rate_limit_queue/lib.rs
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#![recursion_limit = "128"]
#[macro_use]
extern crate delegate;
use std::{
collections::VecDeque,
iter::Extend,
thread,
time::{Duration, Instant},
};
#[cfg(test)]
mod tests;
/// A rate limited queue.
pub struct RateLimitQueue<T> {
quantum: usize,
interval: Duration,
queue: VecDeque<T>,
allowance: usize,
timepoint: Instant,
}
/// A type that represents result of `try_dequeue()`.
#[derive(Debug, Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Hash)]
pub enum DequeueResult<T> {
Data(T),
Empty,
Limit(Duration),
}
impl<T> DequeueResult<T> {
pub fn is_data(&self) -> bool {
match self {
DequeueResult::Data(_) => true,
_ => false,
}
}
pub fn is_empty(&self) -> bool {
match self {
DequeueResult::Empty => true,
_ => false,
}
}
pub fn is_limit(&self) -> bool {
match self {
DequeueResult::Limit(_) => true,
_ => false,
}
}
}
impl<T> From<Option<T>> for DequeueResult<T> {
fn from(opt: Option<T>) -> DequeueResult<T> {
opt.map_or(DequeueResult::Empty, DequeueResult::Data)
}
}
impl<T> Into<Option<T>> for DequeueResult<T> {
fn into(self) -> Option<T> {
match self {
DequeueResult::Data(value) => Some(value),
DequeueResult::Empty | DequeueResult::Limit(_) => None,
}
}
}
impl<T> RateLimitQueue<T> {
/// Creates an empty queue.
///
/// # Examples
///
/// ```
/// # use std::time::Duration;
/// use rate_limit_queue::RateLimitQueue;
///
/// let queue: RateLimitQueue<i32> = RateLimitQueue::new(100, Duration::from_secs(1));
/// ```
#[inline]
pub fn new(quantum: usize, interval: Duration) -> RateLimitQueue<T> {
RateLimitQueue::with_capacity(0, quantum, interval)
}
/// Creates an empty queue with space for at least `n` elements.
///
/// # Examples
///
/// ```
/// # use std::time::Duration;
/// use rate_limit_queue::RateLimitQueue;
///
/// let queue: RateLimitQueue<u32> = RateLimitQueue::with_capacity(10, 100, Duration::from_secs(1));
/// ```
#[inline]
pub fn with_capacity(cap: usize, quantum: usize, interval: Duration) -> RateLimitQueue<T> {
RateLimitQueue {
quantum,
interval,
queue: VecDeque::with_capacity(cap),
allowance: quantum,
timepoint: Instant::now(),
}
}
delegate! {
target self.queue {
/// Returns the number of elements the queue can hold without reallocating.
pub fn capacity(&mut self) -> usize;
/// Reserves the minimum capacity for exactly `additional` more elements.
///
/// # Panics
///
/// Panics if the new capacity overflows `usize`.
pub fn reserve_exact(&mut self, additional: usize);
/// Reserves capacity for at least `additional` more elements.
///
/// # Panics
///
/// Panics if the new capacity overflows `usize`.
pub fn reserve(&mut self, additional: usize);
/// Shrinks the capacity of the queue as much as possible.
pub fn shrink_to_fit(&mut self);
/// Shortens the queue, dropping excess elements from the back.
pub fn truncate(&mut self, len: usize);
/// Returns the number of elements in the queue.
pub fn len(&self) -> usize;
/// Returns `true` if the queue is empty.
pub fn is_empty(&self) -> bool;
}
}
/// Changes the quantum.
pub fn set_quantum(&mut self, quantum: usize) {
self.quantum = quantum;
}
/// Changes the interval.
pub fn set_interval(&mut self, interval: Duration) {
self.interval = interval;
}
/// Appends an element to the back of the queue.
///
/// # Examples
///
/// ```
/// # use std::time::Duration;
/// use rate_limit_queue::RateLimitQueue;
///
/// let mut queue = RateLimitQueue::new(100, Duration::from_secs(1));
/// queue.enqueue(1);
/// queue.enqueue(2);
/// ```
pub fn enqueue(&mut self, value: T) {
self.queue.push_back(value);
}
/// Removes the first element and returns it, or `None` if the queue is empty.
///
/// Sleeps if the limit has been reached.
///
/// # Examples
///
/// ```
/// # use std::time::Duration;
/// use rate_limit_queue::RateLimitQueue;
///
/// let mut queue = RateLimitQueue::new(100, Duration::from_secs(1));
/// queue.enqueue(1);
/// queue.enqueue(2);
///
/// assert_eq!(queue.dequeue(), Some(1));
/// assert_eq!(queue.dequeue(), Some(2));
/// ```
pub fn dequeue(&mut self) -> Option<T> {
match self.try_dequeue() {
DequeueResult::Data(value) => Some(value),
DequeueResult::Empty => None,
DequeueResult::Limit(rest) => {
thread::sleep(rest);
if let DequeueResult::Data(value) = self.try_dequeue() {
Some(value)
} else {
unreachable!()
}
}
}
}
/// Tries to remove the first element and return it.
///
/// # Examples
///
/// ```
/// # use std::time::Duration;
/// use rate_limit_queue::{RateLimitQueue, DequeueResult};
///
/// let mut queue = RateLimitQueue::new(2, Duration::from_secs(10));
/// queue.enqueue(1);
/// queue.enqueue(2);
///
/// assert_eq!(queue.try_dequeue(), DequeueResult::Data(1));
/// assert_eq!(queue.try_dequeue(), DequeueResult::Data(2));
/// assert_eq!(queue.try_dequeue(), DequeueResult::Empty);
///
/// queue.enqueue(3);
/// assert!(queue.try_dequeue().is_limit());
/// ```
pub fn try_dequeue(&mut self) -> DequeueResult<T> {
if self.queue.is_empty() {
return DequeueResult::Empty;
}
if self.allowance > 0 {
self.allowance -= 1;
return self.queue.pop_front().into();
}
let now = Instant::now();
let elapsed = now.duration_since(self.timepoint);
match self.interval.checked_sub(elapsed) {
Some(rest) => DequeueResult::Limit(rest),
None => {
self.allowance = self.quantum - 1;
self.timepoint = now;
self.queue.pop_front().into()
}
}
}
/// Returns a front-to-back iterator.
///
/// # Examples
///
/// ```
/// # use std::time::Duration;
/// use rate_limit_queue::{RateLimitQueue, DequeueResult};
///
/// let mut queue = RateLimitQueue::new(2, Duration::from_secs(10));
/// queue.enqueue(1);
/// queue.enqueue(2);
///
/// let b: &[_] = &[&1, &2];
/// let c: Vec<&i32> = queue.iter().collect();
/// assert_eq!(&c[..], b);
/// ```
pub fn iter(&mut self) -> impl Iterator<Item = &T> {
let allowance = &mut self.allowance;
self.queue
.iter()
.take(*allowance)
.inspect(move |_| *allowance -= 1)
}
/// Returns a front-to-back iterator that returns mutable references.
///
/// # Examples
///
/// ```
/// # use std::time::Duration;
/// use rate_limit_queue::{RateLimitQueue, DequeueResult};
///
/// let mut queue = RateLimitQueue::new(2, Duration::from_secs(10));
/// queue.enqueue(1);
/// queue.enqueue(2);
///
/// let b: &[_] = &[&mut 1, &mut 2];
/// let c: Vec<&mut i32> = queue.iter_mut().collect();
/// assert_eq!(&c[..], b);
/// ```
pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut T> {
let allowance = &mut self.allowance;
self.queue
.iter_mut()
.take(*allowance)
.inspect(move |_| *allowance -= 1)
}
}
impl<T> Extend<T> for RateLimitQueue<T> {
fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
self.queue.extend(iter)
}
}