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
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
//! # Flume
//!
//! A blazingly fast multi-producer, multi-consumer channel.
//!
//! *"Do not communicate by sharing memory; instead, share memory by communicating."*
//!
//! ## Why Flume?
//!
//! - **Featureful**: Unbounded, bounded and rendezvous queues
//! - **Fast**: Always faster than `std::sync::mpsc` and sometimes `crossbeam-channel`
//! - **Safe**: No `unsafe` code anywhere in the codebase!
//! - **Flexible**: `Sender` and `Receiver` both implement `Send + Sync + Clone`
//! - **Familiar**: Drop-in replacement for `std::sync::mpsc`
//! - **Capable**: Additional features like MPMC support and send timeouts/deadlines
//! - **Simple**: Few dependencies, minimal codebase, fast to compile
//! - **Asynchronous**: `async` support, including mix 'n match with sync code
//! - **Ergonomic**: Powerful `select`-like interface
//!
//! ## Example
//!
//! ```
//! let (tx, rx) = flume::unbounded();
//!
//! tx.send(42).unwrap();
//! assert_eq!(rx.recv().unwrap(), 42);
//! ```

#![deny(missing_docs)]

#[cfg(feature = "select")]
pub mod select;
#[cfg(feature = "async")]
pub mod r#async;

mod signal;

// Reexports
#[cfg(feature = "select")]
pub use select::Selector;

use std::{
    collections::VecDeque,
    sync::{Arc, atomic::{AtomicUsize, AtomicBool, Ordering}},
    time::{Duration, Instant},
    marker::PhantomData,
    thread,
    fmt,
};

use spin1::{Mutex as Spinlock, MutexGuard as SpinlockGuard};
use crate::signal::{Signal, SyncSignal};

/// An error that may be emitted when attempting to send a value into a channel on a sender when
/// all receivers are dropped.
#[derive(Copy, Clone, PartialEq, Eq)]
pub struct SendError<T>(pub T);

impl<T> SendError<T> {
    /// Consume the error, yielding the message that failed to send.
    pub fn into_inner(self) -> T { self.0 }
}

impl<T> fmt::Debug for SendError<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        "SendError(..)".fmt(f)
    }
}

impl<T> fmt::Display for SendError<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        "sending on a closed channel".fmt(f)
    }
}

impl<T> std::error::Error for SendError<T> {}

/// An error that may be emitted when attempting to send a value into a channel on a sender when
/// the channel is full or all receivers are dropped.
#[derive(Copy, Clone, PartialEq, Eq)]
pub enum TrySendError<T> {
    /// The channel the message is sent on has a finite capacity and was full when the send was attempted.
    Full(T),
    /// All channel receivers were dropped and so the message has nobody to receive it.
    Disconnected(T),
}

impl<T> TrySendError<T> {
    /// Consume the error, yielding the message that failed to send.
    pub fn into_inner(self) -> T {
        match self {
            Self::Full(msg) | Self::Disconnected(msg) => msg,
        }
    }
}

impl<T> fmt::Debug for TrySendError<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            TrySendError::Full(..) => "Full(..)".fmt(f),
            TrySendError::Disconnected(..) => "Disconnected(..)".fmt(f),
        }
    }
}

impl<T> fmt::Display for TrySendError<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            TrySendError::Full(..) => "sending on a full channel".fmt(f),
            TrySendError::Disconnected(..) => "sending on a closed channel".fmt(f),
        }
    }
}

impl<T> std::error::Error for TrySendError<T> {}

impl<T> From<SendError<T>> for TrySendError<T> {
    fn from(err: SendError<T>) -> Self {
        match err {
            SendError(item) => Self::Disconnected(item),
        }
    }
}

/// An error that may be emitted when sending a value into a channel on a sender with a timeout when
/// the send operation times out or all receivers are dropped.
#[derive(Copy, Clone, PartialEq, Eq)]
pub enum SendTimeoutError<T> {
    /// A timeout occurred when attempting to send the message.
    Timeout(T),
    /// All channel receivers were dropped and so the message has nobody to receive it.
    Disconnected(T),
}

impl<T> SendTimeoutError<T> {
    /// Consume the error, yielding the message that failed to send.
    pub fn into_inner(self) -> T {
        match self {
            Self::Timeout(msg) | Self::Disconnected(msg) => msg,
        }
    }
}

impl<T> fmt::Debug for SendTimeoutError<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        "SendTimeoutError(..)".fmt(f)
    }
}

impl<T> fmt::Display for SendTimeoutError<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            SendTimeoutError::Timeout(..) => "timed out sending on a full channel".fmt(f),
            SendTimeoutError::Disconnected(..) => "sending on a closed channel".fmt(f),
        }
    }
}

impl<T> std::error::Error for SendTimeoutError<T> {}

impl<T> From<SendError<T>> for SendTimeoutError<T> {
    fn from(err: SendError<T>) -> Self {
        match err {
            SendError(item) => Self::Disconnected(item),
        }
    }
}

enum TrySendTimeoutError<T> {
    Full(T),
    Disconnected(T),
    Timeout(T),
}

/// An error that may be emitted when attempting to wait for a value on a receiver when all senders
/// are dropped and there are no more messages in the channel.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum RecvError {
    /// All senders were dropped and no messages are waiting in the channel, so no further messages can be received.
    Disconnected,
}

impl fmt::Display for RecvError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            RecvError::Disconnected => "receiving on a closed channel".fmt(f),
        }
    }
}

impl std::error::Error for RecvError {}

/// An error that may be emitted when attempting to fetch a value on a receiver when there are no
/// messages in the channel. If there are no messages in the channel and all senders are dropped,
/// then `TryRecvError::Disconnected` will be returned.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum TryRecvError {
    /// The channel was empty when the receive was attempted.
    Empty,
    /// All senders were dropped and no messages are waiting in the channel, so no further messages can be received.
    Disconnected,
}

impl fmt::Display for TryRecvError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            TryRecvError::Empty => "receiving on an empty channel".fmt(f),
            TryRecvError::Disconnected => "channel is empty and closed".fmt(f),
        }
    }
}

impl std::error::Error for TryRecvError {}

impl From<RecvError> for TryRecvError {
    fn from(err: RecvError) -> Self {
        match err {
            RecvError::Disconnected => Self::Disconnected,
        }
    }
}

/// An error that may be emitted when attempting to wait for a value on a receiver with a timeout
/// when the receive operation times out or all senders are dropped and there are no values left
/// in the channel.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum RecvTimeoutError {
    /// A timeout occurred when attempting to receive a message.
    Timeout,
    /// All senders were dropped and no messages are waiting in the channel, so no further messages can be received.
    Disconnected,
}

impl fmt::Display for RecvTimeoutError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            RecvTimeoutError::Timeout => "timed out waiting on a channel".fmt(f),
            RecvTimeoutError::Disconnected => "channel is empty and closed".fmt(f),
        }
    }
}

impl std::error::Error for RecvTimeoutError {}

impl From<RecvError> for RecvTimeoutError {
    fn from(err: RecvError) -> Self {
        match err {
            RecvError::Disconnected => Self::Disconnected,
        }
    }
}

enum TryRecvTimeoutError {
    Empty,
    Timeout,
    Disconnected,
}

// TODO: Investigate some sort of invalidation flag for timeouts
struct Hook<T, S: ?Sized>(Option<Spinlock<Option<T>>>, S);

impl<T, S: ?Sized + Signal> Hook<T, S> {
    pub fn slot(msg: Option<T>, signal: S) -> Arc<Self> where S: Sized {
        Arc::new(Self(Some(Spinlock::new(msg)), signal))
    }

    pub fn trigger(signal: S) -> Arc<Self> where S: Sized {
        Arc::new(Self(None, signal))
    }

    pub fn signal(&self) -> &S {
        &self.1
    }

    pub fn fire_nothing(&self) -> bool {
        self.signal().fire()
    }

    pub fn fire_recv(&self) -> (T, &S) {
        let msg = self.0.as_ref().unwrap().lock().take().unwrap();
        (msg, self.signal())
    }

    pub fn fire_send(&self, msg: T) -> (Option<T>, &S) {
        let ret = match &self.0 {
            Some(hook) => {
                *hook.lock() = Some(msg);
                None
            },
            None => Some(msg),
        };
        (ret, self.signal())
    }

    pub fn is_empty(&self) -> bool {
        self.0.as_ref().map(|s| s.lock().is_none()).unwrap_or(true)
    }

    pub fn try_take(&self) -> Option<T> {
        self.0.as_ref().and_then(|s| s.lock().take())
    }
}

impl<T> Hook<T, SyncSignal> {
    pub fn wait_recv(&self, abort: &AtomicBool) -> Option<T> {
        loop {
            let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
            let msg = self.0.as_ref().unwrap().lock().take();
            if let Some(msg) = msg {
                break Some(msg);
            } else if disconnected {
                break None;
            } else {
                self.signal().wait()
            }
        }
    }

    // Err(true) if timeout
    pub fn wait_deadline_recv(&self, abort: &AtomicBool, deadline: Instant) -> Result<T, bool> {
        loop {
            let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
            let msg = self.0.as_ref().unwrap().lock().take();
            if let Some(msg) = msg {
                break Ok(msg);
            } else if disconnected {
                break Err(false);
            } else if let Some(dur) = deadline.checked_duration_since(Instant::now()) {
                self.signal().wait_timeout(dur);
            } else {
                break Err(true);
            }
        }
    }

    pub fn wait_send(&self, abort: &AtomicBool) {
        loop {
            let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
            if disconnected || self.0.as_ref().unwrap().lock().is_none() {
                break;
            }

            self.signal().wait();
        }
    }

    // Err(true) if timeout
    pub fn wait_deadline_send(&self, abort: &AtomicBool, deadline: Instant) -> Result<(), bool> {
        loop {
            let disconnected = abort.load(Ordering::SeqCst); // Check disconnect *before* msg
            if self.0.as_ref().unwrap().lock().is_none() {
                break Ok(());
            } else if disconnected {
                break Err(false);
            } else if let Some(dur) = deadline.checked_duration_since(Instant::now()) {
                self.signal().wait_timeout(dur);
            } else {
                break Err(true);
            }
        }
    }
}

#[cfg(feature = "spin")]
#[inline]
fn wait_lock<T>(lock: &Spinlock<T>) -> SpinlockGuard<T> {
    let mut i = 4;
    loop {
        for _ in 0..10 {
            if let Some(guard) = lock.try_lock() {
                return guard;
            }
            thread::yield_now();
        }
        // Sleep for at most ~1 ms
        thread::sleep(Duration::from_nanos(1 << i.min(20)));
        i += 1;
    }
}

#[cfg(not(feature = "spin"))]
#[inline]
fn wait_lock<'a, T>(lock: &'a Mutex<T>) -> MutexGuard<'a, T> {
    lock.lock().unwrap()
}

#[cfg(not(feature = "spin"))]
use std::sync::{Mutex, MutexGuard};

#[cfg(feature = "spin")]
type ChanLock<T> = Spinlock<T>;
#[cfg(not(feature = "spin"))]
type ChanLock<T> = Mutex<T>;


type SignalVec<T> = VecDeque<Arc<Hook<T, dyn signal::Signal>>>;
struct Chan<T> {
    sending: Option<(usize, SignalVec<T>)>,
    queue: VecDeque<T>,
    waiting: SignalVec<T>,
}

impl<T> Chan<T> {
    fn pull_pending(&mut self, pull_extra: bool) {
        if let Some((cap, sending)) = &mut self.sending {
            let effective_cap = *cap + pull_extra as usize;

            while self.queue.len() < effective_cap {
                if let Some(s) = sending.pop_front() {
                    let (msg, signal) = s.fire_recv();
                    signal.fire();
                    self.queue.push_back(msg);
                } else {
                    break;
                }
            }
        }
    }

    fn try_wake_receiver_if_pending(&mut self) {
        if !self.queue.is_empty() {
            while Some(false) == self.waiting.pop_front().map(|s| s.fire_nothing()) {}
        }
    }
}

struct Shared<T> {
    chan: ChanLock<Chan<T>>,
    disconnected: AtomicBool,
    sender_count: AtomicUsize,
    receiver_count: AtomicUsize,
}

impl<T> Shared<T> {
    fn new(cap: Option<usize>) -> Self {
        Self {
            chan: ChanLock::new(Chan {
                sending: cap.map(|cap| (cap, VecDeque::new())),
                queue: VecDeque::new(),
                waiting: VecDeque::new(),
            }),
            disconnected: AtomicBool::new(false),
            sender_count: AtomicUsize::new(1),
            receiver_count: AtomicUsize::new(1),
        }
    }

    fn send<S: Signal, R: From<Result<(), TrySendTimeoutError<T>>>>(
        &self,
        msg: T,
        should_block: bool,
        make_signal: impl FnOnce(T) -> Arc<Hook<T, S>>,
        do_block: impl FnOnce(Arc<Hook<T, S>>) -> R,
    ) -> R {
        let mut chan = wait_lock(&self.chan);

        if self.is_disconnected() {
            Err(TrySendTimeoutError::Disconnected(msg)).into()
        } else if !chan.waiting.is_empty() {
            let mut msg = Some(msg);

            loop {
                let slot = chan.waiting.pop_front();
                match slot.as_ref().map(|r| r.fire_send(msg.take().unwrap())) {
                    // No more waiting receivers and msg in queue, so break out of the loop
                    None if msg.is_none() => break,
                    // No more waiting receivers, so add msg to queue and break out of the loop
                    None => {
                        chan.queue.push_back(msg.unwrap());
                        break;
                    }
                    Some((Some(m), signal)) => {
                        if signal.fire() {
                            // Was async and a stream, so didn't acquire the message. Wake another
                            // receiver, and do not yet push the message.
                            msg.replace(m);
                            continue;
                        } else {
                            // Was async and not a stream, so it did acquire the message. Push the
                            // message to the queue for it to be received.
                            chan.queue.push_back(m);
                            drop(chan);
                            break;
                        }
                    },
                    Some((None, signal)) => {
                        drop(chan);
                        signal.fire();
                        break; // Was sync, so it has acquired the message
                    },
                }
            }

            Ok(()).into()
        } else if chan.sending.as_ref().map(|(cap, _)| chan.queue.len() < *cap).unwrap_or(true) {
            chan.queue.push_back(msg);
            Ok(()).into()
        } else if should_block { // Only bounded from here on
            let hook = make_signal(msg);
            chan.sending.as_mut().unwrap().1.push_back(hook.clone());
            drop(chan);

            do_block(hook)
        } else {
            Err(TrySendTimeoutError::Full(msg)).into()
        }
    }

    fn send_sync(
        &self,
        msg: T,
        block: Option<Option<Instant>>,
    ) -> Result<(), TrySendTimeoutError<T>> {
        self.send(
            // msg
            msg,
            // should_block
            block.is_some(),
            // make_signal
            |msg| Hook::slot(Some(msg), SyncSignal::default()),
            // do_block
            |hook| if let Some(deadline) = block.unwrap() {
                hook.wait_deadline_send(&self.disconnected, deadline)
                    .or_else(|timed_out| {
                        if timed_out { // Remove our signal
                            let hook: Arc<Hook<T, dyn signal::Signal>> = hook.clone();
                            wait_lock(&self.chan).sending
                                .as_mut()
                                .unwrap().1
                                .retain(|s| s.signal().as_ptr() != hook.signal().as_ptr());
                        }
                        hook.try_take().map(|msg| if self.is_disconnected() {
                            Err(TrySendTimeoutError::Disconnected(msg))
                        } else {
                            Err(TrySendTimeoutError::Timeout(msg))
                        })
                        .unwrap_or(Ok(()))
                    })
            } else {
                hook.wait_send(&self.disconnected);

                match hook.try_take() {
                    Some(msg) => Err(TrySendTimeoutError::Disconnected(msg)),
                    None => Ok(()),
                }
            },
        )
    }

    fn recv<S: Signal, R: From<Result<T, TryRecvTimeoutError>>>(
        &self,
        should_block: bool,
        make_signal: impl FnOnce() -> Arc<Hook<T, S>>,
        do_block: impl FnOnce(Arc<Hook<T, S>>) -> R,
    ) -> R {
        let mut chan = wait_lock(&self.chan);
        chan.pull_pending(true);

        if let Some(msg) = chan.queue.pop_front() {
            drop(chan);
            Ok(msg).into()
        } else if self.is_disconnected() {
            drop(chan);
            Err(TryRecvTimeoutError::Disconnected).into()
        } else if should_block {
            let hook = make_signal();
            chan.waiting.push_back(hook.clone());
            drop(chan);

            do_block(hook)
        } else {
            drop(chan);
            Err(TryRecvTimeoutError::Empty).into()
        }
    }

    fn recv_sync(&self, block: Option<Option<Instant>>) -> Result<T, TryRecvTimeoutError> {
        self.recv(
            // should_block
            block.is_some(),
            // make_signal
            || Hook::slot(None, SyncSignal::default()),
            // do_block
            |hook| if let Some(deadline) = block.unwrap() {
                hook.wait_deadline_recv(&self.disconnected, deadline)
                    .or_else(|timed_out| {
                        if timed_out { // Remove our signal
                            let hook: Arc<Hook<T, dyn Signal>> = hook.clone();
                            wait_lock(&self.chan).waiting
                                .retain(|s| s.signal().as_ptr() != hook.signal().as_ptr());
                        }
                        match hook.try_take() {
                            Some(msg) => Ok(msg),
                            None => {
                                let disconnected = self.is_disconnected(); // Check disconnect *before* msg
                                if let Some(msg) = wait_lock(&self.chan).queue.pop_front() {
                                    Ok(msg)
                                } else if disconnected {
                                    Err(TryRecvTimeoutError::Disconnected)
                                } else {
                                    Err(TryRecvTimeoutError::Timeout)
                                }
                            },
                        }
                    })
            } else {
                hook.wait_recv(&self.disconnected)
                    .or_else(|| wait_lock(&self.chan).queue.pop_front())
                    .ok_or(TryRecvTimeoutError::Disconnected)
            },
        )
    }

    /// Disconnect anything listening on this channel (this will not prevent receivers receiving
    /// msgs that have already been sent)
    fn disconnect_all(&self) {
        self.disconnected.store(true, Ordering::Relaxed);

        let mut chan = wait_lock(&self.chan);
        chan.pull_pending(false);
        if let Some((_, sending)) = chan.sending.as_ref() {
            sending.iter().for_each(|hook| {
                hook.signal().fire();
            })
        }
        chan.waiting.iter().for_each(|hook| {
            hook.signal().fire();
        });
    }

    fn is_disconnected(&self) -> bool {
        self.disconnected.load(Ordering::SeqCst)
    }

    fn is_empty(&self) -> bool {
        self.len() == 0
    }

    fn is_full(&self) -> bool {
        self.capacity().map(|cap| cap == self.len()).unwrap_or(false)
    }

    fn len(&self) -> usize {
        let mut chan = wait_lock(&self.chan);
        chan.pull_pending(false);
        chan.queue.len()
    }

    fn capacity(&self) -> Option<usize> {
        wait_lock(&self.chan).sending.as_ref().map(|(cap, _)| *cap)
    }
}

/// A transmitting end of a channel.
pub struct Sender<T> {
    shared: Arc<Shared<T>>,
}

impl<T> Sender<T> {
    /// Attempt to send a value into the channel. If the channel is bounded and full, or all
    /// receivers have been dropped, an error is returned. If the channel associated with this
    /// sender is unbounded, this method has the same behaviour as [`Sender::send`].
    pub fn try_send(&self, msg: T) -> Result<(), TrySendError<T>> {
        self.shared.send_sync(msg, None).map_err(|err| match err {
            TrySendTimeoutError::Full(msg) => TrySendError::Full(msg),
            TrySendTimeoutError::Disconnected(msg) => TrySendError::Disconnected(msg),
            _ => unreachable!(),
        })
    }

    /// Send a value into the channel, returning an error if all receivers have been dropped.
    /// If the channel is bounded and is full, this method will block until space is available
    /// or all receivers have been dropped. If the channel is unbounded, this method will not
    /// block.
    pub fn send(&self, msg: T) -> Result<(), SendError<T>> {
        self.shared.send_sync(msg, Some(None)).map_err(|err| match err {
            TrySendTimeoutError::Disconnected(msg) => SendError(msg),
            _ => unreachable!(),
        })
    }

    /// Send a value into the channel, returning an error if all receivers have been dropped
    /// or the deadline has passed. If the channel is bounded and is full, this method will
    /// block until space is available, the deadline is reached, or all receivers have been
    /// dropped.
    pub fn send_deadline(&self, msg: T, deadline: Instant) -> Result<(), SendTimeoutError<T>> {
        self.shared.send_sync(msg, Some(Some(deadline))).map_err(|err| match err {
            TrySendTimeoutError::Disconnected(msg) => SendTimeoutError::Disconnected(msg),
            TrySendTimeoutError::Timeout(msg) => SendTimeoutError::Timeout(msg),
            _ => unreachable!(),
        })
    }

    /// Send a value into the channel, returning an error if all receivers have been dropped
    /// or the timeout has expired. If the channel is bounded and is full, this method will
    /// block until space is available, the timeout has expired, or all receivers have been
    /// dropped.
    pub fn send_timeout(&self, msg: T, dur: Duration) -> Result<(), SendTimeoutError<T>> {
        self.send_deadline(msg, Instant::now().checked_add(dur).unwrap())
    }

    /// Returns true if all receivers for this channel have been dropped.
    pub fn is_disconnected(&self) -> bool {
        self.shared.is_disconnected()
    }

    /// Returns true if the channel is empty.
    /// Note: Zero-capacity channels are always empty.
    pub fn is_empty(&self) -> bool {
        self.shared.is_empty()
    }

    /// Returns true if the channel is full.
    /// Note: Zero-capacity channels are always full.
    pub fn is_full(&self) -> bool {
        self.shared.is_full()
    }

    /// Returns the number of messages in the channel
    pub fn len(&self) -> usize {
        self.shared.len()
    }

    /// If the channel is bounded, returns its capacity.
    pub fn capacity(&self) -> Option<usize> {
        self.shared.capacity()
    }
}

impl<T> Clone for Sender<T> {
    /// Clone this sender. [`Sender`] acts as a handle to the ending a channel. Remaining channel
    /// contents will only be cleaned up when all senders and the receiver have been dropped.
    fn clone(&self) -> Self {
        self.shared.sender_count.fetch_add(1, Ordering::Relaxed);
        Self { shared: self.shared.clone() }
    }
}

impl<T> fmt::Debug for Sender<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Sender").finish()
    }
}

impl<T> Drop for Sender<T> {
    fn drop(&mut self) {
        // Notify receivers that all senders have been dropped if the number of senders drops to 0.
        if self.shared.sender_count.fetch_sub(1, Ordering::Relaxed) == 1 {
            self.shared.disconnect_all();
        }
    }
}

/// The receiving end of a channel.
///
/// Note: Cloning the receiver *does not* turn this channel into a broadcast channel.
/// Each message will only be received by a single receiver. This is useful for
/// implementing work stealing for concurrent programs.
pub struct Receiver<T> {
    shared: Arc<Shared<T>>,
}

impl<T> Receiver<T> {
    /// Attempt to fetch an incoming value from the channel associated with this receiver,
    /// returning an error if the channel is empty or if all senders have been dropped.
    pub fn try_recv(&self) -> Result<T, TryRecvError> {
        self.shared.recv_sync(None).map_err(|err| match err {
            TryRecvTimeoutError::Disconnected => TryRecvError::Disconnected,
            TryRecvTimeoutError::Empty => TryRecvError::Empty,
            _ => unreachable!(),
        })
    }

    /// Wait for an incoming value from the channel associated with this receiver, returning an
    /// error if all senders have been dropped.
    pub fn recv(&self) -> Result<T, RecvError> {
        self.shared.recv_sync(Some(None)).map_err(|err| match err {
            TryRecvTimeoutError::Disconnected => RecvError::Disconnected,
            _ => unreachable!(),
        })
    }

    /// Wait for an incoming value from the channel associated with this receiver, returning an
    /// error if all senders have been dropped or the deadline has passed.
    pub fn recv_deadline(&self, deadline: Instant) -> Result<T, RecvTimeoutError> {
        self.shared.recv_sync(Some(Some(deadline))).map_err(|err| match err {
            TryRecvTimeoutError::Disconnected => RecvTimeoutError::Disconnected,
            TryRecvTimeoutError::Timeout => RecvTimeoutError::Timeout,
            _ => unreachable!(),
        })
    }

    /// Wait for an incoming value from the channel associated with this receiver, returning an
    /// error if all senders have been dropped or the timeout has expired.
    pub fn recv_timeout(&self, dur: Duration) -> Result<T, RecvTimeoutError> {
        self.recv_deadline(Instant::now().checked_add(dur).unwrap())
    }

    /// Create a blocking iterator over the values received on the channel that finishes iteration
    /// when all senders have been dropped.
    ///
    /// You can also create a self-owned iterator with [`Receiver::into_iter`].
    pub fn iter(&self) -> Iter<T> {
        Iter { receiver: &self }
    }

    /// A non-blocking iterator over the values received on the channel that finishes iteration
    /// when all senders have been dropped or the channel is empty.
    pub fn try_iter(&self) -> TryIter<T> {
        TryIter { receiver: &self }
    }

    /// Take all msgs currently sitting in the channel and produce an iterator over them. Unlike
    /// `try_iter`, the iterator will not attempt to fetch any more values from the channel once
    /// the function has been called.
    pub fn drain(&self) -> Drain<T> {
        let mut chan = wait_lock(&self.shared.chan);
        chan.pull_pending(false);
        let queue = std::mem::take(&mut chan.queue);

        Drain { queue, _phantom: PhantomData }
    }

    /// Returns true if all senders for this channel have been dropped.
    pub fn is_disconnected(&self) -> bool {
        self.shared.is_disconnected()
    }

    /// Returns true if the channel is empty.
    /// Note: Zero-capacity channels are always empty.
    pub fn is_empty(&self) -> bool {
        self.shared.is_empty()
    }

    /// Returns true if the channel is full.
    /// Note: Zero-capacity channels are always full.
    pub fn is_full(&self) -> bool {
        self.shared.is_full()
    }

    /// Returns the number of messages in the channel.
    pub fn len(&self) -> usize {
        self.shared.len()
    }

    /// If the channel is bounded, returns its capacity.
    pub fn capacity(&self) -> Option<usize> {
        self.shared.capacity()
    }
}

impl<T> Clone for Receiver<T> {
    /// Clone this receiver. [`Receiver`] acts as a handle to the ending a channel. Remaining
    /// channel contents will only be cleaned up when all senders and the receiver have been
    /// dropped.
    ///
    /// Note: Cloning the receiver *does not* turn this channel into a broadcast channel.
    /// Each message will only be received by a single receiver. This is useful for
    /// implementing work stealing for concurrent programs.
    fn clone(&self) -> Self {
        self.shared.receiver_count.fetch_add(1, Ordering::Relaxed);
        Self { shared: self.shared.clone() }
    }
}

impl<T> fmt::Debug for Receiver<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Receiver").finish()
    }
}

impl<T> Drop for Receiver<T> {
    fn drop(&mut self) {
        // Notify senders that all receivers have been dropped if the number of receivers drops
        // to 0.
        if self.shared.receiver_count.fetch_sub(1, Ordering::Relaxed) == 1 {
            self.shared.disconnect_all();
        }
    }
}

/// This exists as a shorthand for [`Receiver::iter`].
impl<'a, T> IntoIterator for &'a Receiver<T> {
    type Item = T;
    type IntoIter = Iter<'a, T>;

    fn into_iter(self) -> Self::IntoIter {
        Iter { receiver: self }
    }
}

impl<T> IntoIterator for Receiver<T> {
    type Item = T;
    type IntoIter = IntoIter<T>;

    /// Creates a self-owned but semantically equivalent alternative to [`Receiver::iter`].
    fn into_iter(self) -> Self::IntoIter {
        IntoIter { receiver: self }
    }
}

/// An iterator over the msgs received from a channel.
pub struct Iter<'a, T> {
    receiver: &'a Receiver<T>,
}

impl<'a, T> Iterator for Iter<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        self.receiver.recv().ok()
    }
}

/// An non-blocking iterator over the msgs received from a channel.
pub struct TryIter<'a, T> {
    receiver: &'a Receiver<T>,
}

impl<'a, T> Iterator for TryIter<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        self.receiver.try_recv().ok()
    }
}

/// An fixed-sized iterator over the msgs drained from a channel.
#[derive(Debug)]
pub struct Drain<'a, T> {
    queue: VecDeque<T>,
    /// A phantom field used to constrain the lifetime of this iterator. We do this because the
    /// implementation may change and we don't want to unintentionally constrain it. Removing this
    /// lifetime later is a possibility.
    _phantom: PhantomData<&'a ()>,
}

impl<'a, T> Iterator for Drain<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        self.queue.pop_front()
    }
}

impl<'a, T> ExactSizeIterator for Drain<'a, T> {
    fn len(&self) -> usize {
        self.queue.len()
    }
}

/// An owned iterator over the msgs received from a channel.
pub struct IntoIter<T> {
    receiver: Receiver<T>,
}

impl<T> Iterator for IntoIter<T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        self.receiver.recv().ok()
    }
}

/// Create a channel with no maximum capacity.
///
/// Create an unbounded channel with a [`Sender`] and [`Receiver`] connected to each end respectively. Values sent in
/// one end of the channel will be received on the other end. The channel is thread-safe, and both [`Sender`] and
/// [`Receiver`] may be sent to or shared between threads as necessary. In addition, both [`Sender`] and [`Receiver`]
/// may be cloned.
///
/// # Examples
/// ```
/// let (tx, rx) = flume::unbounded();
///
/// tx.send(42).unwrap();
/// assert_eq!(rx.recv().unwrap(), 42);
/// ```
pub fn unbounded<T>() -> (Sender<T>, Receiver<T>) {
    let shared = Arc::new(Shared::new(None));
    (
        Sender { shared: shared.clone() },
        Receiver { shared },
    )
}

/// Create a channel with a maximum capacity.
///
/// Create a bounded channel with a [`Sender`] and [`Receiver`] connected to each end respectively. Values sent in one
/// end of the channel will be received on the other end. The channel is thread-safe, and both [`Sender`] and
/// [`Receiver`] may be sent to or shared between threads as necessary. In addition, both [`Sender`] and [`Receiver`]
/// may be cloned.
///
/// Unlike an [`unbounded`] channel, if there is no space left for new messages, calls to
/// [`Sender::send`] will block (unblocking once a receiver has made space). If blocking behaviour
/// is not desired, [`Sender::try_send`] may be used.
///
/// Like `std::sync::mpsc`, `flume` supports 'rendezvous' channels. A bounded queue with a maximum capacity of zero
/// will block senders until a receiver is available to take the value. You can imagine a rendezvous channel as a
/// ['Glienicke Bridge'](https://en.wikipedia.org/wiki/Glienicke_Bridge)-style location at which senders and receivers
/// perform a handshake and transfer ownership of a value.
///
/// # Examples
/// ```
/// let (tx, rx) = flume::bounded(32);
///
/// for i in 1..33 {
///     tx.send(i).unwrap();
/// }
/// assert!(tx.try_send(33).is_err());
///
/// assert_eq!(rx.try_iter().sum::<u32>(), (1..33).sum());
/// ```
pub fn bounded<T>(cap: usize) -> (Sender<T>, Receiver<T>) {
    let shared = Arc::new(Shared::new(Some(cap)));
    (
        Sender { shared: shared.clone() },
        Receiver { shared },
    )
}