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

// Copyright 2017-2021 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot 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.

// Polkadot 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 Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! Metered variant of unbounded mpsc channels to be able to extract metrics.

use futures::{
	channel::mpsc,
	stream::Stream,
	task::{Context, Poll},
};

use std::{pin::Pin, result};

use super::{measure_tof_check, CoarseInstant, MaybeTimeOfFlight, Meter};

/// Create a wrapped `mpsc::channel` pair of `MeteredSender` and `MeteredReceiver`.
pub fn unbounded<T>() -> (UnboundedMeteredSender<T>, UnboundedMeteredReceiver<T>) {
	let (tx, rx) = mpsc::unbounded::<MaybeTimeOfFlight<T>>();
	let shared_meter = Meter::default();
	let tx = UnboundedMeteredSender { meter: shared_meter.clone(), inner: tx };
	let rx = UnboundedMeteredReceiver { meter: shared_meter, inner: rx };
	(tx, rx)
}

/// A receiver tracking the messages consumed by itself.
#[derive(Debug)]
pub struct UnboundedMeteredReceiver<T> {
	// count currently contained messages
	meter: Meter,
	inner: mpsc::UnboundedReceiver<MaybeTimeOfFlight<T>>,
}

impl<T> std::ops::Deref for UnboundedMeteredReceiver<T> {
	type Target = mpsc::UnboundedReceiver<MaybeTimeOfFlight<T>>;
	fn deref(&self) -> &Self::Target {
		&self.inner
	}
}

impl<T> std::ops::DerefMut for UnboundedMeteredReceiver<T> {
	fn deref_mut(&mut self) -> &mut Self::Target {
		&mut self.inner
	}
}

impl<T> Stream for UnboundedMeteredReceiver<T> {
	type Item = T;
	fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
		match mpsc::UnboundedReceiver::poll_next(Pin::new(&mut self.inner), cx) {
			Poll::Ready(maybe_value) => Poll::Ready(self.maybe_meter_tof(maybe_value)),
			Poll::Pending => Poll::Pending,
		}
	}

	/// Don't rely on the unreliable size hint.
	fn size_hint(&self) -> (usize, Option<usize>) {
		self.inner.size_hint()
	}
}

impl<T> UnboundedMeteredReceiver<T> {
	fn maybe_meter_tof(&mut self, maybe_value: Option<MaybeTimeOfFlight<T>>) -> Option<T> {
		self.meter.note_received();
		maybe_value.map(|value| {
			match value {
				MaybeTimeOfFlight::<T>::WithTimeOfFlight(value, tof_start) => {
					// do not use `.elapsed()` of `std::time`, it may panic
					// `coarsetime` does a saturating substractio for all `CoarseInstant`s
					let duration = tof_start.elapsed();
					self.meter.note_time_of_flight(duration);
					value
				},
				MaybeTimeOfFlight::<T>::Bare(value) => value,
			}
			.into()
		})
	}

	/// Get an updated accessor object for all metrics collected.
	pub fn meter(&self) -> &Meter {
		&self.meter
	}

	/// Attempt to receive the next item.
	pub fn try_next(&mut self) -> Result<Option<T>, mpsc::TryRecvError> {
		match self.inner.try_next()? {
			Some(value) => Ok(self.maybe_meter_tof(Some(value))),
			None => Ok(None),
		}
	}
}

impl<T> futures::stream::FusedStream for UnboundedMeteredReceiver<T> {
	fn is_terminated(&self) -> bool {
		self.inner.is_terminated()
	}
}

/// The sender component, tracking the number of items
/// sent across it.
#[derive(Debug)]
pub struct UnboundedMeteredSender<T> {
	meter: Meter,
	inner: mpsc::UnboundedSender<MaybeTimeOfFlight<T>>,
}

impl<T> Clone for UnboundedMeteredSender<T> {
	fn clone(&self) -> Self {
		Self { meter: self.meter.clone(), inner: self.inner.clone() }
	}
}

impl<T> std::ops::Deref for UnboundedMeteredSender<T> {
	type Target = mpsc::UnboundedSender<MaybeTimeOfFlight<T>>;
	fn deref(&self) -> &Self::Target {
		&self.inner
	}
}

impl<T> std::ops::DerefMut for UnboundedMeteredSender<T> {
	fn deref_mut(&mut self) -> &mut Self::Target {
		&mut self.inner
	}
}

impl<T> UnboundedMeteredSender<T> {
	fn prepare_with_tof(&self, item: T) -> MaybeTimeOfFlight<T> {
		let previous = self.meter.note_sent();
		let item = if measure_tof_check(previous) {
			MaybeTimeOfFlight::WithTimeOfFlight(item, CoarseInstant::now())
		} else {
			MaybeTimeOfFlight::Bare(item)
		};
		item
	}

	/// Get an updated accessor object for all metrics collected.
	pub fn meter(&self) -> &Meter {
		&self.meter
	}

	/// Attempt to send message or fail immediately.
	pub fn unbounded_send(
		&self,
		msg: T,
	) -> result::Result<(), mpsc::TrySendError<MaybeTimeOfFlight<T>>> {
		let msg = self.prepare_with_tof(msg);
		self.inner.unbounded_send(msg).map_err(|e| {
			self.meter.retract_sent();
			e
		})
	}
}