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// This file is part of Substrate.
// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
//! Provides means to implement a typical Pub/Sub mechanism.
//!
//! This module provides a type [`Hub`] which can be used both to subscribe,
//! and to send the broadcast messages.
//!
//! The [`Hub`] type is parametrized by two other types:
//! - `Message` — the type of a message that shall be delivered to the subscribers;
//! - `Registry` — implementation of the subscription/dispatch logic.
//!
//! A Registry is implemented by defining the following traits:
//! - [`Subscribe<K>`];
//! - [`Dispatch<M>`];
//! - [`Unsubscribe`].
//!
//! As a result of subscription `Hub::subscribe` method returns an instance of
//! [`Receiver<Message,Registry>`]. That can be used as a [`Stream`] to receive the messages.
//! Upon drop the [`Receiver<Message, Registry>`] shall unregister itself from the `Hub`.
use std::{
collections::HashMap,
pin::Pin,
sync::{Arc, Weak},
task::{Context, Poll},
};
use futures::stream::{FusedStream, Stream};
// use parking_lot::Mutex;
use parking_lot::ReentrantMutex;
use std::cell::RefCell;
use crate::{
id_sequence::SeqID,
mpsc::{TracingUnboundedReceiver, TracingUnboundedSender},
};
#[cfg(test)]
mod tests;
/// Unsubscribe: unregisters a previously created subscription.
pub trait Unsubscribe {
/// Remove all registrations of the subscriber with ID `subs_id`.
fn unsubscribe(&mut self, subs_id: SeqID);
}
/// Subscribe using a key of type `K`
pub trait Subscribe<K> {
/// Register subscriber with the ID `subs_id` as having interest to the key `K`.
fn subscribe(&mut self, subs_key: K, subs_id: SeqID);
}
/// Dispatch a message of type `M`.
pub trait Dispatch<M> {
/// The type of the that shall be sent through the channel as a result of such dispatch.
type Item;
/// The type returned by the `dispatch`-method.
type Ret;
/// Dispatch the message of type `M`.
///
/// The implementation is given an instance of `M` and is supposed to invoke `dispatch` for
/// each matching subscriber, with an argument of type `Self::Item` matching that subscriber.
///
/// Note that this does not have to be of the same type with the item that will be sent through
/// to the subscribers. The subscribers will receive a message of type `Self::Item`.
fn dispatch<F>(&mut self, message: M, dispatch: F) -> Self::Ret
where
F: FnMut(&SeqID, Self::Item);
}
/// A subscription hub.
///
/// Does the subscription and dispatch.
/// The exact subscription and routing behaviour is to be implemented by the Registry (of type `R`).
/// The Hub under the hood uses the channel defined in `crate::mpsc` module.
#[derive(Debug)]
pub struct Hub<M, R> {
tracing_key: &'static str,
shared: Arc<ReentrantMutex<RefCell<Shared<M, R>>>>,
}
/// The receiving side of the subscription.
///
/// The messages are delivered as items of a [`Stream`].
/// Upon drop this receiver unsubscribes itself from the [`Hub<M, R>`].
#[derive(Debug)]
pub struct Receiver<M, R>
where
R: Unsubscribe,
{
rx: TracingUnboundedReceiver<M>,
shared: Weak<ReentrantMutex<RefCell<Shared<M, R>>>>,
subs_id: SeqID,
}
#[derive(Debug)]
struct Shared<M, R> {
id_sequence: crate::id_sequence::IDSequence,
registry: R,
sinks: HashMap<SeqID, TracingUnboundedSender<M>>,
}
impl<M, R> Hub<M, R>
where
R: Unsubscribe,
{
/// Provide access to the registry (for test purposes).
pub fn map_registry_for_tests<MapF, Ret>(&self, map: MapF) -> Ret
where
MapF: FnOnce(&R) -> Ret,
{
let shared_locked = self.shared.lock();
let shared_borrowed = shared_locked.borrow();
map(&shared_borrowed.registry)
}
}
impl<M, R> Drop for Receiver<M, R>
where
R: Unsubscribe,
{
fn drop(&mut self) {
if let Some(shared) = self.shared.upgrade() {
shared.lock().borrow_mut().unsubscribe(self.subs_id);
}
}
}
impl<M, R> Hub<M, R> {
/// Create a new instance of Hub (with default value for the Registry).
pub fn new(tracing_key: &'static str) -> Self
where
R: Default,
{
Self::new_with_registry(tracing_key, Default::default())
}
/// Create a new instance of Hub over the initialized Registry.
pub fn new_with_registry(tracing_key: &'static str, registry: R) -> Self {
let shared =
Shared { registry, sinks: Default::default(), id_sequence: Default::default() };
let shared = Arc::new(ReentrantMutex::new(RefCell::new(shared)));
Self { tracing_key, shared }
}
/// Subscribe to this Hub using the `subs_key: K`.
///
/// A subscription with a key `K` is possible if the Registry implements `Subscribe<K>`.
pub fn subscribe<K>(&self, subs_key: K, queue_size_warning: usize) -> Receiver<M, R>
where
R: Subscribe<K> + Unsubscribe,
{
let shared_locked = self.shared.lock();
let mut shared_borrowed = shared_locked.borrow_mut();
let subs_id = shared_borrowed.id_sequence.next_id();
// The order (registry.subscribe then sinks.insert) is important here:
// assuming that `Subscribe<K>::subscribe` can panic, it is better to at least
// have the sink disposed.
shared_borrowed.registry.subscribe(subs_key, subs_id);
let (tx, rx) = crate::mpsc::tracing_unbounded(self.tracing_key, queue_size_warning);
assert!(shared_borrowed.sinks.insert(subs_id, tx).is_none(), "Used IDSequence to create another ID. Should be unique until u64 is overflowed. Should be unique.");
Receiver { shared: Arc::downgrade(&self.shared), subs_id, rx }
}
/// Send the message produced with `Trigger`.
///
/// This is possible if the registry implements `Dispatch<Trigger, Item = M>`.
pub fn send<Trigger>(&self, trigger: Trigger) -> <R as Dispatch<Trigger>>::Ret
where
R: Dispatch<Trigger, Item = M>,
{
let shared_locked = self.shared.lock();
let mut shared_borrowed = shared_locked.borrow_mut();
let (registry, sinks) = shared_borrowed.get_mut();
registry.dispatch(trigger, |subs_id, item| {
if let Some(tx) = sinks.get_mut(subs_id) {
if let Err(send_err) = tx.unbounded_send(item) {
log::warn!("Sink with SubsID = {} failed to perform unbounded_send: {} ({} as Dispatch<{}, Item = {}>::dispatch(...))", subs_id, send_err, std::any::type_name::<R>(),
std::any::type_name::<Trigger>(),
std::any::type_name::<M>());
}
} else {
log::warn!(
"No Sink for SubsID = {} ({} as Dispatch<{}, Item = {}>::dispatch(...))",
subs_id,
std::any::type_name::<R>(),
std::any::type_name::<Trigger>(),
std::any::type_name::<M>(),
);
}
})
}
}
impl<M, R> Shared<M, R> {
fn get_mut(&mut self) -> (&mut R, &mut HashMap<SeqID, TracingUnboundedSender<M>>) {
(&mut self.registry, &mut self.sinks)
}
fn unsubscribe(&mut self, subs_id: SeqID)
where
R: Unsubscribe,
{
// The order (sinks.remove then registry.unsubscribe) is important here:
// assuming that `Unsubscribe::unsubscribe` can panic, it is better to at least
// have the sink disposed.
self.sinks.remove(&subs_id);
self.registry.unsubscribe(subs_id);
}
}
impl<M, R> Clone for Hub<M, R> {
fn clone(&self) -> Self {
Self { tracing_key: self.tracing_key, shared: self.shared.clone() }
}
}
impl<M, R> Unpin for Receiver<M, R> where R: Unsubscribe {}
impl<M, R> Stream for Receiver<M, R>
where
R: Unsubscribe,
{
type Item = M;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
Pin::new(&mut self.get_mut().rx).poll_next(cx)
}
}
impl<Ch, R> FusedStream for Receiver<Ch, R>
where
R: Unsubscribe,
{
fn is_terminated(&self) -> bool {
self.rx.is_terminated()
}
}