sp-utils => sc-utils (#9677)

* sp-utils => sc-utils

* cargo fmt

* These files are now in the client so should be licensed as GPL3

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/utils/src/status_sinks.rs

@@ -0,0 +1,218 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2019-2021 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/>.
+
+use crate::mpsc::{tracing_unbounded, TracingUnboundedReceiver, TracingUnboundedSender};
+use futures::{lock::Mutex, prelude::*};
+use futures_timer::Delay;
+use std::{
+	pin::Pin,
+	task::{Context, Poll},
+	time::Duration,
+};
+
+/// Holds a list of `UnboundedSender`s, each associated with a certain time period. Every time the
+/// period elapses, we push an element on the sender.
+///
+/// Senders are removed only when they are closed.
+pub struct StatusSinks<T> {
+	/// Should only be locked by `next`.
+	inner: Mutex<Inner<T>>,
+	/// Sending side of `Inner::entries_rx`.
+	entries_tx: TracingUnboundedSender<YieldAfter<T>>,
+}
+
+struct Inner<T> {
+	/// The actual entries of the list.
+	entries: stream::FuturesUnordered<YieldAfter<T>>,
+	/// Receives new entries and puts them in `entries`.
+	entries_rx: TracingUnboundedReceiver<YieldAfter<T>>,
+}
+
+struct YieldAfter<T> {
+	delay: Delay,
+	interval: Duration,
+	sender: Option<TracingUnboundedSender<T>>,
+}
+
+impl<T> Default for StatusSinks<T> {
+	fn default() -> Self {
+		Self::new()
+	}
+}
+
+impl<T> StatusSinks<T> {
+	/// Builds a new empty collection.
+	pub fn new() -> StatusSinks<T> {
+		let (entries_tx, entries_rx) = tracing_unbounded("status-sinks-entries");
+
+		StatusSinks {
+			inner: Mutex::new(Inner { entries: stream::FuturesUnordered::new(), entries_rx }),
+			entries_tx,
+		}
+	}
+
+	/// Adds a sender to the collection.
+	///
+	/// The `interval` is the time period between two pushes on the sender.
+	pub fn push(&self, interval: Duration, sender: TracingUnboundedSender<T>) {
+		let _ = self.entries_tx.unbounded_send(YieldAfter {
+			delay: Delay::new(interval),
+			interval,
+			sender: Some(sender),
+		});
+	}
+
+	/// Waits until one of the sinks is ready, then returns an object that can be used to send
+	/// an element on said sink.
+	///
+	/// If the object isn't used to send an element, the slot is skipped.
+	pub async fn next(&self) -> ReadySinkEvent<'_, T> {
+		// This is only ever locked by `next`, which means that one `next` at a time can run.
+		let mut inner = self.inner.lock().await;
+		let inner = &mut *inner;
+
+		loop {
+			// Future that produces the next ready entry in `entries`, or doesn't produce anything
+			// if the list is empty.
+			let next_ready_entry = {
+				let entries = &mut inner.entries;
+				async move {
+					if let Some(v) = entries.next().await {
+						v
+					} else {
+						loop {
+							futures::pending!()
+						}
+					}
+				}
+			};
+
+			futures::select! {
+				new_entry = inner.entries_rx.next() => {
+					if let Some(new_entry) = new_entry {
+						inner.entries.push(new_entry);
+					}
+				},
+				(sender, interval) = next_ready_entry.fuse() => {
+					return ReadySinkEvent {
+						sinks: self,
+						sender: Some(sender),
+						interval,
+					}
+				}
+			}
+		}
+	}
+}
+
+/// One of the sinks is ready.
+#[must_use]
+pub struct ReadySinkEvent<'a, T> {
+	sinks: &'a StatusSinks<T>,
+	sender: Option<TracingUnboundedSender<T>>,
+	interval: Duration,
+}
+
+impl<'a, T> ReadySinkEvent<'a, T> {
+	/// Sends an element on the sender.
+	pub fn send(mut self, element: T) {
+		if let Some(sender) = self.sender.take() {
+			if sender.unbounded_send(element).is_ok() {
+				let _ = self.sinks.entries_tx.unbounded_send(YieldAfter {
+					// Note that since there's a small delay between the moment a task is
+					// woken up and the moment it is polled, the period is actually not
+					// `interval` but `interval + <delay>`. We ignore this problem in
+					// practice.
+					delay: Delay::new(self.interval),
+					interval: self.interval,
+					sender: Some(sender),
+				});
+			}
+		}
+	}
+}
+
+impl<'a, T> Drop for ReadySinkEvent<'a, T> {
+	fn drop(&mut self) {
+		if let Some(sender) = self.sender.take() {
+			if sender.is_closed() {
+				return
+			}
+
+			let _ = self.sinks.entries_tx.unbounded_send(YieldAfter {
+				delay: Delay::new(self.interval),
+				interval: self.interval,
+				sender: Some(sender),
+			});
+		}
+	}
+}
+
+impl<T> futures::Future for YieldAfter<T> {
+	type Output = (TracingUnboundedSender<T>, Duration);
+
+	fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
+		let this = Pin::into_inner(self);
+
+		match Pin::new(&mut this.delay).poll(cx) {
+			Poll::Pending => Poll::Pending,
+			Poll::Ready(()) => {
+				let sender = this
+					.sender
+					.take()
+					.expect("sender is always Some unless the future is finished; qed");
+				Poll::Ready((sender, this.interval))
+			},
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::StatusSinks;
+	use crate::mpsc::tracing_unbounded;
+	use futures::prelude::*;
+	use std::time::Duration;
+
+	#[test]
+	fn works() {
+		// We're not testing that the `StatusSink` properly enforces an order in the intervals, as
+		// this easily causes test failures on busy CPUs.
+
+		let status_sinks = StatusSinks::new();
+
+		let (tx, rx) = tracing_unbounded("test");
+		status_sinks.push(Duration::from_millis(100), tx);
+
+		let mut val_order = 5;
+
+		futures::executor::block_on(futures::future::select(
+			Box::pin(async move {
+				loop {
+					let ev = status_sinks.next().await;
+					val_order += 1;
+					ev.send(val_order);
+				}
+			}),
+			Box::pin(async {
+				let items: Vec<i32> = rx.take(3).collect().await;
+				assert_eq!(items, [6, 7, 8]);
+			}),
+		));
+	}
+}