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attr.py
# event/attr.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 """Attribute implementation for _Dispatch classes. The various listener targets for a particular event class are represented as attributes, which refer to collections of listeners to be fired off. These collections can exist at the class level as well as at the instance level. An event is fired off using code like this:: some_object.dispatch.first_connect(arg1, arg2) Above, ``some_object.dispatch`` would be an instance of ``_Dispatch`` and ``first_connect`` is typically an instance of ``_ListenerCollection`` if event listeners are present, or ``_EmptyListener`` if none are present. The attribute mechanics here spend effort trying to ensure listener functions are available with a minimum of function call overhead, that unnecessary objects aren't created (i.e. many empty per-instance listener collections), as well as that everything is garbage collectable when owning references are lost. Other features such as "propagation" of listener functions across many ``_Dispatch`` instances, "joining" of multiple ``_Dispatch`` instances, as well as support for subclass propagation (e.g. events assigned to ``Pool`` vs. ``QueuePool``) are all implemented here. """ from __future__ import absolute_import from __future__ import with_statement import collections from itertools import chain import weakref from . import legacy from . import registry from .. import exc from .. import util from ..util import threading class RefCollection(util.MemoizedSlots): __slots__ = ("ref",) def _memoized_attr_ref(self): return weakref.ref(self, registry._collection_gced) class _empty_collection(object): def append(self, element): pass def extend(self, other): pass def remove(self, element): pass def __iter__(self): return iter([]) def clear(self): pass class _ClsLevelDispatch(RefCollection): """Class-level events on :class:`._Dispatch` classes.""" __slots__ = ( "name", "arg_names", "has_kw", "legacy_signatures", "_clslevel", "__weakref__", ) def __init__(self, parent_dispatch_cls, fn): self.name = fn.__name__ argspec = util.inspect_getfullargspec(fn) self.arg_names = argspec.args[1:] self.has_kw = bool(argspec.varkw) self.legacy_signatures = list( reversed( sorted( getattr(fn, "_legacy_signatures", []), key=lambda s: s[0] ) ) ) fn.__doc__ = legacy._augment_fn_docs(self, parent_dispatch_cls, fn) self._clslevel = weakref.WeakKeyDictionary() def _adjust_fn_spec(self, fn, named): if named: fn = self._wrap_fn_for_kw(fn) if self.legacy_signatures: try: argspec = util.get_callable_argspec(fn, no_self=True) except TypeError: pass else: fn = legacy._wrap_fn_for_legacy(self, fn, argspec) return fn def _wrap_fn_for_kw(self, fn): def wrap_kw(*args, **kw): argdict = dict(zip(self.arg_names, args)) argdict.update(kw) return fn(**argdict) return wrap_kw def insert(self, event_key, propagate): target = event_key.dispatch_target assert isinstance( target, type ), "Class-level Event targets must be classes." if not getattr(target, "_sa_propagate_class_events", True): raise exc.InvalidRequestError( "Can't assign an event directly to the %s class" % target ) stack = [target] while stack: cls = stack.pop(0) stack.extend(cls.__subclasses__()) if cls is not target and cls not in self._clslevel: self.update_subclass(cls) else: if cls not in self._clslevel: self._assign_cls_collection(cls) self._clslevel[cls].appendleft(event_key._listen_fn) registry._stored_in_collection(event_key, self) def append(self, event_key, propagate): target = event_key.dispatch_target assert isinstance( target, type ), "Class-level Event targets must be classes." if not getattr(target, "_sa_propagate_class_events", True): raise exc.InvalidRequestError( "Can't assign an event directly to the %s class" % target ) stack = [target] while stack: cls = stack.pop(0) stack.extend(cls.__subclasses__()) if cls is not target and cls not in self._clslevel: self.update_subclass(cls) else: if cls not in self._clslevel: self._assign_cls_collection(cls) self._clslevel[cls].append(event_key._listen_fn) registry._stored_in_collection(event_key, self) def _assign_cls_collection(self, target): if getattr(target, "_sa_propagate_class_events", True): self._clslevel[target] = collections.deque() else: self._clslevel[target] = _empty_collection() def update_subclass(self, target): if target not in self._clslevel: self._assign_cls_collection(target) clslevel = self._clslevel[target] for cls in target.__mro__[1:]: if cls in self._clslevel: clslevel.extend( [fn for fn in self._clslevel[cls] if fn not in clslevel] ) def remove(self, event_key): target = event_key.dispatch_target stack = [target] while stack: cls = stack.pop(0) stack.extend(cls.__subclasses__()) if cls in self._clslevel: self._clslevel[cls].remove(event_key._listen_fn) registry._removed_from_collection(event_key, self) def clear(self): """Clear all class level listeners""" to_clear = set() for dispatcher in self._clslevel.values(): to_clear.update(dispatcher) dispatcher.clear() registry._clear(self, to_clear) def for_modify(self, obj): """Return an event collection which can be modified. For _ClsLevelDispatch at the class level of a dispatcher, this returns self. """ return self class _InstanceLevelDispatch(RefCollection): __slots__ = () def _adjust_fn_spec(self, fn, named): return self.parent._adjust_fn_spec(fn, named) class _EmptyListener(_InstanceLevelDispatch): """Serves as a proxy interface to the events served by a _ClsLevelDispatch, when there are no instance-level events present. Is replaced by _ListenerCollection when instance-level events are added. """ propagate = frozenset() listeners = () __slots__ = "parent", "parent_listeners", "name" def __init__(self, parent, target_cls): if target_cls not in parent._clslevel: parent.update_subclass(target_cls) self.parent = parent # _ClsLevelDispatch self.parent_listeners = parent._clslevel[target_cls] self.name = parent.name def for_modify(self, obj): """Return an event collection which can be modified. For _EmptyListener at the instance level of a dispatcher, this generates a new _ListenerCollection, applies it to the instance, and returns it. """ result = _ListenerCollection(self.parent, obj._instance_cls) if getattr(obj, self.name) is self: setattr(obj, self.name, result) else: assert isinstance(getattr(obj, self.name), _JoinedListener) return result def _needs_modify(self, *args, **kw): raise NotImplementedError("need to call for_modify()") exec_once = ( exec_once_unless_exception ) = insert = append = remove = clear = _needs_modify def __call__(self, *args, **kw): """Execute this event.""" for fn in self.parent_listeners: fn(*args, **kw) def __len__(self): return len(self.parent_listeners) def __iter__(self): return iter(self.parent_listeners) def __bool__(self): return bool(self.parent_listeners) __nonzero__ = __bool__ class _CompoundListener(_InstanceLevelDispatch): __slots__ = "_exec_once_mutex", "_exec_once" def _memoized_attr__exec_once_mutex(self): return threading.Lock() def _exec_once_impl(self, retry_on_exception, *args, **kw): with self._exec_once_mutex: if not self._exec_once: try: self(*args, **kw) exception = False except: exception = True raise finally: if not exception or not retry_on_exception: self._exec_once = True def exec_once(self, *args, **kw): """Execute this event, but only if it has not been executed already for this collection.""" if not self._exec_once: self._exec_once_impl(False, *args, **kw) def exec_once_unless_exception(self, *args, **kw): """Execute this event, but only if it has not been executed already for this collection, or was called by a previous exec_once_unless_exception call and raised an exception. If exec_once was already called, then this method will never run the callable regardless of whether it raised or not. .. versionadded:: 1.3.8 """ if not self._exec_once: self._exec_once_impl(True, *args, **kw) def __call__(self, *args, **kw): """Execute this event.""" for fn in self.parent_listeners: fn(*args, **kw) for fn in self.listeners: fn(*args, **kw) def __len__(self): return len(self.parent_listeners) + len(self.listeners) def __iter__(self): return chain(self.parent_listeners, self.listeners) def __bool__(self): return bool(self.listeners or self.parent_listeners) __nonzero__ = __bool__ class _ListenerCollection(_CompoundListener): """Instance-level attributes on instances of :class:`._Dispatch`. Represents a collection of listeners. As of 0.7.9, _ListenerCollection is only first created via the _EmptyListener.for_modify() method. """ __slots__ = ( "parent_listeners", "parent", "name", "listeners", "propagate", "__weakref__", ) def __init__(self, parent, target_cls): if target_cls not in parent._clslevel: parent.update_subclass(target_cls) self._exec_once = False self.parent_listeners = parent._clslevel[target_cls] self.parent = parent self.name = parent.name self.listeners = collections.deque() self.propagate = set() def for_modify(self, obj): """Return an event collection which can be modified. For _ListenerCollection at the instance level of a dispatcher, this returns self. """ return self def _update(self, other, only_propagate=True): """Populate from the listeners in another :class:`_Dispatch` object.""" existing_listeners = self.listeners existing_listener_set = set(existing_listeners) self.propagate.update(other.propagate) other_listeners = [ l for l in other.listeners if l not in existing_listener_set and not only_propagate or l in self.propagate ] existing_listeners.extend(other_listeners) to_associate = other.propagate.union(other_listeners) registry._stored_in_collection_multi(self, other, to_associate) def insert(self, event_key, propagate): if event_key.prepend_to_list(self, self.listeners): if propagate: self.propagate.add(event_key._listen_fn) def append(self, event_key, propagate): if event_key.append_to_list(self, self.listeners): if propagate: self.propagate.add(event_key._listen_fn) def remove(self, event_key): self.listeners.remove(event_key._listen_fn) self.propagate.discard(event_key._listen_fn) registry._removed_from_collection(event_key, self) def clear(self): registry._clear(self, self.listeners) self.propagate.clear() self.listeners.clear() class _JoinedListener(_CompoundListener): __slots__ = "parent", "name", "local", "parent_listeners" def __init__(self, parent, name, local): self._exec_once = False self.parent = parent self.name = name self.local = local self.parent_listeners = self.local @property def listeners(self): return getattr(self.parent, self.name) def _adjust_fn_spec(self, fn, named): return self.local._adjust_fn_spec(fn, named) def for_modify(self, obj): self.local = self.parent_listeners = self.local.for_modify(obj) return self def insert(self, event_key, propagate): self.local.insert(event_key, propagate) def append(self, event_key, propagate): self.local.append(event_key, propagate) def remove(self, event_key): self.local.remove(event_key) def clear(self): raise NotImplementedError()
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