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# event/registry.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
"""Provides managed registration services on behalf of :func:`.listen`
arguments.
By "managed registration", we mean that event listening functions and
other objects can be added to various collections in such a way that their
membership in all those collections can be revoked at once, based on
an equivalent :class:`._EventKey`.
"""
from __future__ import absolute_import
import collections
import types
import weakref
from .. import exc
from .. import util
_key_to_collection = collections.defaultdict(dict)
"""
Given an original listen() argument, can locate all
listener collections and the listener fn contained
(target, identifier, fn) -> {
ref(listenercollection) -> ref(listener_fn)
ref(listenercollection) -> ref(listener_fn)
ref(listenercollection) -> ref(listener_fn)
}
"""
_collection_to_key = collections.defaultdict(dict)
"""
Given a _ListenerCollection or _ClsLevelListener, can locate
all the original listen() arguments and the listener fn contained
ref(listenercollection) -> {
ref(listener_fn) -> (target, identifier, fn),
ref(listener_fn) -> (target, identifier, fn),
ref(listener_fn) -> (target, identifier, fn),
}
"""
def _collection_gced(ref):
# defaultdict, so can't get a KeyError
if not _collection_to_key or ref not in _collection_to_key:
return
listener_to_key = _collection_to_key.pop(ref)
for key in listener_to_key.values():
if key in _key_to_collection:
# defaultdict, so can't get a KeyError
dispatch_reg = _key_to_collection[key]
dispatch_reg.pop(ref)
if not dispatch_reg:
_key_to_collection.pop(key)
def _stored_in_collection(event_key, owner):
key = event_key._key
dispatch_reg = _key_to_collection[key]
owner_ref = owner.ref
listen_ref = weakref.ref(event_key._listen_fn)
if owner_ref in dispatch_reg:
return False
dispatch_reg[owner_ref] = listen_ref
listener_to_key = _collection_to_key[owner_ref]
listener_to_key[listen_ref] = key
return True
def _removed_from_collection(event_key, owner):
key = event_key._key
dispatch_reg = _key_to_collection[key]
listen_ref = weakref.ref(event_key._listen_fn)
owner_ref = owner.ref
dispatch_reg.pop(owner_ref, None)
if not dispatch_reg:
del _key_to_collection[key]
if owner_ref in _collection_to_key:
listener_to_key = _collection_to_key[owner_ref]
listener_to_key.pop(listen_ref)
def _stored_in_collection_multi(newowner, oldowner, elements):
if not elements:
return
oldowner = oldowner.ref
newowner = newowner.ref
old_listener_to_key = _collection_to_key[oldowner]
new_listener_to_key = _collection_to_key[newowner]
for listen_fn in elements:
listen_ref = weakref.ref(listen_fn)
key = old_listener_to_key[listen_ref]
dispatch_reg = _key_to_collection[key]
if newowner in dispatch_reg:
assert dispatch_reg[newowner] == listen_ref
else:
dispatch_reg[newowner] = listen_ref
new_listener_to_key[listen_ref] = key
def _clear(owner, elements):
if not elements:
return
owner = owner.ref
listener_to_key = _collection_to_key[owner]
for listen_fn in elements:
listen_ref = weakref.ref(listen_fn)
key = listener_to_key[listen_ref]
dispatch_reg = _key_to_collection[key]
dispatch_reg.pop(owner, None)
if not dispatch_reg:
del _key_to_collection[key]
class _EventKey(object):
"""Represent :func:`.listen` arguments."""
__slots__ = (
"target",
"identifier",
"fn",
"fn_key",
"fn_wrap",
"dispatch_target",
)
def __init__(self, target, identifier, fn, dispatch_target, _fn_wrap=None):
self.target = target
self.identifier = identifier
self.fn = fn
if isinstance(fn, types.MethodType):
self.fn_key = id(fn.__func__), id(fn.__self__)
else:
self.fn_key = id(fn)
self.fn_wrap = _fn_wrap
self.dispatch_target = dispatch_target
@property
def _key(self):
return (id(self.target), self.identifier, self.fn_key)
def with_wrapper(self, fn_wrap):
if fn_wrap is self._listen_fn:
return self
else:
return _EventKey(
self.target,
self.identifier,
self.fn,
self.dispatch_target,
_fn_wrap=fn_wrap,
)
def with_dispatch_target(self, dispatch_target):
if dispatch_target is self.dispatch_target:
return self
else:
return _EventKey(
self.target,
self.identifier,
self.fn,
dispatch_target,
_fn_wrap=self.fn_wrap,
)
def listen(self, *args, **kw):
once = kw.pop("once", False)
once_unless_exception = kw.pop("_once_unless_exception", False)
named = kw.pop("named", False)
target, identifier, fn = (
self.dispatch_target,
self.identifier,
self._listen_fn,
)
dispatch_collection = getattr(target.dispatch, identifier)
adjusted_fn = dispatch_collection._adjust_fn_spec(fn, named)
self = self.with_wrapper(adjusted_fn)
stub_function = getattr(
self.dispatch_target.dispatch._events, self.identifier
)
if hasattr(stub_function, "_sa_warn"):
stub_function._sa_warn()
if once or once_unless_exception:
self.with_wrapper(
util.only_once(
self._listen_fn, retry_on_exception=once_unless_exception
)
).listen(*args, **kw)
else:
self.dispatch_target.dispatch._listen(self, *args, **kw)
def remove(self):
key = self._key
if key not in _key_to_collection:
raise exc.InvalidRequestError(
"No listeners found for event %s / %r / %s "
% (self.target, self.identifier, self.fn)
)
dispatch_reg = _key_to_collection.pop(key)
for collection_ref, listener_ref in dispatch_reg.items():
collection = collection_ref()
listener_fn = listener_ref()
if collection is not None and listener_fn is not None:
collection.remove(self.with_wrapper(listener_fn))
def contains(self):
"""Return True if this event key is registered to listen."""
return self._key in _key_to_collection
def base_listen(
self, propagate=False, insert=False, named=False, retval=None
):
target, identifier = self.dispatch_target, self.identifier
dispatch_collection = getattr(target.dispatch, identifier)
if insert:
dispatch_collection.for_modify(target.dispatch).insert(
self, propagate
)
else:
dispatch_collection.for_modify(target.dispatch).append(
self, propagate
)
@property
def _listen_fn(self):
return self.fn_wrap or self.fn
def append_to_list(self, owner, list_):
if _stored_in_collection(self, owner):
list_.append(self._listen_fn)
return True
else:
return False
def remove_from_list(self, owner, list_):
_removed_from_collection(self, owner)
list_.remove(self._listen_fn)
def prepend_to_list(self, owner, list_):
if _stored_in_collection(self, owner):
list_.appendleft(self._listen_fn)
return True
else:
return False
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