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
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
//! Loom-based formal verification tests for MPMC queues
//!
//! These tests use the Loom library to exhaustively explore all possible
//! interleavings of concurrent operations to verify correctness under
//! all possible memory ordering scenarios.
#[cfg(test)]
mod loom_tests {
use super::*;
use loom::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
use loom::sync::Arc;
use loom::thread;
use std::sync::Barrier;
/// Simplified bounded queue for Loom testing
///
/// This version uses Loom's atomic types to simulate different
/// memory ordering scenarios and verify correctness.
#[derive(Debug)]
struct LoomBoundedQueue<T> {
buffer: Vec<Option<T>>,
capacity: usize,
mask: usize,
head: AtomicUsize,
tail: AtomicUsize,
}
impl<T> LoomBoundedQueue<T> {
fn new(capacity: usize) -> Self {
let capacity = if capacity.is_power_of_two() {
capacity
} else {
capacity.next_power_of_two()
};
let mask = capacity - 1;
Self {
buffer: (0..capacity).map(|_| None).collect(),
capacity,
mask,
head: AtomicUsize::new(0),
tail: AtomicUsize::new(0),
}
}
fn push(&self, value: T) -> Result<(), ()> {
let tail = self.tail.load(Ordering::Relaxed);
let head = self.head.load(Ordering::Acquire);
// Check if queue is full
if (tail + 1) & self.mask == head {
return Err(());
}
let index = tail & self.mask;
// Check if slot is available
if self.buffer[index].is_some() {
return Err(());
}
// Write the value
self.buffer[index] = Some(value);
// Update tail with Release ordering
self.tail.store(tail + 1, Ordering::Release);
Ok(())
}
fn pop(&self) -> Option<T> {
let head = self.head.load(Ordering::Relaxed);
let tail = self.tail.load(Ordering::Acquire);
// Check if queue is empty
if head == tail {
return None;
}
let index = head & self.mask;
// Try to take the value
if let Some(value) = self.buffer[index].take() {
// Update head with Release ordering
self.head.store(head + 1, Ordering::Release);
Some(value)
} else {
None
}
}
fn len(&self) -> usize {
let head = self.head.load(Ordering::Acquire);
let tail = self.tail.load(Ordering::Acquire);
if tail >= head {
tail - head
} else {
self.capacity - (head - tail)
}
}
fn is_empty(&self) -> bool {
self.len() == 0
}
}
/// Test basic push/pop operations with Loom
#[test]
fn loom_test_basic_operations() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(4));
// Test single producer, single consumer
let queue_clone = Arc::clone(&queue);
let producer = thread::spawn(move || {
queue_clone.push(1).unwrap();
queue_clone.push(2).unwrap();
queue_clone.push(3).unwrap();
});
let consumer = thread::spawn(move || {
thread::yield_now(); // Allow producer to run first
let mut results = Vec::new();
if let Some(value) = queue.pop() {
results.push(value);
}
if let Some(value) = queue.pop() {
results.push(value);
}
if let Some(value) = queue.pop() {
results.push(value);
}
results
});
producer.join().unwrap();
let results = consumer.join().unwrap();
// Verify FIFO ordering
assert_eq!(results, vec![1, 2, 3]);
assert!(queue.is_empty());
});
}
/// Test concurrent producers and consumers
#[test]
fn loom_test_concurrent_producers_consumers() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(8));
let barrier = Arc::new(Barrier::new(3)); // 2 producers + 1 consumer
let queue_clone1 = Arc::clone(&queue);
let barrier_clone1 = Arc::clone(&barrier);
let producer1 = thread::spawn(move || {
barrier_clone1.wait();
queue_clone1.push(1).unwrap();
queue_clone1.push(2).unwrap();
});
let queue_clone2 = Arc::clone(&queue);
let barrier_clone2 = Arc::clone(&barrier);
let producer2 = thread::spawn(move || {
barrier_clone2.wait();
queue_clone2.push(3).unwrap();
queue_clone2.push(4).unwrap();
});
let queue_clone3 = Arc::clone(&queue);
let barrier_clone3 = Arc::clone(&barrier);
let consumer = thread::spawn(move || {
barrier_clone3.wait();
let mut results = Vec::new();
// Try to pop all items
for _ in 0..4 {
if let Some(value) = queue_clone3.pop() {
results.push(value);
}
thread::yield_now();
}
results
});
producer1.join().unwrap();
producer2.join().unwrap();
let results = consumer.join().unwrap();
// Verify all items were received (order may vary due to concurrency)
assert_eq!(results.len(), 4);
assert!(results.contains(&1));
assert!(results.contains(&2));
assert!(results.contains(&3));
assert!(results.contains(&4));
});
}
/// Test queue capacity limits
#[test]
fn loom_test_capacity_limits() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(2));
let queue_clone = Arc::clone(&queue);
let producer = thread::spawn(move || {
// Fill the queue
assert!(queue_clone.push(1).is_ok());
assert!(queue_clone.push(2).is_ok());
// Try to push into full queue
assert!(queue_clone.push(3).is_err());
// Pop one item
assert_eq!(queue_clone.pop(), Some(1));
// Now push should succeed
assert!(queue_clone.push(4).is_ok());
});
producer.join().unwrap();
// Verify final state
assert_eq!(queue.len(), 2);
assert_eq!(queue.pop(), Some(2));
assert_eq!(queue.pop(), Some(4));
assert!(queue.is_empty());
});
}
/// Test memory ordering guarantees
#[test]
fn loom_test_memory_ordering() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(4));
let flag = Arc::new(AtomicUsize::new(0));
let queue_clone1 = Arc::clone(&queue);
let flag_clone1 = Arc::clone(&flag);
let producer = thread::spawn(move || {
// Push a value
queue_clone1.push(42).unwrap();
// Set flag to signal consumer
flag_clone1.store(1, Ordering::Release);
});
let queue_clone2 = Arc::clone(&queue);
let flag_clone2 = Arc::clone(&flag);
let consumer = thread::spawn(move || {
// Wait for flag
while flag_clone2.load(Ordering::Acquire) == 0 {
thread::yield_now();
}
// Should be able to see the pushed value
assert_eq!(queue_clone2.pop(), Some(42));
});
producer.join().unwrap();
consumer.join().unwrap();
assert!(queue.is_empty());
});
}
/// Test ABA problem prevention
#[test]
fn loom_test_aba_prevention() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(4));
// Fill and empty the queue multiple times to test wrap-around
let queue_clone = Arc::clone(&queue);
let thread1 = thread::spawn(move || {
for i in 0..10 {
if queue_clone.push(i).is_ok() {
// Successfully pushed
}
thread::yield_now();
if queue_clone.pop().is_some() {
// Successfully popped
}
thread::yield_now();
}
});
let queue_clone2 = Arc::clone(&queue);
let thread2 = thread::spawn(move || {
for i in 10..20 {
if queue_clone2.push(i).is_ok() {
// Successfully pushed
}
thread::yield_now();
if queue_clone2.pop().is_some() {
// Successfully popped
}
thread::yield_now();
}
});
thread1.join().unwrap();
thread2.join().unwrap();
// Queue should be empty after all operations
// (Note: due to the non-blocking nature, some items might remain)
while queue.pop().is_some() {
// Drain remaining items
}
assert!(queue.is_empty());
});
}
/// Test race conditions in size queries
#[test]
fn loom_test_size_race_conditions() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(8));
let queue_clone1 = Arc::clone(&queue);
let producer = thread::spawn(move || {
for i in 0..4 {
queue_clone1.push(i).unwrap();
thread::yield_now();
}
});
let queue_clone2 = Arc::clone(&queue);
let size_checker = thread::spawn(move || {
let mut sizes = Vec::new();
for _ in 0..8 {
sizes.push(queue_clone2.len());
thread::yield_now();
}
sizes
});
producer.join().unwrap();
let sizes = size_checker.join().unwrap();
// Size should never exceed capacity
for &size in &sizes {
assert!(size <= 8);
}
// Final size should be 4
assert_eq!(queue.len(), 4);
});
}
/// Test error handling under contention
#[test]
fn loom_test_error_handling() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(2));
let errors = Arc::new(AtomicUsize::new(0));
let mut handles = Vec::new();
// Spawn multiple producers trying to push into a small queue
for i in 0..4 {
let queue_clone = Arc::clone(&queue);
let errors_clone = Arc::clone(&errors);
let handle = thread::spawn(move || {
// Try to push multiple items
for j in 0..3 {
if queue_clone.push(i * 10 + j).is_err() {
errors_clone.fetch_add(1, Ordering::Relaxed);
}
thread::yield_now();
}
});
handles.push(handle);
}
// Wait for all producers
for handle in handles {
handle.join().unwrap();
}
// At least some pushes should have failed
let total_errors = errors.load(Ordering::Relaxed);
assert!(total_errors > 0);
// Queue should not be over capacity
assert!(queue.len() <= 2);
});
}
/// Test that all items are eventually consumed
#[test]
fn loom_test_eventual_consumption() {
loom::model(|| {
let queue = Arc::new(LoomBoundedQueue::new(8));
let consumed = Arc::new(AtomicUsize::new(0));
let queue_clone1 = Arc::clone(&queue);
let consumed_clone1 = Arc::clone(&consumed);
let producer = thread::spawn(move || {
for i in 0..6 {
queue_clone1.push(i).unwrap();
thread::yield_now();
}
});
let queue_clone2 = Arc::clone(&queue);
let consumed_clone2 = Arc::clone(&consumed);
let consumer = thread::spawn(move || {
let mut count = 0;
while count < 6 {
if queue_clone2.pop().is_some() {
count += 1;
consumed_clone2.fetch_add(1, Ordering::Relaxed);
}
thread::yield_now();
}
});
producer.join().unwrap();
consumer.join().unwrap();
// All items should have been consumed
assert_eq!(consumed.load(Ordering::Relaxed), 6);
assert!(queue.is_empty());
});
}
}