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
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
/// Epoch-based garbage collector.
///
/// # Examples
///
/// ```
/// use crossbeam_epoch::Collector;
///
/// let collector = Collector::new();
///
/// let handle = collector.register();
/// drop(collector); // `handle` still works after dropping `collector`
///
/// handle.pin().flush();
/// ```
use core::fmt;

use crate::guard::Guard;
use crate::internal::{Global, Local};
use crate::primitive::sync::Arc;

/// An epoch-based garbage collector.
pub struct Collector {
    pub(crate) global: Arc<Global>,
}

unsafe impl Send for Collector {}
unsafe impl Sync for Collector {}

impl Default for Collector {
    fn default() -> Self {
        Self {
            global: Arc::new(Global::new()),
        }
    }
}

impl Collector {
    /// Creates a new collector.
    pub fn new() -> Self {
        Self::default()
    }

    /// Registers a new handle for the collector.
    pub fn register(&self) -> LocalHandle {
        Local::register(self)
    }
}

impl Clone for Collector {
    /// Creates another reference to the same garbage collector.
    fn clone(&self) -> Self {
        Collector {
            global: self.global.clone(),
        }
    }
}

impl fmt::Debug for Collector {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.pad("Collector { .. }")
    }
}

impl PartialEq for Collector {
    /// Checks if both handles point to the same collector.
    fn eq(&self, rhs: &Collector) -> bool {
        Arc::ptr_eq(&self.global, &rhs.global)
    }
}
impl Eq for Collector {}

/// A handle to a garbage collector.
pub struct LocalHandle {
    pub(crate) local: *const Local,
}

impl LocalHandle {
    /// Pins the handle.
    #[inline]
    pub fn pin(&self) -> Guard {
        unsafe { (*self.local).pin() }
    }

    /// Returns `true` if the handle is pinned.
    #[inline]
    pub fn is_pinned(&self) -> bool {
        unsafe { (*self.local).is_pinned() }
    }

    /// Returns the `Collector` associated with this handle.
    #[inline]
    pub fn collector(&self) -> &Collector {
        unsafe { (*self.local).collector() }
    }
}

impl Drop for LocalHandle {
    #[inline]
    fn drop(&mut self) {
        unsafe {
            Local::release_handle(&*self.local);
        }
    }
}

impl fmt::Debug for LocalHandle {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.pad("LocalHandle { .. }")
    }
}

#[cfg(all(test, not(crossbeam_loom)))]
mod tests {
    use std::mem;
    use std::sync::atomic::{AtomicUsize, Ordering};

    use crossbeam_utils::thread;

    use crate::{Collector, Owned};

    const NUM_THREADS: usize = 8;

    #[test]
    fn pin_reentrant() {
        let collector = Collector::new();
        let handle = collector.register();
        drop(collector);

        assert!(!handle.is_pinned());
        {
            let _guard = &handle.pin();
            assert!(handle.is_pinned());
            {
                let _guard = &handle.pin();
                assert!(handle.is_pinned());
            }
            assert!(handle.is_pinned());
        }
        assert!(!handle.is_pinned());
    }

    #[test]
    fn flush_local_bag() {
        let collector = Collector::new();
        let handle = collector.register();
        drop(collector);

        for _ in 0..100 {
            let guard = &handle.pin();
            unsafe {
                let a = Owned::new(7).into_shared(guard);
                guard.defer_destroy(a);

                assert!(!(*guard.local).bag.with(|b| (*b).is_empty()));

                while !(*guard.local).bag.with(|b| (*b).is_empty()) {
                    guard.flush();
                }
            }
        }
    }

    #[test]
    fn garbage_buffering() {
        let collector = Collector::new();
        let handle = collector.register();
        drop(collector);

        let guard = &handle.pin();
        unsafe {
            for _ in 0..10 {
                let a = Owned::new(7).into_shared(guard);
                guard.defer_destroy(a);
            }
            assert!(!(*guard.local).bag.with(|b| (*b).is_empty()));
        }
    }

    #[test]
    fn pin_holds_advance() {
        #[cfg(miri)]
        const N: usize = 500;
        #[cfg(not(miri))]
        const N: usize = 500_000;

        let collector = Collector::new();

        thread::scope(|scope| {
            for _ in 0..NUM_THREADS {
                scope.spawn(|_| {
                    let handle = collector.register();
                    for _ in 0..N {
                        let guard = &handle.pin();

                        let before = collector.global.epoch.load(Ordering::Relaxed);
                        collector.global.collect(guard);
                        let after = collector.global.epoch.load(Ordering::Relaxed);

                        assert!(after.wrapping_sub(before) <= 2);
                    }
                });
            }
        })
        .unwrap();
    }

    #[cfg(not(crossbeam_sanitize))] // TODO: assertions failed due to `cfg(crossbeam_sanitize)` reduce `internal::MAX_OBJECTS`
    #[test]
    fn incremental() {
        #[cfg(miri)]
        const COUNT: usize = 500;
        #[cfg(not(miri))]
        const COUNT: usize = 100_000;
        static DESTROYS: AtomicUsize = AtomicUsize::new(0);

        let collector = Collector::new();
        let handle = collector.register();

        unsafe {
            let guard = &handle.pin();
            for _ in 0..COUNT {
                let a = Owned::new(7i32).into_shared(guard);
                guard.defer_unchecked(move || {
                    drop(a.into_owned());
                    DESTROYS.fetch_add(1, Ordering::Relaxed);
                });
            }
            guard.flush();
        }

        let mut last = 0;

        while last < COUNT {
            let curr = DESTROYS.load(Ordering::Relaxed);
            assert!(curr - last <= 1024);
            last = curr;

            let guard = &handle.pin();
            collector.global.collect(guard);
        }
        assert!(DESTROYS.load(Ordering::Relaxed) == COUNT);
    }

    #[test]
    fn buffering() {
        const COUNT: usize = 10;
        #[cfg(miri)]
        const N: usize = 500;
        #[cfg(not(miri))]
        const N: usize = 100_000;
        static DESTROYS: AtomicUsize = AtomicUsize::new(0);

        let collector = Collector::new();
        let handle = collector.register();

        unsafe {
            let guard = &handle.pin();
            for _ in 0..COUNT {
                let a = Owned::new(7i32).into_shared(guard);
                guard.defer_unchecked(move || {
                    drop(a.into_owned());
                    DESTROYS.fetch_add(1, Ordering::Relaxed);
                });
            }
        }

        for _ in 0..N {
            collector.global.collect(&handle.pin());
        }
        assert!(DESTROYS.load(Ordering::Relaxed) < COUNT);

        handle.pin().flush();

        while DESTROYS.load(Ordering::Relaxed) < COUNT {
            let guard = &handle.pin();
            collector.global.collect(guard);
        }
        assert_eq!(DESTROYS.load(Ordering::Relaxed), COUNT);
    }

    #[test]
    fn count_drops() {
        #[cfg(miri)]
        const COUNT: usize = 500;
        #[cfg(not(miri))]
        const COUNT: usize = 100_000;
        static DROPS: AtomicUsize = AtomicUsize::new(0);

        struct Elem(i32);

        impl Drop for Elem {
            fn drop(&mut self) {
                DROPS.fetch_add(1, Ordering::Relaxed);
            }
        }

        let collector = Collector::new();
        let handle = collector.register();

        unsafe {
            let guard = &handle.pin();

            for _ in 0..COUNT {
                let a = Owned::new(Elem(7i32)).into_shared(guard);
                guard.defer_destroy(a);
            }
            guard.flush();
        }

        while DROPS.load(Ordering::Relaxed) < COUNT {
            let guard = &handle.pin();
            collector.global.collect(guard);
        }
        assert_eq!(DROPS.load(Ordering::Relaxed), COUNT);
    }

    #[test]
    fn count_destroy() {
        #[cfg(miri)]
        const COUNT: usize = 500;
        #[cfg(not(miri))]
        const COUNT: usize = 100_000;
        static DESTROYS: AtomicUsize = AtomicUsize::new(0);

        let collector = Collector::new();
        let handle = collector.register();

        unsafe {
            let guard = &handle.pin();

            for _ in 0..COUNT {
                let a = Owned::new(7i32).into_shared(guard);
                guard.defer_unchecked(move || {
                    drop(a.into_owned());
                    DESTROYS.fetch_add(1, Ordering::Relaxed);
                });
            }
            guard.flush();
        }

        while DESTROYS.load(Ordering::Relaxed) < COUNT {
            let guard = &handle.pin();
            collector.global.collect(guard);
        }
        assert_eq!(DESTROYS.load(Ordering::Relaxed), COUNT);
    }

    #[test]
    fn drop_array() {
        const COUNT: usize = 700;
        static DROPS: AtomicUsize = AtomicUsize::new(0);

        struct Elem(i32);

        impl Drop for Elem {
            fn drop(&mut self) {
                DROPS.fetch_add(1, Ordering::Relaxed);
            }
        }

        let collector = Collector::new();
        let handle = collector.register();

        let mut guard = handle.pin();

        let mut v = Vec::with_capacity(COUNT);
        for i in 0..COUNT {
            v.push(Elem(i as i32));
        }

        {
            let a = Owned::new(v).into_shared(&guard);
            unsafe {
                guard.defer_destroy(a);
            }
            guard.flush();
        }

        while DROPS.load(Ordering::Relaxed) < COUNT {
            guard.repin();
            collector.global.collect(&guard);
        }
        assert_eq!(DROPS.load(Ordering::Relaxed), COUNT);
    }

    #[test]
    fn destroy_array() {
        #[cfg(miri)]
        const COUNT: usize = 500;
        #[cfg(not(miri))]
        const COUNT: usize = 100_000;
        static DESTROYS: AtomicUsize = AtomicUsize::new(0);

        let collector = Collector::new();
        let handle = collector.register();

        unsafe {
            let guard = &handle.pin();

            let mut v = Vec::with_capacity(COUNT);
            for i in 0..COUNT {
                v.push(i as i32);
            }

            let ptr = v.as_mut_ptr() as usize;
            let len = v.len();
            guard.defer_unchecked(move || {
                drop(Vec::from_raw_parts(ptr as *const i32 as *mut i32, len, len));
                DESTROYS.fetch_add(len, Ordering::Relaxed);
            });
            guard.flush();

            mem::forget(v);
        }

        while DESTROYS.load(Ordering::Relaxed) < COUNT {
            let guard = &handle.pin();
            collector.global.collect(guard);
        }
        assert_eq!(DESTROYS.load(Ordering::Relaxed), COUNT);
    }

    #[test]
    fn stress() {
        const THREADS: usize = 8;
        #[cfg(miri)]
        const COUNT: usize = 500;
        #[cfg(not(miri))]
        const COUNT: usize = 100_000;
        static DROPS: AtomicUsize = AtomicUsize::new(0);

        struct Elem(i32);

        impl Drop for Elem {
            fn drop(&mut self) {
                DROPS.fetch_add(1, Ordering::Relaxed);
            }
        }

        let collector = Collector::new();

        thread::scope(|scope| {
            for _ in 0..THREADS {
                scope.spawn(|_| {
                    let handle = collector.register();
                    for _ in 0..COUNT {
                        let guard = &handle.pin();
                        unsafe {
                            let a = Owned::new(Elem(7i32)).into_shared(guard);
                            guard.defer_destroy(a);
                        }
                    }
                });
            }
        })
        .unwrap();

        let handle = collector.register();
        while DROPS.load(Ordering::Relaxed) < COUNT * THREADS {
            let guard = &handle.pin();
            collector.global.collect(guard);
        }
        assert_eq!(DROPS.load(Ordering::Relaxed), COUNT * THREADS);
    }
}