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
//! Futures and other types that allow asynchronous interaction with channels.

use std::{
    future::Future,
    pin::Pin,
    task::{Context, Poll, Waker},
    any::Any,
    ops::Deref,
};
use crate::*;
use futures_core::{stream::{Stream, FusedStream}, future::FusedFuture};
use futures_sink::Sink;
use spin1::Mutex as Spinlock;

struct AsyncSignal {
    waker: Spinlock<Waker>,
    woken: AtomicBool,
    stream: bool,
}

impl AsyncSignal {
    fn new(cx: &Context, stream: bool) -> Self {
        AsyncSignal {
            waker: Spinlock::new(cx.waker().clone()),
            woken: AtomicBool::new(false),
            stream,
        }
    }
}

impl Signal for AsyncSignal {
    fn fire(&self) -> bool {
        self.woken.store(true, Ordering::SeqCst);
        self.waker.lock().wake_by_ref();
        self.stream
    }

    fn as_any(&self) -> &(dyn Any + 'static) { self }
    fn as_ptr(&self) -> *const () { self as *const _ as *const () }
}

impl<T> Hook<T, AsyncSignal> {
    // Update the hook to point to the given Waker.
    // Returns whether the hook has been previously awakened
    fn update_waker(&self, cx_waker: &Waker) -> bool {
        let mut waker = self.1.waker.lock();
        let woken = self.1.woken.load(Ordering::SeqCst);
        if !waker.will_wake(cx_waker) {
            *waker = cx_waker.clone();

            // Avoid the edge case where the waker was woken just before the wakers were
            // swapped.
            if woken {
                cx_waker.wake_by_ref();
            }
        }
        woken
    }
}

#[derive(Clone)]
enum OwnedOrRef<'a, T> {
    Owned(T),
    Ref(&'a T),
}

impl<'a, T> Deref for OwnedOrRef<'a, T> {
    type Target = T;

    fn deref(&self) -> &T {
        match self {
            OwnedOrRef::Owned(arc) => &arc,
            OwnedOrRef::Ref(r) => r,
        }
    }
}

impl<T> Sender<T> {
    /// Asynchronously send a value into the channel, returning an error if all receivers have been
    /// dropped. If the channel is bounded and is full, the returned future will yield to the async
    /// runtime.
    ///
    /// In the current implementation, the returned future will not yield to the async runtime if the
    /// channel is unbounded. This may change in later versions.
    pub fn send_async(&self, item: T) -> SendFut<T> {
        SendFut {
            sender: OwnedOrRef::Ref(&self),
            hook: Some(SendState::NotYetSent(item)),
        }
    }

    /// Convert this sender into a future that asynchronously sends a single message into the channel,
    /// returning an error if all receivers have been dropped. If the channel is bounded and is full,
    /// this future will yield to the async runtime.
    ///
    /// In the current implementation, the returned future will not yield to the async runtime if the
    /// channel is unbounded. This may change in later versions.
    pub fn into_send_async<'a>(self, item: T) -> SendFut<'a, T> {
        SendFut {
            sender: OwnedOrRef::Owned(self),
            hook: Some(SendState::NotYetSent(item)),
        }
    }

    /// Create an asynchronous sink that uses this sender to asynchronously send messages into the
    /// channel. The sender will continue to be usable after the sink has been dropped.
    ///
    /// In the current implementation, the returned sink will not yield to the async runtime if the
    /// channel is unbounded. This may change in later versions.
    pub fn sink(&self) -> SendSink<'_, T> {
        SendSink(SendFut {
            sender: OwnedOrRef::Ref(&self),
            hook: None,
        })
    }

    /// Convert this sender into a sink that allows asynchronously sending messages into the channel.
    ///
    /// In the current implementation, the returned sink will not yield to the async runtime if the
    /// channel is unbounded. This may change in later versions.
    pub fn into_sink<'a>(self) -> SendSink<'a, T> {
        SendSink(SendFut {
            sender: OwnedOrRef::Owned(self),
            hook: None,
        })
    }
}

enum SendState<T> {
    NotYetSent(T),
    QueuedItem(Arc<Hook<T, AsyncSignal>>),
}

/// A future that sends a value into a channel.
///
/// Can be created via [`Sender::send_async`] or [`Sender::into_send_async`].
#[must_use = "futures/streams/sinks do nothing unless you `.await` or poll them"]
pub struct SendFut<'a, T> {
    sender: OwnedOrRef<'a, Sender<T>>,
    // Only none after dropping
    hook: Option<SendState<T>>,
}

impl<T> std::marker::Unpin for SendFut<'_, T> {}

impl<'a, T> SendFut<'a, T> {
    /// Reset the hook, clearing it and removing it from the waiting sender's queue. This is called
    /// on drop and just before `start_send` in the `Sink` implementation.
    fn reset_hook(&mut self) {
        if let Some(SendState::QueuedItem(hook)) = self.hook.take() {
            let hook: Arc<Hook<T, dyn Signal>> = hook;
            wait_lock(&self.sender.shared.chan).sending
                .as_mut()
                .unwrap().1
                .retain(|s| s.signal().as_ptr() != hook.signal().as_ptr());
        }
    }

    /// See [`Sender::is_disconnected`].
    pub fn is_disconnected(&self) -> bool {
        self.sender.is_disconnected()
    }

    /// See [`Sender::is_empty`].
    pub fn is_empty(&self) -> bool {
        self.sender.is_empty()
    }

    /// See [`Sender::is_full`].
    pub fn is_full(&self) -> bool {
        self.sender.is_full()
    }

    /// See [`Sender::len`].
    pub fn len(&self) -> usize {
        self.sender.len()
    }

    /// See [`Sender::capacity`].
    pub fn capacity(&self) -> Option<usize> {
        self.sender.capacity()
    }
}

impl<'a, T> Drop for SendFut<'a, T> {
    fn drop(&mut self) {
        self.reset_hook()
    }
}


impl<'a, T> Future for SendFut<'a, T> {
    type Output = Result<(), SendError<T>>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        if let Some(SendState::QueuedItem(hook)) = self.hook.as_ref() {
            if hook.is_empty() {
                Poll::Ready(Ok(()))
            } else if self.sender.shared.is_disconnected() {
                let item = hook.try_take();
                self.hook = None;
                match item {
                    Some(item) => Poll::Ready(Err(SendError(item))),
                    None => Poll::Ready(Ok(())),
                }
            } else {
                hook.update_waker(cx.waker());
                Poll::Pending
            }
        } else if let Some(SendState::NotYetSent(item)) = self.hook.take() {
            let this = self.get_mut();
            let (shared, this_hook) = (&this.sender.shared, &mut this.hook);

            shared.send(
                // item
                item,
                // should_block
                true,
                // make_signal
                |msg| Hook::slot(Some(msg), AsyncSignal::new(cx, false)),
                // do_block
                |hook| {
                    *this_hook = Some(SendState::QueuedItem(hook));
                    Poll::Pending
                },
            )
                .map(|r| r.map_err(|err| match err {
                    TrySendTimeoutError::Disconnected(msg) => SendError(msg),
                    _ => unreachable!(),
                }))
        } else { // Nothing to do
            Poll::Ready(Ok(()))
        }
    }
}

impl<'a, T> FusedFuture for SendFut<'a, T> {
    fn is_terminated(&self) -> bool {
        self.sender.shared.is_disconnected()
    }
}

/// A sink that allows sending values into a channel.
///
/// Can be created via [`Sender::sink`] or [`Sender::into_sink`].
pub struct SendSink<'a, T>(SendFut<'a, T>);

impl<'a, T> SendSink<'a, T> {
    /// Returns a clone of a sending half of the channel of this sink.
    pub fn sender(&self) -> &Sender<T> {
        &self.0.sender
    }

    /// See [`Sender::is_disconnected`].
    pub fn is_disconnected(&self) -> bool {
        self.0.is_disconnected()
    }

    /// See [`Sender::is_empty`].
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    /// See [`Sender::is_full`].
    pub fn is_full(&self) -> bool {
        self.0.is_full()
    }

    /// See [`Sender::len`].
    pub fn len(&self) -> usize {
        self.0.len()
    }

    /// See [`Sender::capacity`].
    pub fn capacity(&self) -> Option<usize> {
        self.0.capacity()
    }

    /// Returns whether the SendSinks are belong to the same channel.
    pub fn same_channel(&self, other: &Self) -> bool {
        self.sender().same_channel(other.sender())
    }
}

impl<'a, T> Sink<T> for SendSink<'a, T> {
    type Error = SendError<T>;

    fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
        Pin::new(&mut self.0).poll(cx)
    }

    fn start_send(mut self: Pin<&mut Self>, item: T) -> Result<(), Self::Error> {
        self.0.reset_hook();
        self.0.hook = Some(SendState::NotYetSent(item));

        Ok(())
    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
        Pin::new(&mut self.0).poll(cx) // TODO: A different strategy here?
    }

    fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Result<(), Self::Error>> {
        Pin::new(&mut self.0).poll(cx) // TODO: A different strategy here?
    }
}

impl<'a, T> Clone for SendSink<'a, T> {
    fn clone(&self) -> SendSink<'a, T> {
        SendSink(SendFut {
            sender: self.0.sender.clone(),
            hook: None,
        })
    }
}

impl<T> Receiver<T> {
    /// Asynchronously receive a value from the channel, returning an error if all senders have been
    /// dropped. If the channel is empty, the returned future will yield to the async runtime.
    pub fn recv_async(&self) -> RecvFut<'_, T> {
        RecvFut::new(OwnedOrRef::Ref(self))
    }

    /// Convert this receiver into a future that asynchronously receives a single message from the
    /// channel, returning an error if all senders have been dropped. If the channel is empty, this
    /// future will yield to the async runtime.
    pub fn into_recv_async<'a>(self) -> RecvFut<'a, T> {
        RecvFut::new(OwnedOrRef::Owned(self))
    }

    /// Create an asynchronous stream that uses this receiver to asynchronously receive messages
    /// from the channel. The receiver will continue to be usable after the stream has been dropped.
    pub fn stream(&self) -> RecvStream<'_, T> {
        RecvStream(RecvFut::new(OwnedOrRef::Ref(self)))
    }

    /// Convert this receiver into a stream that allows asynchronously receiving messages from the channel.
    pub fn into_stream<'a>(self) -> RecvStream<'a, T> {
        RecvStream(RecvFut::new(OwnedOrRef::Owned(self)))
    }
}

/// A future which allows asynchronously receiving a message.
///
/// Can be created via [`Receiver::recv_async`] or [`Receiver::into_recv_async`].
#[must_use = "futures/streams/sinks do nothing unless you `.await` or poll them"]
pub struct RecvFut<'a, T> {
    receiver: OwnedOrRef<'a, Receiver<T>>,
    hook: Option<Arc<Hook<T, AsyncSignal>>>,
}

impl<'a, T> RecvFut<'a, T> {
    fn new(receiver: OwnedOrRef<'a, Receiver<T>>) -> Self {
        Self {
            receiver,
            hook: None,
        }
    }

    /// Reset the hook, clearing it and removing it from the waiting receivers queue and waking
    /// another receiver if this receiver has been woken, so as not to cause any missed wakeups.
    /// This is called on drop and after a new item is received in `Stream::poll_next`.
    fn reset_hook(&mut self) {
        if let Some(hook) = self.hook.take() {
            let hook: Arc<Hook<T, dyn Signal>> = hook;
            let mut chan = wait_lock(&self.receiver.shared.chan);
            // We'd like to use `Arc::ptr_eq` here but it doesn't seem to work consistently with wide pointers?
            chan.waiting.retain(|s| s.signal().as_ptr() != hook.signal().as_ptr());
            if hook.signal().as_any().downcast_ref::<AsyncSignal>().unwrap().woken.load(Ordering::SeqCst) {
                // If this signal has been fired, but we're being dropped (and so not listening to it),
                // pass the signal on to another receiver
                chan.try_wake_receiver_if_pending();
            }
        }
    }

    fn poll_inner(
        self: Pin<&mut Self>,
        cx: &mut Context,
        stream: bool,
    ) -> Poll<Result<T, RecvError>> {
        if self.hook.is_some() {
            match self.receiver.shared.recv_sync(None) {
                Ok(msg) => return Poll::Ready(Ok(msg)),
                Err(TryRecvTimeoutError::Disconnected) => {
                    return Poll::Ready(Err(RecvError::Disconnected))
                }
                _ => (),
            }

            let hook = self.hook.as_ref().map(Arc::clone).unwrap();
            if hook.update_waker(cx.waker()) {
                // If the previous hook was awakened, we need to insert it back to the
                // queue, otherwise, it remains valid.
                wait_lock(&self.receiver.shared.chan)
                    .waiting
                    .push_back(hook);
            }
            // To avoid a missed wakeup, re-check disconnect status here because the channel might have
            // gotten shut down before we had a chance to push our hook
            if self.receiver.shared.is_disconnected() {
                // And now, to avoid a race condition between the first recv attempt and the disconnect check we
                // just performed, attempt to recv again just in case we missed something.
                Poll::Ready(
                    self.receiver
                        .shared
                        .recv_sync(None)
                        .map(Ok)
                        .unwrap_or(Err(RecvError::Disconnected)),
                )
            } else {
                Poll::Pending
            }
        } else {
            let mut_self = self.get_mut();
            let (shared, this_hook) = (&mut_self.receiver.shared, &mut mut_self.hook);

            shared.recv(
                // should_block
                true,
                // make_signal
                || Hook::trigger(AsyncSignal::new(cx, stream)),
                // do_block
                |hook| {
                    *this_hook = Some(hook);
                    Poll::Pending
                },
            )
                .map(|r| r.map_err(|err| match err {
                    TryRecvTimeoutError::Disconnected => RecvError::Disconnected,
                    _ => unreachable!(),
                }))
        }
    }

    /// See [`Receiver::is_disconnected`].
    pub fn is_disconnected(&self) -> bool {
        self.receiver.is_disconnected()
    }

    /// See [`Receiver::is_empty`].
    pub fn is_empty(&self) -> bool {
        self.receiver.is_empty()
    }

    /// See [`Receiver::is_full`].
    pub fn is_full(&self) -> bool {
        self.receiver.is_full()
    }

    /// See [`Receiver::len`].
    pub fn len(&self) -> usize {
        self.receiver.len()
    }

    /// See [`Receiver::capacity`].
    pub fn capacity(&self) -> Option<usize> {
        self.receiver.capacity()
    }
}

impl<'a, T> Drop for RecvFut<'a, T> {
    fn drop(&mut self) {
        self.reset_hook();
    }
}

impl<'a, T> Future for RecvFut<'a, T> {
    type Output = Result<T, RecvError>;

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        self.poll_inner(cx, false) // stream = false
    }
}

impl<'a, T> FusedFuture for RecvFut<'a, T> {
    fn is_terminated(&self) -> bool {
        self.receiver.shared.is_disconnected() && self.receiver.shared.is_empty()
    }
}

/// A stream which allows asynchronously receiving messages.
///
/// Can be created via [`Receiver::stream`] or [`Receiver::into_stream`].
pub struct RecvStream<'a, T>(RecvFut<'a, T>);

impl<'a, T> RecvStream<'a, T> {
    /// See [`Receiver::is_disconnected`].
    pub fn is_disconnected(&self) -> bool {
        self.0.is_disconnected()
    }

    /// See [`Receiver::is_empty`].
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    /// See [`Receiver::is_full`].
    pub fn is_full(&self) -> bool {
        self.0.is_full()
    }

    /// See [`Receiver::len`].
    pub fn len(&self) -> usize {
        self.0.len()
    }

    /// See [`Receiver::capacity`].
    pub fn capacity(&self) -> Option<usize> {
        self.0.capacity()
    }

    /// Returns whether the SendSinks are belong to the same channel.
    pub fn same_channel(&self, other: &Self) -> bool {
        self.0.receiver.same_channel(&*other.0.receiver)
    }
}

impl<'a, T> Clone for RecvStream<'a, T> {
    fn clone(&self) -> RecvStream<'a, T> {
        RecvStream(RecvFut::new(self.0.receiver.clone()))
    }
}

impl<'a, T> Stream for RecvStream<'a, T> {
    type Item = T;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        match Pin::new(&mut self.0).poll_inner(cx, true) { // stream = true
            Poll::Pending => Poll::Pending,
            Poll::Ready(item) => {
                self.0.reset_hook();
                Poll::Ready(item.ok())
            }
        }
    }
}

impl<'a, T> FusedStream for RecvStream<'a, T> {
    fn is_terminated(&self) -> bool {
        self.0.is_terminated()
    }
}