| // Copyright (C) 2021, Cloudflare, Inc. |
| // All rights reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright notice, |
| // this list of conditions and the following disclaimer. |
| // |
| // * Redistributions in binary form must reproduce the above copyright |
| // notice, this list of conditions and the following disclaimer in the |
| // documentation and/or other materials provided with the distribution. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS |
| // IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, |
| // THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| // PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR |
| // CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
| // EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
| // PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF |
| // LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING |
| // NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS |
| // SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| use std::time::Duration; |
| use std::time::Instant; |
| |
| // When autotuning the receiver window, decide how much |
| // we increase the window. |
| const WINDOW_INCREASE_FACTOR: u64 = 2; |
| |
| // When autotuning the receiver window, check if the last |
| // update is within RTT * this constant. |
| const WINDOW_TRIGGER_FACTOR: u32 = 2; |
| |
| #[derive(Default, Debug)] |
| pub struct FlowControl { |
| /// Total consumed bytes by the receiver. |
| consumed: u64, |
| |
| /// Flow control limit. |
| max_data: u64, |
| |
| /// The receive window. This value is used for updating |
| /// flow control limit. |
| window: u64, |
| |
| /// The maximum receive window. |
| max_window: u64, |
| |
| /// Last update time of max_data for autotuning the window. |
| last_update: Option<Instant>, |
| } |
| |
| impl FlowControl { |
| pub fn new(max_data: u64, window: u64, max_window: u64) -> Self { |
| Self { |
| max_data, |
| |
| window, |
| |
| max_window, |
| |
| ..Default::default() |
| } |
| } |
| |
| /// Returns the current window size. |
| pub fn window(&self) -> u64 { |
| self.window |
| } |
| |
| /// Returns the current flow limit. |
| pub fn max_data(&self) -> u64 { |
| self.max_data |
| } |
| |
| /// Update consumed bytes. |
| pub fn add_consumed(&mut self, consumed: u64) { |
| self.consumed += consumed; |
| } |
| |
| /// Returns true if the flow control needs to update max_data. |
| /// |
| /// This happens when the available window is smaller than the half |
| /// of the current window. |
| pub fn should_update_max_data(&self) -> bool { |
| let available_window = self.max_data - self.consumed; |
| |
| available_window < (self.window / 2) |
| } |
| |
| /// Returns the new max_data limit. |
| pub fn max_data_next(&self) -> u64 { |
| self.consumed + self.window |
| } |
| |
| /// Commits the new max_data limit. |
| pub fn update_max_data(&mut self, now: Instant) { |
| self.max_data = self.max_data_next(); |
| self.last_update = Some(now); |
| } |
| |
| /// Autotune the window size. When there is an another update |
| /// within RTT x 2, bump the window x 1.5, capped by |
| /// max_window. |
| pub fn autotune_window(&mut self, now: Instant, rtt: Duration) { |
| if let Some(last_update) = self.last_update { |
| if now - last_update < rtt * WINDOW_TRIGGER_FACTOR { |
| self.window = std::cmp::min( |
| self.window * WINDOW_INCREASE_FACTOR, |
| self.max_window, |
| ); |
| } |
| } |
| } |
| |
| /// Make sure the lower bound of the window is same to |
| /// the current window. |
| pub fn ensure_window_lower_bound(&mut self, min_window: u64) { |
| if min_window > self.window { |
| self.window = min_window; |
| } |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use super::*; |
| |
| #[test] |
| fn max_data() { |
| let fc = FlowControl::new(100, 20, 100); |
| |
| assert_eq!(fc.max_data(), 100); |
| } |
| |
| #[test] |
| fn should_update_max_data() { |
| let mut fc = FlowControl::new(100, 20, 100); |
| |
| fc.add_consumed(85); |
| assert_eq!(fc.should_update_max_data(), false); |
| |
| fc.add_consumed(10); |
| assert_eq!(fc.should_update_max_data(), true); |
| } |
| |
| #[test] |
| fn max_data_next() { |
| let mut fc = FlowControl::new(100, 20, 100); |
| |
| let consumed = 95; |
| |
| fc.add_consumed(consumed); |
| assert_eq!(fc.should_update_max_data(), true); |
| assert_eq!(fc.max_data_next(), consumed + 20); |
| } |
| |
| #[test] |
| fn update_max_data() { |
| let mut fc = FlowControl::new(100, 20, 100); |
| |
| let consumed = 95; |
| |
| fc.add_consumed(consumed); |
| assert_eq!(fc.should_update_max_data(), true); |
| |
| let max_data_next = fc.max_data_next(); |
| assert_eq!(fc.max_data_next(), consumed + 20); |
| |
| fc.update_max_data(Instant::now()); |
| assert_eq!(fc.max_data(), max_data_next); |
| } |
| |
| #[test] |
| fn autotune_window() { |
| let w = 20; |
| let mut fc = FlowControl::new(100, w, 100); |
| |
| let consumed = 95; |
| |
| fc.add_consumed(consumed); |
| assert_eq!(fc.should_update_max_data(), true); |
| |
| let max_data_next = fc.max_data_next(); |
| assert_eq!(max_data_next, consumed + w); |
| |
| fc.update_max_data(Instant::now()); |
| assert_eq!(fc.max_data(), max_data_next); |
| |
| // Window size should be doubled. |
| fc.autotune_window(Instant::now(), Duration::from_millis(100)); |
| |
| let w = w * 2; |
| let consumed_inc = 15; |
| |
| fc.add_consumed(consumed_inc); |
| assert_eq!(fc.should_update_max_data(), true); |
| |
| let max_data_next = fc.max_data_next(); |
| assert_eq!(max_data_next, consumed + consumed_inc + w); |
| } |
| |
| #[test] |
| fn ensure_window_lower_bound() { |
| let w = 20; |
| let mut fc = FlowControl::new(100, w, 100); |
| |
| // Window doesn't change. |
| fc.ensure_window_lower_bound(w); |
| assert_eq!(fc.window(), 20); |
| |
| // Window changed to the new value. |
| fc.ensure_window_lower_bound(w * 2); |
| assert_eq!(fc.window(), 40); |
| } |
| } |