async_rate_limit/sliding_window.rs
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use std::sync::Arc;
use crate::limiters::{ThreadsafeRateLimiter, ThreadsafeVariableRateLimiter};
use tokio::sync::{OwnedSemaphorePermit, Semaphore};
use tokio::time::Duration;
/// A rate limiter that records calls (optionally with a specified cost) during a sliding window `Duration`.
///
/// [`SlidingWindowRateLimiter`] implements both [`RateLimiter`] and [`VariableCostRateLimiter`], so both
/// [`SlidingWindowRateLimiter::wait_until_ready()`] and [`SlidingWindowRateLimiter::wait_with_cost()`] can be used (even together). For instance, `limiter.wait_until_ready().await`
/// and `limiter.wait_with_cost(1).await` would have the same effect.
///
/// # Example: Simple Rate Limiter
///
/// A method that calls an external API with a rate limit should not be called more than three times per second.
/// ```
/// use tokio::time::{Instant, Duration};
/// use async_rate_limit::limiters::RateLimiter;
/// use async_rate_limit::sliding_window::SlidingWindowRateLimiter;
///
/// #[tokio::main]
/// async fn main() -> () {
/// let mut limiter = SlidingWindowRateLimiter::new(Duration::from_secs(1), 3);
///
/// for _ in 0..4 {
/// // the 4th call will take place ~1 second after the first call
/// limited_method(&mut limiter).await;
/// }
/// }
///
/// // note the use of the `RateLimiter` trait, rather than the direct type
/// async fn limited_method<T>(limiter: &mut T) where T: RateLimiter {
/// limiter.wait_until_ready().await;
/// println!("{:?}", Instant::now());
/// }
/// ```
///
#[derive(Clone, Debug)]
pub struct SlidingWindowRateLimiter {
/// Length of the window, i.e. a permit acquired at T is released at T + window
window: Duration,
/// Number of calls (or cost thereof) allowed during a given sliding window
permits: Arc<Semaphore>,
}
impl SlidingWindowRateLimiter {
/// Creates a new `SlidingWindowRateLimiter` that allows `limit` calls during any `window` Duration.
pub fn new(window: Duration, limit: usize) -> Self {
let permits = Arc::new(Semaphore::new(limit));
SlidingWindowRateLimiter { window, permits }
}
/// Creates a new `SlidingWindowRateLimiter` with an externally provided `Arc<Semaphore>` for permits.
/// # Example: A Shared Variable Cost Rate Limiter
///
/// ```
/// use std::sync::Arc;
/// use tokio::sync::Semaphore;
/// use async_rate_limit::limiters::VariableCostRateLimiter;
/// use async_rate_limit::sliding_window::SlidingWindowRateLimiter;
/// use tokio::time::{Instant, Duration};
///
/// #[tokio::main]
/// async fn main() -> () {
/// let permits = Arc::new(Semaphore::new(5));
/// let mut limiter1 =
/// SlidingWindowRateLimiter::new_with_permits(Duration::from_secs(2), permits.clone());
/// let mut limiter2 =
/// SlidingWindowRateLimiter::new_with_permits(Duration::from_secs(2), permits.clone());
///
/// // Note: the above is semantically equivalent to creating `limiter1` with
/// // `SlidingWindowRateLimiter::new`, then cloning it.
///
/// limiter1.wait_with_cost(3).await;
/// // the second call will wait 2s, since the first call consumed 3/5 shared permits
/// limiter2.wait_with_cost(3).await;
/// }
/// ```
pub fn new_with_permits(window: Duration, permits: Arc<Semaphore>) -> Self {
SlidingWindowRateLimiter { window, permits }
}
async fn drop_permit_after_window(window: Duration, permit: OwnedSemaphorePermit) {
tokio::time::sleep(window).await;
drop(permit);
}
}
impl ThreadsafeRateLimiter for SlidingWindowRateLimiter {
/// Wait with an implied cost of 1, see the [initial example](#example-simple-rate-limiter)
async fn wait_until_ready(&self) {
let permit = self
.permits
.clone()
.acquire_owned()
.await
.expect("Failed to acquire permit for call");
tokio::spawn(Self::drop_permit_after_window(self.window, permit));
}
}
impl ThreadsafeVariableRateLimiter for SlidingWindowRateLimiter {
/// Wait with some variable cost per usage.
///
/// # Example: A Shared Variable Cost Rate Limiter
///
/// An API specifies that you may make 5 "calls" per second, but some endpoints cost more than one call.
/// - `/lite` costs 1 unit per call
/// - `/heavy` costs 3 units per call
/// ```
/// use tokio::time::{Instant, Duration};
/// use async_rate_limit::limiters::VariableCostRateLimiter;
/// use async_rate_limit::sliding_window::SlidingWindowRateLimiter;
///
/// #[tokio::main]
/// async fn main() -> () {
/// let mut limiter = SlidingWindowRateLimiter::new(Duration::from_secs(1), 5);
///
/// for _ in 0..3 {
/// // these will proceed immediately, spending 3 units
/// get_lite(&mut limiter).await;
/// }
///
/// // 3/5 units are spent, so this will wait for ~1s to proceed since it costs another 3
/// get_heavy(&mut limiter).await;
/// }
///
/// // note the use of the `VariableCostRateLimiter` trait, rather than the direct type
/// async fn get_lite<T>(limiter: &mut T) where T: VariableCostRateLimiter {
/// limiter.wait_with_cost(1).await;
/// println!("Lite: {:?}", Instant::now());
/// }
///
/// async fn get_heavy<T>(limiter: &mut T) where T: VariableCostRateLimiter {
/// limiter.wait_with_cost(3).await;
/// println!("Heavy: {:?}", Instant::now());
/// }
/// ```
async fn wait_with_cost(&self, cost: usize) {
let permits = self
.permits
.clone()
.acquire_many_owned(cost as u32)
.await
.unwrap_or_else(|_| panic!("Failed to acquire {} permits for call", cost));
tokio::spawn(Self::drop_permit_after_window(self.window, permits));
}
}
#[cfg(test)]
mod tests {
use super::*;
use tokio::time::{pause, Instant};
mod rate_limiter_tests {
use super::*;
use crate::limiters::{RateLimiter, ThreadsafeRateLimiter};
#[tokio::test]
async fn test_proceeds_immediately_below_limit() {
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(3), 7);
let start = Instant::now();
for _ in 0..7 {
limiter.wait_until_ready().await;
}
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(0));
assert!(duration < Duration::from_millis(100));
}
#[tokio::test]
async fn test_waits_at_limit() {
pause();
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(1), 3);
let start = Instant::now();
for _ in 0..10 {
limiter.wait_until_ready().await;
}
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(3));
assert!(duration < Duration::from_secs(4));
}
#[tokio::test]
async fn test_many_simultaneous_waiters() {
pause();
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(1), 3);
let start = Instant::now();
let mut tasks = vec![];
for _ in 0..10 {
let limiter_clone = Arc::new(tokio::sync::Mutex::new(limiter.clone()));
let task = tokio::spawn(async move {
let limiter = limiter_clone.lock().await;
(*limiter).wait_until_ready().await;
});
tasks.push(task);
}
for task in tasks.into_iter() {
let _ = task.await;
}
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(3));
assert!(duration < Duration::from_secs(4));
}
#[tokio::test]
async fn test_trait_threadsafe_bounds() {
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(3), 7);
assert_threadsafe(&limiter).await;
}
#[tokio::test]
async fn test_trait_non_threadsafe_bounds() {
let mut limiter = SlidingWindowRateLimiter::new(Duration::from_secs(3), 7);
assert_non_threadsafe(&mut limiter).await;
}
async fn assert_threadsafe<T: ThreadsafeRateLimiter>(limiter: &T) {
let start = Instant::now();
for _ in 0..7 {
limiter.wait_until_ready().await;
}
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(0));
assert!(duration < Duration::from_millis(100));
}
async fn assert_non_threadsafe<T: RateLimiter>(limiter: &mut T) {
let start = Instant::now();
for _ in 0..7 {
limiter.wait_until_ready().await;
}
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(0));
assert!(duration < Duration::from_millis(100));
}
}
mod variable_cost_rate_limiter_tests {
use super::*;
use crate::limiters::ThreadsafeVariableRateLimiter;
#[tokio::test]
async fn test_proceeds_immediately_below_limit() {
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(3), 7);
let start = Instant::now();
for _ in 0..3 {
limiter.wait_with_cost(2).await;
}
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(0));
assert!(duration < Duration::from_millis(100));
}
#[tokio::test]
async fn test_waits_at_limit() {
pause();
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(1), 3);
let start = Instant::now();
limiter.wait_with_cost(3).await;
limiter.wait_with_cost(3).await;
limiter.wait_with_cost(3).await;
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(2));
assert!(duration < Duration::from_secs(3));
}
#[tokio::test]
async fn test_with_threadsafe_bound() {
pause();
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(1), 3);
assert_threadsafe(&limiter).await;
}
async fn assert_threadsafe<T>(limiter: &T)
where
T: ThreadsafeVariableRateLimiter,
{
let start = Instant::now();
limiter.wait_with_cost(3).await;
limiter.wait_with_cost(3).await;
limiter.wait_with_cost(3).await;
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(2));
assert!(duration < Duration::from_secs(3));
}
#[tokio::test]
async fn test_waiters_with_shared_permits() {
pause();
let permits = Arc::new(Semaphore::new(5));
let limiter1 =
SlidingWindowRateLimiter::new_with_permits(Duration::from_secs(2), permits.clone());
let limiter2 =
SlidingWindowRateLimiter::new_with_permits(Duration::from_secs(2), permits.clone());
let start = Instant::now();
limiter1.wait_with_cost(3).await;
limiter2.wait_with_cost(3).await;
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(2));
assert!(duration < Duration::from_secs(3));
}
#[tokio::test]
async fn test_many_waiters() {
pause();
let limiter = SlidingWindowRateLimiter::new(Duration::from_secs(1), 3);
let start = Instant::now();
let mut tasks = vec![];
for _ in 0..10 {
let limiter_clone = Arc::new(tokio::sync::Mutex::new(limiter.clone()));
let task = tokio::spawn(async move {
let limiter = limiter_clone.lock().await;
(*limiter).wait_with_cost(3).await;
});
tasks.push(task);
}
for task in tasks.into_iter() {
let _ = task.await;
}
let end = Instant::now();
let duration = end - start;
assert!(duration > Duration::from_secs(9));
assert!(duration < Duration::from_secs(10));
}
}
}