third_party/rust_crates/vendor/tokio-sync/src/mpsc/mod.rs

//! A multi-producer, single-consumer queue for sending values across
//! asynchronous tasks.
//!
//! Similar to `std`, channel creation provides [`Receiver`] and [`Sender`]
//! handles. [`Receiver`] implements `Stream` and allows a task to read values
//! out of the channel. If there is no message to read, the current task will be
//! notified when a new value is sent.  [`Sender`] implements the `Sink` trait
//! and allows sending messages into the channel. If the channel is at capacity,
//! the send is rejected and the task will be notified when additional capacity
//! is available. In other words, the channel provides backpressure.
//!
//! Unbounded channels are also available using the `unbounded_channel`
//! constructor.
//!
//! # Disconnection
//!
//! When all [`Sender`] handles have been dropped, it is no longer
//! possible to send values into the channel. This is considered the termination
//! event of the stream. As such, `Receiver::poll` returns `Ok(Ready(None))`.
//!
//! If the [`Receiver`] handle is dropped, then messages can no longer
//! be read out of the channel. In this case, all further attempts to send will
//! result in an error.
//!
//! # Clean Shutdown
//!
//! When the [`Receiver`] is dropped, it is possible for unprocessed messages to
//! remain in the channel. Instead, it is usually desirable to perform a "clean"
//! shutdown. To do this, the receiver first calls `close`, which will prevent
//! any further messages to be sent into the channel. Then, the receiver
//! consumes the channel to completion, at which point the receiver can be
//! dropped.
//!
//! [`Sender`]: struct.Sender.html
//! [`Receiver`]: struct.Receiver.html

mod block;
mod bounded;
mod chan;
mod list;
mod unbounded;

pub use self::bounded::{channel, Receiver, Sender};

pub use self::unbounded::{unbounded_channel, UnboundedReceiver, UnboundedSender};

pub mod error {
    //! Channel error types

    pub use super::bounded::{RecvError, SendError, TrySendError};

    pub use super::unbounded::{UnboundedRecvError, UnboundedSendError, UnboundedTrySendError};
}

/// The number of values a block can contain.
///
/// This value must be a power of 2. It also must be smaller than the number of
/// bits in `usize`.
#[cfg(target_pointer_width = "64")]
const BLOCK_CAP: usize = 32;

#[cfg(not(target_pointer_width = "64"))]
const BLOCK_CAP: usize = 16;