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
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
use std::sync::{Arc, Mutex, Weak};
use std::result::Result;
#[derive(Debug)]
pub struct Receiver<T> {
latest: T,
latest_set: Arc<Mutex<Option<T>>>
}
impl<T> Receiver<T> {
fn update_latest(&mut self) {
if let Ok(mut latest_set) = self.latest_set.lock() {
if let Some(value) = latest_set.take() {
self.latest = value;
}
}
}
pub fn latest(&mut self) -> &T {
self.update_latest();
&self.latest
}
pub fn latest_mut(&mut self) -> &mut T {
self.update_latest();
&mut self.latest
}
}
#[derive(Debug, Clone)]
pub struct Updater<T> {
latest: Weak<Mutex<Option<T>>>
}
#[derive(PartialEq, Eq, Clone, Copy, Debug)]
pub struct NoReceiverError<T>(pub T);
impl<T> Updater<T> {
pub fn update(&self, value: T) -> Result<(), NoReceiverError<T>> {
match self.latest.upgrade() {
Some(mutex) => {
*mutex.lock().unwrap() = Some(value);
Ok(())
}
None => Err(NoReceiverError(value))
}
}
pub fn has_no_receiver(&self) -> bool {
self.latest.upgrade().is_none()
}
}
pub fn channel_starting_with<T>(initial: T) -> (Receiver<T>, Updater<T>) {
let receiver = Receiver { latest: initial, latest_set: Arc::new(Mutex::new(None)) };
let updater = Updater { latest: Arc::downgrade(&receiver.latest_set) };
(receiver, updater)
}
pub fn channel<T>() -> (Receiver<Option<T>>, Updater<Option<T>>) {
channel_starting_with(None)
}
#[cfg(test)]
mod test {
use super::*;
use std::{thread, mem};
use std::sync::Barrier;
#[test]
fn send_recv_value() {
let (mut recv, send) = channel_starting_with(12);
assert_eq!(recv.latest(), &12);
send.update(123).unwrap();
assert_eq!(recv.latest(), &123);
}
#[test]
fn send_recv_option() {
let (mut recv, send) = channel_starting_with(None);
assert_eq!(*recv.latest(), None);
send.update(Some(234)).unwrap();
assert_eq!(*recv.latest(), Some(234));
}
fn barrier_pair() -> (Arc<Barrier>, Arc<Barrier>) {
let barrier = Arc::new(Barrier::new(2));
(barrier.clone(), barrier)
}
#[test]
fn concurrent_send_recv() {
let (mut recv, send) = channel_starting_with(0);
let (barrier, barrier2) = barrier_pair();
thread::spawn(move|| {
barrier2.wait();
for num in 1..1000 {
send.update(num).unwrap();
}
send.update(1000).unwrap();
barrier2.wait();
for num in 1001..2001 {
send.update(num).unwrap();
}
barrier2.wait();
});
let mut distinct_recvs = 1;
let mut last_result = *recv.latest();
barrier.wait();
while last_result < 1000 {
let next = *recv.latest();
if next != last_result {
distinct_recvs += 1;
}
last_result = next;
}
assert!(distinct_recvs > 1);
println!("received: {}", distinct_recvs);
assert_eq!(*recv.latest(), 1000);
barrier.wait();
barrier.wait();
assert_eq!(*recv.latest(), 2000);
}
#[test]
fn non_blocking_write_during_read() {
let (mut name_get, name) = channel_starting_with("Nothing".to_owned());
let (barrier, barrier2) = barrier_pair();
thread::spawn(move|| {
barrier2.wait();
name.update("Something".to_owned()).unwrap();
barrier2.wait();
});
{
let got = name_get.latest();
assert_eq!(*got, "Nothing".to_owned());
barrier.wait();
barrier.wait();
}
let got2 = name_get.latest();
assert_eq!(*got2, "Something".to_owned());
}
#[test]
fn error_writing_to_dead_reader() {
let (val_get, val) = channel_starting_with(0);
mem::drop(val_get);
assert_eq!(val.update(123), Err(NoReceiverError(123)));
}
#[test]
fn is_alive() {
let (val_get, val) = channel_starting_with(0);
assert!(!val.has_no_receiver());
mem::drop(val_get);
assert!(val.has_no_receiver());
}
#[test]
fn latest_mut() {
let (mut val_get, _) = channel_starting_with("".to_owned());
{
val_get.latest_mut().push_str("hello");
}
assert_eq!(val_get.latest(), "hello");
}
#[test]
fn multiple_updaters() {
let (mut val_get, val1) = channel_starting_with(0);
let val2 = val1.clone();
val1.update(2).unwrap();
assert_eq!(*val_get.latest(), 2);
val2.update(3).unwrap();
assert_eq!(*val_get.latest(), 3);
}
#[test]
fn no_args_channel() {
let (mut val_get, val) = channel();
assert_eq!(*val_get.latest(), None);
val.update(Some(123)).unwrap();
assert_eq!(*val_get.latest(), Some(123));
}
}