fibre 0.3.3

High-performance, memory-efficient sync/async channels built for real-time, low-overhead communication in concurrent Rust applications.
Documentation 
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

// src/mpmc/async_impl.rs
//! Implementation of the asynchronous Future-based send and receive logic.

use futures_core::Stream;

use super::core::{AsyncWaiter, WaiterData};
use super::{AsyncReceiver, AsyncSender};
use crate::error::{SendError, TryRecvError, TrySendError};
use crate::RecvError;

use core::marker::PhantomPinned;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};

// --- SendFuture ---

/// A future that completes when a value has been sent to the MPMC channel.
#[must_use = "futures do nothing unless you .await or poll them"]
#[derive(Debug)]
pub struct SendFuture<'a, T: Send> {
  sender: &'a AsyncSender<T>,
  // The item is wrapped in an Option so it can be taken during the poll.
  item: Option<T>,
  _phantom: PhantomPinned,
}

impl<'a, T: Send> SendFuture<'a, T> {
  pub(super) fn new(sender: &'a AsyncSender<T>, item: T) -> Self {
    Self {
      sender,
      item: Some(item),
      _phantom: PhantomPinned,
    }
  }
}

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

  fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
    let this = unsafe { self.as_mut().get_unchecked_mut() };
    'poll_loop: loop {
      // If the item has already been sent, the future is complete.
      if this.item.is_none() {
        // This can happen if poll is called again after it has already completed.
        return Poll::Ready(Ok(()));
      }

      // --- Phase 1: Try to send without parking ---
      let item_to_send = this.item.take().unwrap();
      match this.sender.shared.try_send_core(item_to_send) {
        Ok(()) => {
          return Poll::Ready(Ok(())); // Success!
        }
        Err(TrySendError::Full(returned_item)) => {
          // Channel is full, must park. Put the item back.
          this.item = Some(returned_item);
        }
        Err(TrySendError::Closed(_)) => {
          return Poll::Ready(Err(SendError::Closed));
        }
        Err(TrySendError::Sent(_)) => unreachable!(),
      }

      // --- Phase 2: Prepare to park ---
      let is_rendezvous = this.sender.shared.capacity == 0;

      // --- Phase 3: Lock, re-check, and commit to parking ---
      {
        let mut guard = this.sender.shared.internal.lock();

        // Re-check under lock. State might have changed.
        if !guard.waiting_async_receivers.is_empty()
          || !guard.waiting_sync_receivers.is_empty()
          || (this.sender.shared.capacity > 0 && guard.queue.len() < this.sender.shared.capacity)
        {
          drop(guard);
          continue 'poll_loop; // Retry immediately.
        }

        if guard.receiver_count == 0 {
          this.item = None; // Drop the item.
          return Poll::Ready(Err(SendError::Closed));
        }

        // Safe to park. Create the waiter and add it to the async queue.
        let waiter = AsyncWaiter {
          waker: cx.waker().clone(),
          data: if is_rendezvous {
            Some(WaiterData::SenderItem(this.item.take()))
          } else {
            None
          },
        };
        guard.waiting_async_senders.push_back(waiter);
        return Poll::Pending;
      }
    }
  }
}

/// A future that completes when a value has been received from the MPMC channel.
#[must_use = "futures do nothing unless you .await or poll them"]
#[derive(Debug)]
pub struct RecvFuture<'a, T: Send> {
  receiver: &'a AsyncReceiver<T>,
}

impl<'a, T: Send> RecvFuture<'a, T> {
  pub(super) fn new(receiver: &'a AsyncReceiver<T>) -> Self {
    Self { receiver }
  }
}

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

  fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
    self.receiver.shared.poll_recv_internal(cx)
  }
}

impl<T: Send> Stream for AsyncReceiver<T> {
  type Item = T;

  fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
    // Delegate to the internal poll function and map the Result to an Option.
    match self.shared.poll_recv_internal(cx) {
      Poll::Ready(Ok(value)) => Poll::Ready(Some(value)),
      Poll::Ready(Err(_)) => Poll::Ready(None), // Disconnected
      Poll::Pending => Poll::Pending,
    }
  }
}