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use std::time::Duration;
fn randomize(backoff_ms: usize) -> usize {
let new_value = (fastrand::usize(750..=1250) * backoff_ms) / 1000;
if new_value == 0 {
backoff_ms
} else {
new_value
}
}
/// A utility to calculate steps for exponential backoff similar to how it's done in `git`.
pub struct Exponential<Fn> {
multiplier: usize,
max_multiplier: usize,
exponent: usize,
transform: Fn,
}
impl Default for Exponential<fn(usize) -> usize> {
fn default() -> Self {
Exponential {
multiplier: 1,
max_multiplier: 1000,
exponent: 1,
transform: std::convert::identity,
}
}
}
impl Exponential<fn(usize) -> usize> {
/// Create a new exponential backoff iterator that backs off in randomized, ever increasing steps.
pub fn default_with_random() -> Self {
Exponential {
multiplier: 1,
max_multiplier: 1000,
exponent: 1,
transform: randomize,
}
}
}
impl<Transform> Exponential<Transform>
where
Transform: Fn(usize) -> usize,
{
/// Return an iterator that yields `Duration` instances to sleep on until `time` is depleted.
pub fn until_no_remaining(&mut self, time: Duration) -> impl Iterator<Item = Duration> + '_ {
let mut elapsed = Duration::default();
let mut stop_next_iteration = false;
self.take_while(move |d| {
if stop_next_iteration {
false
} else {
elapsed += *d;
if elapsed > time {
stop_next_iteration = true;
}
true
}
})
}
}
impl<Transform> Iterator for Exponential<Transform>
where
Transform: Fn(usize) -> usize,
{
type Item = Duration;
fn next(&mut self) -> Option<Self::Item> {
let wait = Duration::from_millis((self.transform)(self.multiplier) as u64);
self.multiplier += 2 * self.exponent + 1;
if self.multiplier > self.max_multiplier {
self.multiplier = self.max_multiplier;
} else {
self.exponent += 1;
}
Some(wait)
}
}
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