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base.py
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# sqlalchemy/pool.py # Copyright (C) 2005-2021 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 event from .. import exc from .. import interfaces from .. import log from .. import 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.Pool` is combined with an :class:`_engine.Engine`, the :class:`_engine.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() @util.deprecated_params( use_threadlocal=( "1.3", "The :paramref:`_pool.Pool.use_threadlocal` parameter is " "deprecated and will be removed in a future release.", ), listeners=( "0.7", ":class:`.PoolListener` is deprecated in favor of the " ":class:`_events.PoolEvents` listener interface. The " ":paramref:`_pool.Pool.listeners` parameter will be removed in a " "future release.", ), ) 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 a value other than -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, the connection pool will log informational output such as when connections are invalidated as well as when connections are recycled to the default log handler, which defaults to ``sys.stdout`` for output.. If set to the string ``"debug"``, the logging will include pool checkouts and checkins. The :paramref:`_pool.Pool.echo` parameter can also be set from the :func:`_sa.create_engine` call by using the :paramref:`_sa.create_engine.echo_pool` parameter. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :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 that is already checked out. This is a legacy use case and the flag has no effect when using the pool with a :class:`_engine.Engine` object. :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 generally only be made on a database that has no transaction support at all, namely MySQL MyISAM; when used on this backend, performance can be improved as the "rollback" call is still expensive on MySQL. It is **strongly recommended** that this setting not be used for transaction-supporting databases in conjunction with a persistent pool such as :class:`.QueuePool`, as it opens the possibility for connections still in a transaction to be idle in the pool. The setting may be appropriate in the case of :class:`.NullPool` or special circumstances where the connection pool in use is not being used to maintain connection lifecycle. * ``False`` - same as None, this is here for backwards compatibility. :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:`_sa.create_engine` before dialect-level listeners are applied. :param listeners: A list of :class:`.PoolListener`-like objects or dictionaries of callables that receive events when DB-API connections are created, checked out and checked in to the pool. :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:`_sa.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.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 self._reset_on_return = util.symbol.parse_user_argument( reset_on_return, { reset_rollback: ["rollback", True], reset_none: ["none", None, False], reset_commit: ["commit"], }, "reset_on_return", resolve_symbol_names=False, ) 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: 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( "0.7", "The :meth:`_pool.Pool.add_listener` method is deprecated and " "will be removed in a future release. Please use the " ":class:`_events.PoolEvents` listener interface.", ) 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.Pool.connect` when the :paramref:`_pool.Pool.use_threadlocal` flag is not set to True. When :paramref:`_pool.Pool.use_threadlocal` is True, the :meth:`_pool.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.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.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. .. seealso:: :meth:`Pool.recreate` """ 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.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.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.Pool` next uses this record. The :class:`._ConnectionRecord` is delivered along with connection pool events, including :meth:`_events.PoolEvents.connect` and :meth:`_events.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:`_engine.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 persistent 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:`_engine.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 # NOTE: the various comparisons here are assuming that measurable time # passes between these state changes. however, time.time() is not # guaranteed to have sub-second precision. comparisons of # "invalidation time" to "starttime" should perhaps use >= so that the # state change can take place assuming no measurable time has passed, # however this does not guarantee correct behavior here as if time # continues to not pass, it will try to reconnect repeatedly until # these timestamps diverge, so in that sense using > is safer. Per # https://stackoverflow.com/a/1938096/34549, Windows time.time() may be # within 16 milliseconds accuracy, so unit tests for connection # invalidation need a sleep of at least this long between initial start # time and invalidation for the logic below to work reliably. 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: with util.safe_reraise(): pool.logger.debug("Error on connect(): %s", e) else: if first_connect_check: pool.dispatch.first_connect.for_modify( pool.dispatch ).exec_once_unless_exception(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.Pool` implementation to provide context management to a DBAPI connection delivered by that :class:`_pool.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:`_engine.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:`_engine.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: if not self._reset_agent.is_active: util.warn( "Reset agent is not active. " "This should not occur unless there was already " "a connectivity error in progress." ) pool._dialect.do_rollback(self) else: 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: if not self._reset_agent.is_active: util.warn( "Reset agent is not active. " "This should not occur unless there was already " "a connectivity error in progress." ) pool._dialect.do_commit(self) else: 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:`_engine.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:`_engine.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()