quiche/recovery/
bytes_in_flight.rs

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26
27use std::time::Duration;
28use std::time::Instant;
29
30/// Estimate the total duration a connection has bytes-in-flight.
31///
32/// There can be multiple transitions from bytes-in-flight >0 to 0 and 0 to >0
33/// during a connection's lifetime. Total bytes-in-flight duration is the sum of
34/// all intervals that transition from idle to not-idle and back to idle. Close
35/// intervals are the ones that transitioned back to idle. The open one is the
36/// most recent interval for which we only have a start time, but no end time.
37#[derive(Default)]
38pub struct BytesInFlight {
39    // Current bytes in flight.
40    bytes_in_flight: usize,
41
42    // Instant at which bytes_in_flight transitioned from 0 to >0.
43    // Set if bytes_in_flight is currently >0 which indicates that
44    // the bytes in flight interval is currently "open".
45    bytes_in_flight_interval_start: Option<Instant>,
46
47    // Duration of the current open interval.
48    open_interval_duration: Duration,
49
50    // Sum of closed interval durations seen so far.
51    closed_interval_duration: Duration,
52}
53
54impl BytesInFlight {
55    /// Add to bytes in flight.  Record the start time when
56    /// bytes_in_flight was 0 at the beginning of the function.
57    pub(crate) fn add(&mut self, delta: usize, now: Instant) {
58        if delta == 0 {
59            return;
60        }
61
62        self.bytes_in_flight += delta;
63
64        if self.bytes_in_flight_interval_start.is_some() {
65            self.update_in_flight_duration(now);
66        } else {
67            self.bytes_in_flight_interval_start = Some(now);
68        }
69    }
70
71    /// Substract from bytes in flight.  If bytes_in_flight drops to 0,
72    /// end the current bytes_in_flight >0 interval.
73    pub(crate) fn saturating_subtract(&mut self, delta: usize, now: Instant) {
74        self.bytes_in_flight = self.bytes_in_flight.saturating_sub(delta);
75        self.update_in_flight_duration(now);
76    }
77
78    /// Current bytes in flight.
79    pub(crate) fn get(&self) -> usize {
80        self.bytes_in_flight
81    }
82
83    /// Returns true if there are 0 bytes in flight.
84    pub(crate) fn is_zero(&self) -> bool {
85        self.bytes_in_flight == 0
86    }
87
88    /// Total time during which bytes_in_flight was > 0.
89    pub(crate) fn get_duration(&self) -> Duration {
90        self.closed_interval_duration + self.open_interval_duration
91    }
92
93    fn update_in_flight_duration(&mut self, now: Instant) {
94        if let Some(start) = self.bytes_in_flight_interval_start {
95            if self.bytes_in_flight == 0 {
96                self.open_interval_duration = Duration::ZERO;
97                self.closed_interval_duration += now - start;
98                self.bytes_in_flight_interval_start = None;
99            } else {
100                self.open_interval_duration = now - start;
101            }
102        }
103    }
104}
105
106#[cfg(test)]
107mod tests {
108    use super::*;
109
110    #[test]
111    fn bytes_in_flight_basic() {
112        let start = Instant::now();
113
114        let mut bytes_in_flight: BytesInFlight = Default::default();
115        assert_eq!(bytes_in_flight.get(), 0);
116        assert_eq!(bytes_in_flight.get_duration(), Duration::ZERO);
117
118        // bytes_in_flight_interval_start is initialized when bytes > 0.
119        bytes_in_flight.add(1, start);
120        assert_eq!(bytes_in_flight.get(), 1);
121        assert_eq!(bytes_in_flight.get_duration(), Duration::ZERO);
122
123        // Advance time forward and verify that the inflight time for an open
124        // interval.
125        let mut now = start + Duration::from_secs(2);
126        bytes_in_flight.add(2, now);
127        bytes_in_flight.add(3, now);
128        assert_eq!(bytes_in_flight.get(), 6);
129        // Interval start does not change on adds
130        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(2));
131
132        now += Duration::from_secs(5);
133        bytes_in_flight.saturating_subtract(3, now);
134        // Bytes > 0, interval remains open.
135        assert_eq!(bytes_in_flight.get(), 3);
136        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(7));
137
138        bytes_in_flight.saturating_subtract(3, now);
139        // Bytes == 0, interval is closed.
140        assert_eq!(bytes_in_flight.get(), 0);
141        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(7));
142
143        // Open a second interval.
144        now += Duration::from_secs(30);
145        bytes_in_flight.add(10, now);
146        assert_eq!(bytes_in_flight.get(), 10);
147        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(7));
148
149        // Close the second interval.
150        now += Duration::from_secs(5);
151        bytes_in_flight.saturating_subtract(10, now);
152        assert_eq!(bytes_in_flight.get(), 0);
153        // The two in-flight intervals lasted seven and five seconds, for an
154        // expected total of twelve seconds.
155        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(12));
156    }
157
158    #[test]
159    fn bytes_in_flight_saturating_sub() {
160        let start = Instant::now();
161
162        let mut bytes_in_flight: BytesInFlight = Default::default();
163        bytes_in_flight.add(10, start);
164        assert_eq!(bytes_in_flight.get(), 10);
165
166        bytes_in_flight.saturating_subtract(7, start + Duration::from_secs(3));
167        assert_eq!(bytes_in_flight.get(), 3);
168        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(3));
169        // Interval is still open.
170        bytes_in_flight.saturating_subtract(1, start + Duration::from_secs(20));
171        assert_eq!(bytes_in_flight.get(), 2);
172        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(20));
173
174        bytes_in_flight.saturating_subtract(7, start + Duration::from_secs(25));
175        assert_eq!(bytes_in_flight.get(), 0);
176        // Interval is closed.
177        assert_eq!(bytes_in_flight.get_duration(), Duration::from_secs(25));
178    }
179}
quiche/recovery/bytes_in_flight.rs

quiche/recovery/
bytes_in_flight.rs
