1use slab::Slab;
2
3/// Buffers frames for multiple streams.
4#[derive(Debug)]
5pub struct Buffer<T> {
6 slab: Slab<Slot<T>>,
7}
8
9/// A sequence of frames in a `Buffer`
10#[derive(Debug)]
11pub struct Deque {
12 indices: Option<Indices>,
13}
14
15/// Tracks the head & tail for a sequence of frames in a `Buffer`.
16#[derive(Debug, Default, Copy, Clone)]
17struct Indices {
18 head: usize,
19 tail: usize,
20}
21
22#[derive(Debug)]
23struct Slot<T> {
24 value: T,
25 next: Option<usize>,
26}
27
28impl<T> Buffer<T> {
29 pub fn new() -> Self {
30 Buffer { slab: Slab::new() }
31 }
32
33 pub fn is_empty(&self) -> bool {
34 self.slab.is_empty()
35 }
36}
37
38impl Deque {
39 pub fn new() -> Self {
40 Deque { indices: None }
41 }
42
43 pub fn is_empty(&self) -> bool {
44 self.indices.is_none()
45 }
46
47 pub fn push_back<T>(&mut self, buf: &mut Buffer<T>, value: T) {
48 let key = buf.slab.insert(Slot { value, next: None });
49
50 match self.indices {
51 Some(ref mut idxs) => {
52 buf.slab[idxs.tail].next = Some(key);
53 idxs.tail = key;
54 }
55 None => {
56 self.indices = Some(Indices {
57 head: key,
58 tail: key,
59 });
60 }
61 }
62 }
63
64 pub fn push_front<T>(&mut self, buf: &mut Buffer<T>, value: T) {
65 let key = buf.slab.insert(Slot { value, next: None });
66
67 match self.indices {
68 Some(ref mut idxs) => {
69 buf.slab[key].next = Some(idxs.head);
70 idxs.head = key;
71 }
72 None => {
73 self.indices = Some(Indices {
74 head: key,
75 tail: key,
76 });
77 }
78 }
79 }
80
81 pub fn pop_front<T>(&mut self, buf: &mut Buffer<T>) -> Option<T> {
82 match self.indices {
83 Some(mut idxs) => {
84 let mut slot = buf.slab.remove(idxs.head);
85
86 if idxs.head == idxs.tail {
87 assert!(slot.next.is_none());
88 self.indices = None;
89 } else {
90 idxs.head = slot.next.take().unwrap();
91 self.indices = Some(idxs);
92 }
93
94 Some(slot.value)
95 }
96 None => None,
97 }
98 }
99}
100