exception:
+                # pysqlite won't even let you close a conn from a thread
+                # that didn't create it
+                pass
+
+        self._all_conns.clear()
+
+    def _cleanup(self) -> None:
+        while len(self._all_conns) >= self.size:
+            c = self._all_conns.pop()
+            c.close()
+
+    def status(self) -> str:
+        return "SingletonThreadPool id:%d size: %d" % (
+            id(self),
+            len(self._all_conns),
+        )
+
+    def _do_return_conn(self, record: ConnectionPoolEntry) -> None:
+        try:
+            del self._fairy.current
+        except AttributeError:
+            pass
+
+    def _do_get(self) -> ConnectionPoolEntry:
+        try:
+            if TYPE_CHECKING:
+                c = cast(ConnectionPoolEntry, self._conn.current())
+            else:
+                c = self._conn.current()
+            if c:
+                return c
+        except AttributeError:
+            pass
+        c = self._create_connection()
+        self._conn.current = weakref.ref(c)
+        if len(self._all_conns) >= self.size:
+            self._cleanup()
+        self._all_conns.add(c)
+        return c
+
+    def connect(self) -> PoolProxiedConnection:
+        # vendored from Pool to include the now removed use_threadlocal
+        # behavior
+        try:
+            rec = cast(_ConnectionFairy, self._fairy.current())
+        except AttributeError:
+            pass
+        else:
+            if rec is not None:
+                return rec._checkout_existing()
+
+        return _ConnectionFairy._checkout(self, self._fairy)
+
+
+class StaticPool(Pool):
+    """A Pool of exactly one connection, used for all requests.
+
+    Reconnect-related functions such as ``recycle`` and connection
+    invalidation (which is also used to support auto-reconnect) are only
+    partially supported right now and may not yield good results.
+
+    The :class:`.StaticPool` class **is compatible** with asyncio and
+    :func:`_asyncio.create_async_engine`.
+
+    """
+
+    @util.memoized_property
+    def connection(self) -> _ConnectionRecord:
+        return _ConnectionRecord(self)
+
+    def status(self) -> str:
+        return "StaticPool"
+
+    def dispose(self) -> None:
+        if (
+            "connection" in self.__dict__
+            and self.connection.dbapi_connection is not None
+        ):
+            self.connection.close()
+            del self.__dict__["connection"]
+
+    def recreate(self) -> StaticPool:
+        self.logger.info("Pool recreating")
+        return self.__class__(
+            creator=self._creator,
+            recycle=self._recycle,
+            reset_on_return=self._reset_on_return,
+            pre_ping=self._pre_ping,
+            echo=self.echo,
+            logging_name=self._orig_logging_name,
+            _dispatch=self.dispatch,
+            dialect=self._dialect,
+        )
+
+    def _transfer_from(self, other_static_pool: StaticPool) -> None:
+        # used by the test suite to make a new engine / pool without
+        # losing the state of an existing SQLite :memory: connection
+        def creator(rec: ConnectionPoolEntry) -> DBAPIConnection:
+            conn = other_static_pool.connection.dbapi_connection
+            assert conn is not None
+            return conn
+
+        self._invoke_creator = creator
+
+    def _create_connection(self) -> ConnectionPoolEntry:
+        raise NotImplementedError()
+
+    def _do_return_conn(self, record: ConnectionPoolEntry) -> None:
+        pass
+
+    def _do_get(self) -> ConnectionPoolEntry:
+        rec = self.connection
+        if rec._is_hard_or_soft_invalidated():
+            del self.__dict__["connection"]
+            rec = self.connection
+
+        return rec
+
+
+class AssertionPool(Pool):
+    """A :class:`_pool.Pool` that allows at most one checked out connection at
+    any given time.
+
+    This will raise an exception if more than one connection is checked out
+    at a time.  Useful for debugging code that is using more connections
+    than desired.
+
+    The :class:`.AssertionPool` class **is compatible** with asyncio and
+    :func:`_asyncio.create_async_engine`.
+
+    """
+
+    _conn: Optional[ConnectionPoolEntry]
+    _checkout_traceback: Optional[List[str]]
+
+    def __init__(self, *args: Any, **kw: Any):
+        self._conn = None
+        self._checked_out = False
+        self._store_traceback = kw.pop("store_traceback", True)
+        self._checkout_traceback = None
+        Pool.__init__(self, *args, **kw)
+
+    def status(self) -> str:
+        return "AssertionPool"
+
+    def _do_return_conn(self, record: ConnectionPoolEntry) -> None:
+        if not self._checked_out:
+            raise AssertionError("connection is not checked out")
+        self._checked_out = False
+        assert record is self._conn
+
+    def dispose(self) -> None:
+        self._checked_out = False
+        if self._conn:
+            self._conn.close()
+
+    def recreate(self) -> AssertionPool:
+        self.logger.info("Pool recreating")
+        return self.__class__(
+            self._creator,
+            echo=self.echo,
+            pre_ping=self._pre_ping,
+            recycle=self._recycle,
+            reset_on_return=self._reset_on_return,
+            logging_name=self._orig_logging_name,
+            _dispatch=self.dispatch,
+            dialect=self._dialect,
+        )
+
+    def _do_get(self) -> ConnectionPoolEntry:
+        if self._checked_out:
+            if self._checkout_traceback:
+                suffix = " at:\n%s" % "".join(
+                    chop_traceback(self._checkout_traceback)
+                )
+            else:
+                suffix = ""
+            raise AssertionError("connection is already checked out" + suffix)
+
+        if not self._conn:
+            self._conn = self._create_connection()
+
+        self._checked_out = True
+        if self._store_traceback:
+            self._checkout_traceback = traceback.format_stack()
+        return self._conn