Source code for vivarium.framework.event

The Vivarium Event Framework

``vivarium`` constructs and manages the flow of :ref:`time <time_concept>`
through the emission of regularly scheduled events. The tools in this module
manage the relationships between event emitters and listeners and provide
an interface for user :ref:`components <components_concept>` to register
themselves as emitters or listeners to particular events.

The :class:`EventManager` maintains a mapping between event types and channels.
Each event type (and event types must be unique so event type is equivalent to
event name, e.g., ``time_step_prepare``) corresponds to an
:class:`EventChannel`, which tracks listeners to that event in prioritized
levels and passes on the event to those listeners when emitted.

The :class:`EventInterface` is exposed off the :ref:`builder <builder_concept>`
and provides two methods: :func:`get_emitter <EventInterface.get_emitter>`,
which returns a callable emitter for the given event type and
:func:`register_listener <EventInterface.register_listener>`, which adds the
given listener to the event channel for the given event. This is the only part
of the event framework with which client code should interact.

For more information, see the associated event
:ref:`concept note <event_concept>`.

from typing import Any, Callable, Dict, List, NamedTuple, Optional

import pandas as pd

from .lifecycle import ConstraintError
from .time import Time, Timedelta

[docs]class Event(NamedTuple): """An Event object represents the context of an event. Events themselves are just a bundle of data. They must be emitted along an :class:`EventChannel` in order for other simulation components to respond to them. """ #: An index into the population table containing all simulants affected #: by this event. index: pd.Index #: Any additional data provided by the user about the event. user_data: Dict[str, Any] #: The simulation time at which this event will resolve. The current #: simulation size plus the current time step size. time: Time #: The current step size at the time of the event. step_size: Timedelta
[docs] def split(self, new_index: pd.Index) -> "Event": """Create a copy of this event with a new index. This function should be used to emit an event in a new :class:`EventChannel` in response to an event emitted from a different channel. Parameters ---------- new_index An index into the population table containing all simulants affected by this event. Returns ------- Event The new event. """ return Event(new_index, self.user_data, self.time, self.step_size)
def __repr__(self): return ( f"Event(user_data={self.user_data}, time={self.time}, step_size={self.step_size})" ) def __eq__(self, other): return self.__dict__ == other.__dict__
[docs]class EventChannel: """A named subscription channel that passes events to event listeners.""" def __init__(self, manager, name): = f"event_channel_{name}" self.manager = manager self.listeners = [[] for _ in range(10)]
[docs] def emit(self, index: pd.Index, user_data: Dict = None) -> Event: """Notifies all listeners to this channel that an event has occurred. Events are emitted to listeners in order of priority (with order 0 being first and order 9 last), with no ordering within a particular priority level guaranteed. Parameters ---------- index An index into the population table containing all simulants affected by this event. user_data Any additional data provided by the user about the event. """ if not user_data: user_data = {} e = Event( index, user_data, self.manager.clock() + self.manager.step_size(), self.manager.step_size(), ) for priority_bucket in self.listeners: for listener in priority_bucket: listener(e) return e
def __repr__(self): return f"EventChannel(listeners: {[listener for bucket in self.listeners for listener in bucket]})"
[docs]class EventManager: """The configuration for the event system. Notes ----- Client code should never need to interact with this class except through the decorators in this module and the emitter function exposed on the builder during the setup phase. """ def __init__(self): self._event_types = {} @property def name(self): """The name of this component.""" return "event_manager"
[docs] def get_channel(self, name): if name not in self._event_types: self._event_types[name] = EventChannel(self, name) return self._event_types[name]
[docs] def setup(self, builder): """Performs this component's simulation setup. Parameters ---------- builder Object giving access to core framework functionality. """ self.clock = builder.time.clock() self.step_size = builder.time.step_size() builder.event.register_listener("post_setup", self.on_post_setup) self.add_handlers = builder.lifecycle.add_handlers self.add_constraint = builder.lifecycle.add_constraint builder.lifecycle.add_constraint( self.get_emitter, allow_during=["setup", "simulation_end", "report"] ) builder.lifecycle.add_constraint(self.register_listener, allow_during=["setup"])
[docs] def on_post_setup(self, event): for name, channel in self._event_types.items(): self.add_handlers(name, [h for level in channel.listeners for h in level])
[docs] def get_emitter(self, name: str) -> Callable[[pd.Index, Optional[Dict]], Event]: """Get an emitter function for the named event. Parameters ---------- name The name of the event. Returns ------- A function that accepts an index and optional user data. This function creates and timestamps an Event and distributes it to all interested listeners """ channel = self.get_channel(name) try: self.add_constraint(channel.emit, allow_during=[name]) except ConstraintError: # Multiple components have requested this emitter. # Shouldn't happen in production, but happens frequently in tests. pass return channel.emit
[docs] def register_listener(self, name: str, listener: Callable, priority: int = 5): """Registers a new listener to the named event. Parameters ---------- name The name of the event. listener The consumer of the named event. priority Number in range(10) used to assign the ordering in which listeners process the event. """ self.get_channel(name).listeners[priority].append(listener)
[docs] def get_listeners(self, name: str) -> Dict[int, List[Callable]]: """Get all listeners registered for the named event. Parameters ---------- name The name of the event. Returns ------- A dictionary that maps each priority level of the named event's listeners to a list of listeners at that level. """ channel = self.get_channel(name) return { priority: listeners for priority, listeners in enumerate(channel.listeners) if listeners }
[docs] def list_events(self) -> List[Event]: """List all event names known to the event system. Returns ------- List[Event] A list of all known event names. Notes ----- This value can change after setup if components dynamically create new event labels. """ return list(self._event_types.keys())
def __contains__(self, item): return item in self._event_types def __repr__(self): return "EventManager()"
[docs]class EventInterface: """The public interface for the event system.""" def __init__(self, manager: EventManager): self._manager = manager
[docs] def get_emitter(self, name: str) -> Callable[[pd.Index, Optional[Dict]], Event]: """Gets an emitter for a named event. Parameters ---------- name The name of the event the requested emitter will emit. Users may provide their own named events by requesting an emitter with this function, but should do so with caution as it makes time much more difficult to think about. Returns ------- An emitter for the named event. The emitter should be called by the requesting component at the appropriate point in the simulation lifecycle. """ return self._manager.get_emitter(name)
[docs] def register_listener( self, name: str, listener: Callable[[Event], None], priority: int = 5 ) -> None: """Registers a callable as a listener to a events with the given name. The listening callable will be called with a named ``Event`` as its only argument any time the event emitter is invoked from somewhere in the simulation. The framework creates the following events and emits them at different points in the simulation: - At the end of the setup phase: ``post_setup`` - Every time step: - ``time_step__prepare`` - ``time_step`` - ``time_step__cleanup`` - ``collect_metrics`` - At simulation end: ``simulation_end`` Parameters ---------- name The name of the event to listen for. listener The callable to be invoked any time an :class:`Event` with the given name is emitted. priority One of {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}. An indication of the order in which event listeners should be called. Listeners with smaller priority values will be called earlier. Listeners with the same priority have no guaranteed ordering. This feature should be avoided if possible. Components should strive to obey the Markov property as they transform the state table (the state of the simulation at the beginning of the next time step should only depend on the current state of the system). """ self._manager.register_listener(name, listener, priority)