Struct TtlQueue

pub struct TtlQueue<T> { /* private fields */ }

A queue that drops its content after a given amount of time.

Example

To implement an FPS counter, you could use the following technique:

let mut fps_counter = TtlQueue::new(Duration::from_secs_f64(1.0));

for i in 0..=50 {
    // Register a new frame and return the number of frames observed
    // within the last second.
    let fps = fps_counter.refresh_and_push_back(());
    debug_assert!(fps >= 1);

    // Sleep ~20 ms to achieve a ~50 Hz frequency.
    thread::sleep(Duration::from_millis(19));
}

let fps = fps_counter.refresh();
debug_assert!(fps >= 45 && fps <= 55);

let delta = fps_counter.avg_delta();
debug_assert!(delta >= Duration::from_millis(19) && delta <= Duration::from_millis(21));

Implementations

impl<T> TtlQueue<T>

pub fn new(ttl: Duration) -> Self

Creates an empty TtlQueue with default capacity.

pub fn with_capacity(ttl: Duration, capacity: usize) -> Self

Creates an empty TtlQueue for at least capacity elements.

pub fn push_back(&mut self, element: T)

Pushes an element to the end of the queue.

pub fn refresh_and_push_back(&mut self, element: T) -> usize

Pushes an element to the end of the queue and returns the number of items currently in the queue. This operation is O(N) at worst.

pub fn pop_front(&mut self) -> Option<(Instant, T)>

Gets the element from the front of the queue if it exists, as well as the time instant at which it was added.

pub fn peek_front(&mut self) -> Option<&(Instant, T)>

Similar to pop_front but without removing the element.

pub fn len(&self) -> usize

Gets the number elements currently in the queue, including potentially expired elements.

This operation is O(1). In order to obtain an accurate count in O(N) (worst-case), use refresh instead.

pub fn is_empty(&self) -> bool

Returns true if the queue is definitely empty or false if the queue is possibly empty.

This operation is O(1). In order to obtain an accurate count in O(N) (worst-case), use refresh instead.

pub fn refresh(&mut self) -> usize

Refreshes the queue and returns the number of currently contained elements.

pub fn iter(&self) -> impl Iterator<Item = &(Instant, T)>

Returns an iterator to the data.

pub fn avg_delta(&self) -> Duration

Returns the average duration between two events.

Trait Implementations

impl<T: Debug> Debug for TtlQueue<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> IntoIterator for TtlQueue<T>

type Item = (Instant, T)

The type of the elements being iterated over.

type IntoIter = IntoIter<<TtlQueue<T> as IntoIterator>::Item>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.