referrerpolicy=no-referrer-when-downgrade
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
// 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()
	}
}