Split the telemetry net status report in two (#3887)

* Split the telemetry net status report in two

* Update core/service/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Remove clone()

* Move code to status_sinks.rs instead

* Add basic usage for status_sinks

* Update core/service/src/status_sinks.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/core/service/src/status_sinks.rs

@@ -0,0 +1,149 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate 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.
+
+// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+use futures::prelude::*;
+use futures::sync::mpsc;
+use futures::stream::futures_unordered::FuturesUnordered;
+use std::time::{Duration, Instant};
+use tokio_timer::Delay;
+
+/// 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> {
+	entries: FuturesUnordered<YieldAfter<T>>,
+}
+
+struct YieldAfter<T> {
+	delay: tokio_timer::Delay,
+	interval: Duration,
+	sender: Option<mpsc::UnboundedSender<T>>,
+}
+
+impl<T> StatusSinks<T> {
+	/// Builds a new empty collection.
+	pub fn new() -> StatusSinks<T> {
+		StatusSinks {
+			entries: FuturesUnordered::new(),
+		}
+	}
+
+	/// Adds a sender to the collection.
+	///
+	/// The `interval` is the time period between two pushes on the sender.
+	pub fn push(&mut self, interval: Duration, sender: mpsc::UnboundedSender<T>) {
+		self.entries.push(YieldAfter {
+			delay: Delay::new(Instant::now() + interval),
+			interval,
+			sender: Some(sender),
+		})
+	}
+
+	/// Processes all the senders. If any sender is ready, calls the `status_grab` function and
+	/// pushes what it returns to the sender.
+	///
+	/// This function doesn't return anything, but it should be treated as if it implicitly
+	/// returns `Ok(Async::NotReady)`. In particular, it should be called again when the task
+	/// is waken up.
+	///
+	/// # Panic
+	///
+	/// Panics if not called within the context of a task.
+	pub fn poll(&mut self, mut status_grab: impl FnMut() -> T) {
+		loop {
+			match self.entries.poll() {
+				Ok(Async::Ready(Some((sender, interval)))) => {
+					let status = status_grab();
+					if sender.unbounded_send(status).is_ok() {
+						self.entries.push(YieldAfter {
+							// Note that since there's a small delay between the moment a task is
+							// waken 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(Instant::now() + interval),
+							interval,
+							sender: Some(sender),
+						});
+					}
+				}
+				Err(()) |
+				Ok(Async::Ready(None)) |
+				Ok(Async::NotReady) => break,
+			}
+		}
+	}
+}
+
+impl<T> Future for YieldAfter<T> {
+	type Item = (mpsc::UnboundedSender<T>, Duration);
+	type Error = ();
+
+	fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+		match self.delay.poll() {
+			Ok(Async::NotReady) => Ok(Async::NotReady),
+			Ok(Async::Ready(())) => {
+				let sender = self.sender.take()
+					.expect("sender is always Some unless the future is finished; qed");
+				Ok(Async::Ready((sender, self.interval)))
+			},
+			Err(_) => Err(()),
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::StatusSinks;
+	use futures::prelude::*;
+	use futures::sync::mpsc;
+	use std::time::Duration;
+
+	#[test]
+	fn basic_usage() {
+		let mut status_sinks = StatusSinks::new();
+
+		let (tx1, rx1) = mpsc::unbounded();
+		status_sinks.push(Duration::from_millis(200), tx1);
+
+		let (tx2, rx2) = mpsc::unbounded();
+		status_sinks.push(Duration::from_millis(500), tx2);
+
+		let mut runtime = tokio::runtime::Runtime::new().unwrap();
+
+		let mut val_order = 5;
+		runtime.spawn(futures::future::poll_fn(move || {
+			status_sinks.poll(|| { val_order += 1; val_order });
+			Ok(Async::NotReady)
+		}));
+
+		let done = rx1
+			.into_future()
+			.and_then(|(item, rest)| {
+				assert_eq!(item, Some(6));
+				rest.into_future()
+			})
+			.and_then(|(item, _)| {
+				assert_eq!(item, Some(7));
+				rx2.into_future()
+			})
+			.map(|(item, _)| {
+				assert_eq!(item, Some(8));
+			});
+
+		runtime.block_on(done).unwrap();
+	}
+}