Make unbounded channels size warning exact (part 1) (paritytech#13490)

* Replace `futures-channel` with `async-channel` in `out_events`

* Apply suggestions from code review

Co-authored-by: Koute <koute@users.noreply.github.com>

* Also print the backtrace of `send()` call

* Switch from `backtrace` crate to `std::backtrace`

* Remove outdated `backtrace` dependency

* Remove `backtrace` from `Cargo.lock`

---------

Co-authored-by: Koute <koute@users.noreply.github.com>

Author: 2 people

Cargo.lock

@@ -15,9 +15,9 @@ targets = ["x86_64-unknown-linux-gnu"]
 
 [dependencies]
 array-bytes = "4.1"
+async-channel = "1.8.0"
 async-trait = "0.1"
 asynchronous-codec = "0.6"
-backtrace = "0.3.67"
 bytes = "1"
 codec = { package = "parity-scale-codec", version = "3.2.2", features = ["derive"] }
 either = "1.5.3"

client/network/Cargo.toml

@@ -31,41 +31,36 @@
 //! - Send events by calling [`OutChannels::send`]. Events are cloned for each sender in the
 //! collection.
 
-use backtrace::Backtrace;
-use futures::{channel::mpsc, prelude::*, ready, stream::FusedStream};
+use futures::{prelude::*, ready, stream::FusedStream};
 use log::error;
 use parking_lot::Mutex;
 use prometheus_endpoint::{register, CounterVec, GaugeVec, Opts, PrometheusError, Registry, U64};
 use sc_network_common::protocol::event::Event;
 use std::{
+	backtrace::Backtrace,
 	cell::RefCell,
 	fmt,
 	pin::Pin,
-	sync::{
-		atomic::{AtomicI64, Ordering},
-		Arc,
-	},
+	sync::Arc,
 	task::{Context, Poll},
 };
 
 /// Creates a new channel that can be associated to a [`OutChannels`].
 ///
 /// The name is used in Prometheus reports, the queue size threshold is used
 /// to warn if there are too many unprocessed events in the channel.
-pub fn channel(name: &'static str, queue_size_warning: i64) -> (Sender, Receiver) {
-	let (tx, rx) = mpsc::unbounded();
+pub fn channel(name: &'static str, queue_size_warning: usize) -> (Sender, Receiver) {
+	let (tx, rx) = async_channel::unbounded();
 	let metrics = Arc::new(Mutex::new(None));
-	let queue_size = Arc::new(AtomicI64::new(0));
 	let tx = Sender {
 		inner: tx,
 		name,
-		queue_size: queue_size.clone(),
 		queue_size_warning,
 		warning_fired: false,
-		creation_backtrace: Backtrace::new_unresolved(),
+		creation_backtrace: Backtrace::force_capture(),
 		metrics: metrics.clone(),
 	};
-	let rx = Receiver { inner: rx, name, queue_size, metrics };
+	let rx = Receiver { inner: rx, name, metrics };
 	(tx, rx)
 }
 
@@ -77,16 +72,11 @@ pub fn channel(name: &'static str, queue_size_warning: i64) -> (Sender, Receiver
 /// implement the `Clone` trait e.g. in Order to not complicate the logic keeping the metrics in
 /// sync on drop. If someone adds a `#[derive(Clone)]` below, it is **wrong**.
 pub struct Sender {
-	inner: mpsc::UnboundedSender<Event>,
+	inner: async_channel::Sender<Event>,
 	/// Name to identify the channel (e.g., in Prometheus and logs).
 	name: &'static str,
-	/// Number of events in the queue. Clone of [`Receiver::in_transit`].
-	// To not bother with ordering and possible underflow errors of the unsigned counter
-	// we just use `i64` and `Ordering::Relaxed`, and perceive `queue_size` as approximate.
-	// It can turn < 0 though.
-	queue_size: Arc<AtomicI64>,
 	/// Threshold queue size to generate an error message in the logs.
-	queue_size_warning: i64,
+	queue_size_warning: usize,
 	/// We generate the error message only once to not spam the logs.
 	warning_fired: bool,
 	/// Backtrace of a place where the channel was created.
@@ -113,9 +103,8 @@ impl Drop for Sender {
 
 /// Receiving side of a channel.
 pub struct Receiver {
-	inner: mpsc::UnboundedReceiver<Event>,
+	inner: async_channel::Receiver<Event>,
 	name: &'static str,
-	queue_size: Arc<AtomicI64>,
 	/// Initially contains `None`, and will be set to a value once the corresponding [`Sender`]
 	/// is assigned to an instance of [`OutChannels`].
 	metrics: Arc<Mutex<Option<Arc<Option<Metrics>>>>>,
@@ -126,7 +115,6 @@ impl Stream for Receiver {
 
 	fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Event>> {
 		if let Some(ev) = ready!(Pin::new(&mut self.inner).poll_next(cx)) {
-			let _ = self.queue_size.fetch_sub(1, Ordering::Relaxed);
 			let metrics = self.metrics.lock().clone();
 			match metrics.as_ref().map(|m| m.as_ref()) {
 				Some(Some(metrics)) => metrics.event_out(&ev, self.name),
@@ -191,17 +179,19 @@ impl OutChannels {
 	/// Sends an event.
 	pub fn send(&mut self, event: Event) {
 		self.event_streams.retain_mut(|sender| {
-			let queue_size = sender.queue_size.fetch_add(1, Ordering::Relaxed);
-			if queue_size == sender.queue_size_warning && !sender.warning_fired {
+			if sender.inner.len() >= sender.queue_size_warning && !sender.warning_fired {
 				sender.warning_fired = true;
-				sender.creation_backtrace.resolve();
 				error!(
-					"The number of unprocessed events in channel `{}` reached {}.\n\
-					 The channel was created at:\n{:?}",
-					sender.name, sender.queue_size_warning, sender.creation_backtrace,
+					"The number of unprocessed events in channel `{}` exceeded {}.\n\
+					 The channel was created at:\n{:}\n
+					 The last event was sent from:\n{:}",
+					sender.name,
+					sender.queue_size_warning,
+					sender.creation_backtrace,
+					Backtrace::force_capture(),
 				);
 			}
-			sender.inner.unbounded_send(event.clone()).is_ok()
+			sender.inner.try_send(event.clone()).is_ok()
 		});
 
 		if let Some(metrics) = &*self.metrics {