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
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
use std::sync::atomic::AtomicUsize;
use std::sync::atomic::Ordering::Relaxed;
use std::thread::yield_now;
use crate::countedindex::{past, rm_tag};
extern crate parking_lot;
pub const DEFAULT_YIELD_SPINS: usize = 50;
pub const DEFAULT_TRY_SPINS: usize = 50;
pub const DEFAULT_CHECK_DELAY: u64 = 20;
#[inline(always)]
pub fn load_tagless(val: &AtomicUsize) -> usize {
rm_tag(val.load(Relaxed))
}
#[inline(always)]
pub fn check(seq: usize, at: &AtomicUsize, wc: &AtomicUsize) -> bool {
let cur_count = load_tagless(at);
wc.load(Relaxed) == 0 || seq == cur_count || past(seq, cur_count).1
}
pub trait Wait {
fn wait(&self, _: usize, _: &AtomicUsize, _: &AtomicUsize);
fn notify(&self);
fn needs_notify(&self) -> bool;
}
#[derive(Copy, Clone, Default)]
pub struct BusyWait {}
#[derive(Copy, Clone, Default)]
pub struct YieldingWait {
spins_first: usize,
spins_yield: usize,
}
#[derive(Default)]
pub struct BlockingWait {
spins_first: usize,
spins_yield: usize,
lock: parking_lot::Mutex<bool>,
condvar: parking_lot::Condvar,
}
unsafe impl Sync for BusyWait {}
unsafe impl Sync for YieldingWait {}
unsafe impl Sync for BlockingWait {}
unsafe impl Send for BusyWait {}
unsafe impl Send for YieldingWait {}
unsafe impl Send for BlockingWait {}
impl BusyWait {
pub fn new() -> BusyWait {
BusyWait {}
}
}
impl YieldingWait {
pub fn new() -> YieldingWait {
YieldingWait::with_spins(DEFAULT_TRY_SPINS, DEFAULT_YIELD_SPINS)
}
pub fn with_spins(spins_first: usize, spins_yield: usize) -> YieldingWait {
YieldingWait {
spins_first,
spins_yield,
}
}
}
impl BlockingWait {
pub fn new() -> BlockingWait {
BlockingWait::with_spins(DEFAULT_TRY_SPINS, DEFAULT_YIELD_SPINS)
}
pub fn with_spins(spins_first: usize, spins_yield: usize) -> BlockingWait {
BlockingWait {
spins_first,
spins_yield,
lock: parking_lot::Mutex::new(false),
condvar: parking_lot::Condvar::new(),
}
}
}
impl Wait for BusyWait {
#[cold]
fn wait(&self, seq: usize, w_pos: &AtomicUsize, wc: &AtomicUsize) {
loop {
if check(seq, w_pos, wc) {
return;
}
}
}
fn notify(&self) {
}
fn needs_notify(&self) -> bool {
false
}
}
impl Wait for YieldingWait {
#[cold]
fn wait(&self, seq: usize, w_pos: &AtomicUsize, wc: &AtomicUsize) {
for _ in 0..self.spins_first {
if check(seq, w_pos, wc) {
return;
}
}
loop {
yield_now();
for _ in 0..self.spins_yield {
if check(seq, w_pos, wc) {
return;
}
}
}
}
fn notify(&self) {
}
fn needs_notify(&self) -> bool {
false
}
}
impl Wait for BlockingWait {
#[cold]
fn wait(&self, seq: usize, w_pos: &AtomicUsize, wc: &AtomicUsize) {
for _ in 0..self.spins_first {
if check(seq, w_pos, wc) {
return;
}
}
for _ in 0..self.spins_yield {
yield_now();
if check(seq, w_pos, wc) {
return;
}
}
loop {
{
let mut lock = self.lock.lock();
if check(seq, w_pos, wc) {
return;
}
self.condvar.wait(&mut lock);
}
if check(seq, w_pos, wc) {
return;
}
}
}
fn notify(&self) {
let _lock = self.lock.lock();
self.condvar.notify_all();
}
fn needs_notify(&self) -> bool {
true
}
}
impl Clone for BlockingWait {
fn clone(&self) -> BlockingWait {
BlockingWait::with_spins(self.spins_first, self.spins_yield)
}
}
#[cfg(test)]
mod test {
use std::sync::atomic::{fence, AtomicUsize, Ordering};
use std::thread::yield_now;
use super::*;
use crate::broadcast::broadcast_queue_with;
extern crate crossbeam;
use self::crossbeam::scope;
#[inline(never)]
fn waste_some_us(n_us: usize, to: &AtomicUsize) {
for _ in 0..20 * n_us {
to.store(0, Ordering::Relaxed);
fence(Ordering::SeqCst);
}
}
fn mpsc_broadcast<W: Wait + 'static>(senders: usize, receivers: usize, waiter: W) {
let (writer, reader) = broadcast_queue_with(4, waiter);
let num_loop = 1000;
scope(|scope| {
for q in 0..senders {
let cur_writer = writer.clone();
scope.spawn(move |_| {
let v = AtomicUsize::new(0);
'outer: for i in 0..num_loop {
for _ in 0..100000000 {
if cur_writer.try_send((q, i)).is_ok() {
waste_some_us(1, &v);
continue 'outer;
}
yield_now();
}
assert!(false, "Writer could not write");
}
});
}
writer.unsubscribe();
for _ in 0..receivers {
let this_reader = reader.add_stream().into_single().unwrap();
scope.spawn(move |_| {
let mut myv = Vec::new();
for _ in 0..senders {
myv.push(0);
}
for _ in 0..num_loop * senders {
if let Ok(val) = this_reader.recv() {
assert_eq!(myv[val.0], val.1);
myv[val.0] += 1;
} else {
panic!("Writer got disconnected early");
}
}
for val in myv {
if val != num_loop {
panic!("Wrong number of values obtained for this");
}
}
assert!(this_reader.try_recv().is_err());
});
}
reader.unsubscribe();
})
.unwrap();
}
fn test_waiter<T: Wait + Clone + 'static>(waiter: T) {
mpsc_broadcast(2, 2, waiter.clone());
}
#[test]
fn test_busywait() {
test_waiter(BusyWait::new());
}
#[test]
fn test_yieldwait() {
test_waiter(YieldingWait::new());
}
#[test]
fn test_blockingwait() {
test_waiter(BlockingWait::new());
}
#[test]
fn test_blockingwait_nospin() {
test_waiter(BlockingWait::with_spins(0, 0));
}
}