1 // Copyright 2022 The ChromiumOS Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 //! Utility file to provide a ratelimit object 6 7 use std::cmp; 8 use std::time::Duration; 9 use std::time::Instant; 10 11 const BUS_LOCK_SLICE_TIME: u32 = 1000000000; 12 13 pub struct Ratelimit { 14 slice_start_time: Instant, 15 slice_end_time: Instant, 16 slice_quota: u64, 17 slice_ns: Duration, 18 dispatched: u64, 19 } 20 21 impl Ratelimit { new() -> Self22 pub fn new() -> Self { 23 Ratelimit { 24 slice_start_time: Instant::now(), 25 slice_end_time: Instant::now(), 26 slice_quota: 0, 27 slice_ns: Duration::new(0, BUS_LOCK_SLICE_TIME), 28 dispatched: 0, 29 } 30 } ratelimit_set_speed(&mut self, speed: u64)31 pub fn ratelimit_set_speed(&mut self, speed: u64) { 32 if speed == 0 { 33 self.slice_quota = 0; 34 } else { 35 self.slice_quota = cmp::max( 36 speed * self.slice_ns.as_nanos() as u64 / BUS_LOCK_SLICE_TIME as u64, 37 1, 38 ); 39 } 40 } 41 /// Calculate and return delay for next request in ns 42 /// Record that we sent n data units (where n matches the scale chosen 43 /// during ratelimit_set_speed).If we may send more data units in the 44 /// current time slice, return 0 (i.e. no delay). 45 /// Otherwise return the amount of time (in ns) until the start of 46 /// the next time slice that will permit sending the next chunk of data. 47 /// 48 /// Recording sent data units even after exceeding the quota is permitted; 49 /// the time slice will be extended accordingly. ratelimit_calculate_delay(&mut self, n: u64) -> u6450 pub fn ratelimit_calculate_delay(&mut self, n: u64) -> u64 { 51 let now: Instant = Instant::now(); 52 if self.slice_quota == 0 { 53 return 0; 54 } 55 if self.slice_end_time < now { 56 // Previous, possibly extended, time slice finished; reset the accounting. 57 self.slice_start_time = now; 58 self.slice_end_time = now + self.slice_ns; 59 self.dispatched = 0; 60 } 61 62 self.dispatched += n; 63 if self.dispatched < self.slice_quota { 64 // We may send further data within the current time slice, 65 // no need to delay the next request. 66 return 0; 67 } 68 // Quota exceeded. Wait based on the excess amount and then start a new slice. 69 let delay_slices: f64 = self.dispatched as f64 / self.slice_quota as f64; 70 self.slice_end_time = self.slice_start_time + delay_slices as u32 * self.slice_ns; 71 (self.slice_end_time - now).as_nanos() as u64 72 } 73 } 74