1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
use std::time::Duration;
use std::iter::Iterator;
use std::u64::MAX as U64_MAX;
#[derive(Debug, Clone)]
pub struct FibonacciBackoff {
curr: u64,
next: u64,
factor: u64,
max_delay: Option<Duration>,
}
impl FibonacciBackoff {
pub fn from_millis(millis: u64) -> FibonacciBackoff {
FibonacciBackoff {
curr: millis,
next: millis,
factor: 1u64,
max_delay: None,
}
}
pub fn factor(mut self, factor: u64) -> FibonacciBackoff {
self.factor = factor;
self
}
pub fn max_delay(mut self, duration: Duration) -> FibonacciBackoff {
self.max_delay = Some(duration);
self
}
}
impl Iterator for FibonacciBackoff {
type Item = Duration;
fn next(&mut self) -> Option<Duration> {
let duration = if let Some(duration) = self.curr.checked_mul(self.factor) {
Duration::from_millis(duration)
} else {
Duration::from_millis(U64_MAX)
};
if let Some(ref max_delay) = self.max_delay {
if duration > *max_delay {
return Some(*max_delay);
}
}
if let Some(next_next) = self.curr.checked_add(self.next) {
self.curr = self.next;
self.next = next_next;
} else {
self.curr = self.next;
self.next = U64_MAX;
}
Some(duration)
}
}
#[test]
fn returns_the_fibonacci_series_starting_at_10() {
let mut iter = FibonacciBackoff::from_millis(10);
assert_eq!(iter.next(), Some(Duration::from_millis(10)));
assert_eq!(iter.next(), Some(Duration::from_millis(10)));
assert_eq!(iter.next(), Some(Duration::from_millis(20)));
assert_eq!(iter.next(), Some(Duration::from_millis(30)));
assert_eq!(iter.next(), Some(Duration::from_millis(50)));
assert_eq!(iter.next(), Some(Duration::from_millis(80)));
}
#[test]
fn saturates_at_maximum_value() {
let mut iter = FibonacciBackoff::from_millis(U64_MAX);
assert_eq!(iter.next(), Some(Duration::from_millis(U64_MAX)));
assert_eq!(iter.next(), Some(Duration::from_millis(U64_MAX)));
}
#[test]
fn stops_increasing_at_max_delay() {
let mut iter = FibonacciBackoff::from_millis(10).max_delay(Duration::from_millis(50));
assert_eq!(iter.next(), Some(Duration::from_millis(10)));
assert_eq!(iter.next(), Some(Duration::from_millis(10)));
assert_eq!(iter.next(), Some(Duration::from_millis(20)));
assert_eq!(iter.next(), Some(Duration::from_millis(30)));
assert_eq!(iter.next(), Some(Duration::from_millis(50)));
assert_eq!(iter.next(), Some(Duration::from_millis(50)));
}
#[test]
fn returns_max_when_max_less_than_base() {
let mut iter = FibonacciBackoff::from_millis(20).max_delay(Duration::from_millis(10));
assert_eq!(iter.next(), Some(Duration::from_millis(10)));
assert_eq!(iter.next(), Some(Duration::from_millis(10)));
}
#[test]
fn can_use_factor_to_get_seconds() {
let factor = 1000;
let mut s = FibonacciBackoff::from_millis(1).factor(factor);
assert_eq!(s.next(), Some(Duration::from_secs(1)));
assert_eq!(s.next(), Some(Duration::from_secs(1)));
assert_eq!(s.next(), Some(Duration::from_secs(2)));
}