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use std::prelude::v1::*;
use crate::{
clock, errors::InsufficientCapacity, middleware::RateLimitingMiddleware,
state::keyed::KeyedStateStore, Jitter, NotUntil, RateLimiter,
};
use futures_timer::Delay;
use std::{hash::Hash, num::NonZeroU32};
#[cfg(feature = "std")]
/// # Keyed rate limiters - `async`/`await`
impl<K, S, C, MW> RateLimiter<K, S, C, MW>
where
K: Hash + Eq + Clone,
S: KeyedStateStore<K>,
C: clock::ReasonablyRealtime,
MW: RateLimitingMiddleware<C::Instant, NegativeOutcome = NotUntil<C::Instant>>,
{
/// Asynchronously resolves as soon as the rate limiter allows it.
///
/// When polled, the returned future either resolves immediately (in the case where the rate
/// limiter allows it), or else triggers an asynchronous delay, after which the rate limiter
/// is polled again. This means that the future might resolve at some later time (depending
/// on what other measurements are made on the rate limiter).
///
/// If multiple futures are dispatched against the rate limiter, it is advisable to use
/// [`until_ready_with_jitter`](#method.until_ready_with_jitter), to avoid thundering herds.
pub async fn until_key_ready(&self, key: &K) -> MW::PositiveOutcome {
self.until_key_ready_with_jitter(key, Jitter::NONE).await
}
/// Asynchronously resolves as soon as the rate limiter allows it, with a randomized wait
/// period.
///
/// When polled, the returned future either resolves immediately (in the case where the rate
/// limiter allows it), or else triggers an asynchronous delay, after which the rate limiter
/// is polled again. This means that the future might resolve at some later time (depending
/// on what other measurements are made on the rate limiter).
///
/// This method allows for a randomized additional delay between polls of the rate limiter,
/// which can help reduce the likelihood of thundering herd effects if multiple tasks try to
/// wait on the same rate limiter.
pub async fn until_key_ready_with_jitter(
&self,
key: &K,
jitter: Jitter,
) -> MW::PositiveOutcome {
loop {
match self.check_key(key) {
Ok(x) => {
return x;
}
Err(negative) => {
let delay = Delay::new(jitter + negative.wait_time_from(self.clock.now()));
delay.await;
}
}
}
}
/// Asynchronously resolves as soon as the rate limiter allows it.
///
/// This is similar to `until_key_ready` except it waits for an abitrary number
/// of `n` cells to be available.
///
/// Returns `InsufficientCapacity` if the `n` provided exceeds the maximum
/// capacity of the rate limiter.
pub async fn until_key_n_ready(
&self,
key: &K,
n: NonZeroU32,
) -> Result<MW::PositiveOutcome, InsufficientCapacity> {
self.until_key_n_ready_with_jitter(key, n, Jitter::NONE)
.await
}
/// Asynchronously resolves as soon as the rate limiter allows it, with a
/// randomized wait period.
///
/// This is similar to `until_key_ready_with_jitter` except it waits for an
/// abitrary number of `n` cells to be available.
///
/// Returns `InsufficientCapacity` if the `n` provided exceeds the maximum
/// capacity of the rate limiter.
pub async fn until_key_n_ready_with_jitter(
&self,
key: &K,
n: NonZeroU32,
jitter: Jitter,
) -> Result<MW::PositiveOutcome, InsufficientCapacity> {
loop {
match self.check_key_n(key, n)? {
Ok(x) => {
return Ok(x);
}
Err(negative) => {
let delay = Delay::new(jitter + negative.wait_time_from(self.clock.now()));
delay.await;
}
}
}
}
}