path: root/lib/sqlalchemy/event/attr.py

# event/attr.py
# Copyright (C) 2005-2022 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

"""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
from ..util.concurrency import AsyncAdaptedLock


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__ = (
        "clsname",
        "name",
        "arg_names",
        "has_kw",
        "legacy_signatures",
        "_clslevel",
        "__weakref__",
    )

    def __init__(self, parent_dispatch_cls, fn):
        self.name = fn.__name__
        self.clsname = parent_dispatch_cls.__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
            )

        for cls in util.walk_subclasses(target):
            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
            )
        for cls in util.walk_subclasses(target):
            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
        for cls in util.walk_subclasses(target):
            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", "_exec_w_sync_once"

    def _set_asyncio(self):
        self._exec_once_mutex = AsyncAdaptedLock()

    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 _exec_w_sync_on_first_run(self, *args, **kw):
        """Execute this event, and use a mutex if it has not been
        executed already for this collection, or was called
        by a previous _exec_w_sync_on_first_run call and
        raised an exception.

        If _exec_w_sync_on_first_run was already called and didn't raise an
        exception, then a mutex is not used.

        .. versionadded:: 1.4.11

        """
        if not self._exec_w_sync_once:
            with self._exec_once_mutex:
                try:
                    self(*args, **kw)
                except:
                    raise
                else:
                    self._exec_w_sync_once = True
        else:
            self(*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._exec_w_sync_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()