# Copyright 2014-2016 OpenMarket Ltd # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. import logging from typing import ( Any, Awaitable, Callable, Dict, Generic, List, Optional, TypeVar, Union, ) from typing_extensions import ParamSpec from twisted.internet import defer from synapse.logging.context import make_deferred_yieldable, run_in_background from synapse.metrics.background_process_metrics import run_as_background_process from synapse.types import UserID from synapse.util.async_helpers import maybe_awaitable logger = logging.getLogger(__name__) def user_left_room(distributor: "Distributor", user: UserID, room_id: str) -> None: distributor.fire("user_left_room", user=user, room_id=room_id) class Distributor: """A central dispatch point for loosely-connected pieces of code to register, observe, and fire signals. Signals are named simply by strings. TODO(paul): It would be nice to give signals stronger object identities, so we can attach metadata, docstrings, detect typos, etc... But this model will do for today. """ def __init__(self) -> None: self.signals: Dict[str, Signal] = {} self.pre_registration: Dict[str, List[Callable]] = {} def declare(self, name: str) -> None: if name in self.signals: raise KeyError("%r already has a signal named %s" % (self, name)) self.signals[name] = Signal(name) if name in self.pre_registration: signal = self.signals[name] for observer in self.pre_registration[name]: signal.observe(observer) def observe(self, name: str, observer: Callable) -> None: if name in self.signals: self.signals[name].observe(observer) else: # TODO: Avoid strong ordering dependency by allowing people to # pre-register observations on signals that don't exist yet. if name not in self.pre_registration: self.pre_registration[name] = [] self.pre_registration[name].append(observer) def fire(self, name: str, *args: Any, **kwargs: Any) -> None: """Dispatches the given signal to the registered observers. Runs the observers as a background process. Does not return a deferred. """ if name not in self.signals: raise KeyError("%r does not have a signal named %s" % (self, name)) run_as_background_process(name, self.signals[name].fire, *args, **kwargs) P = ParamSpec("P") R = TypeVar("R") class Signal(Generic[P]): """A Signal is a dispatch point that stores a list of callables as observers of it. Signals can be "fired", meaning that every callable observing it is invoked. Firing a signal does not change its state; it can be fired again at any later point. Firing a signal passes any arguments from the fire method into all of the observers. """ def __init__(self, name: str): self.name: str = name self.observers: List[Callable[P, Any]] = [] def observe(self, observer: Callable[P, Any]) -> None: """Adds a new callable to the observer list which will be invoked by the 'fire' method. Each observer callable may return a Deferred.""" self.observers.append(observer) def fire(self, *args: P.args, **kwargs: P.kwargs) -> "defer.Deferred[List[Any]]": """Invokes every callable in the observer list, passing in the args and kwargs. Exceptions thrown by observers are logged but ignored. It is not an error to fire a signal with no observers. Returns a Deferred that will complete when all the observers have completed.""" async def do(observer: Callable[P, Union[R, Awaitable[R]]]) -> Optional[R]: try: return await maybe_awaitable(observer(*args, **kwargs)) except Exception as e: logger.warning( "%s signal observer %s failed: %r", self.name, observer, e, ) return None deferreds = [run_in_background(do, o) for o in self.observers] return make_deferred_yieldable( defer.gatherResults(deferreds, consumeErrors=True) ) def __repr__(self) -> str: return "<Signal name=%r>" % (self.name,)