Struct thingbuf::mpsc::Sender

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pub struct Sender<T, R = DefaultRecycle> { /* private fields */ }

Available on crate feature alloc only.

Expand description

Asynchronously sends values to an associated Receiver.

Instances of this struct are created by the channel and with_recycle functions.

Implementations§

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impl<T, R> Sender<T, R>
where R: Recycle<T>,

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pub async fn send_ref(&self) -> Result<SendRef<'_, T>, Closed>

Reserves a slot in the channel to mutate in place, waiting until there is a free slot to write to.

This is similar to the send method, but, rather than taking a message by value to write to the channel, this method reserves a writable slot in the channel, and returns a SendRef that allows mutating the slot in place. If the Receiver end of the channel uses the Receiver::recv_ref or Receiver::poll_recv_ref methods for receiving from the channel, this allows allocations for channel messages to be reused in place.

§Errors

If the Receiver end of the channel has been dropped, this returns a Closed error.

§Examples

Sending formatted strings by writing them directly to channel slots, in place:

use thingbuf::mpsc;
use std::fmt::Write;

#[tokio::main]
async fn main() {
    let (tx, rx) = mpsc::channel::<String>(8);

    // Spawn a task that prints each message received from the channel:
    tokio::spawn(async move {
        for _ in 0..10 {
            let msg = rx.recv_ref().await.unwrap();
            println!("{}", msg);
        }
    });

    // Until the channel closes, write formatted messages to the channel.
    let mut count = 1;
    while let Ok(mut value) = tx.send_ref().await {
        // Writing to the `SendRef` will reuse the *existing* string
        // allocation in place.
        write!(value, "hello from message {}", count)
            .expect("writing to a `String` should never fail");
        count += 1;
    }
}

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pub async fn send(&self, val: T) -> Result<(), Closed<T>>

Sends a message by value, waiting until there is a free slot to write to.

This method takes the message by value, and replaces any previous value in the slot. This means that the channel will not function as an object pool while sending messages with send. This method is most appropriate when messages don’t own reusable heap allocations, or when the Receiver end of the channel must receive messages by moving them out of the channel by value (using the Receiver::recv method). When messages in the channel own reusable heap allocations (such as Strings or Vecs), and the Receiver doesn’t need to receive them by value, consider using send_ref instead, to enable allocation reuse.

§Errors

If the Receiver end of the channel has been dropped, this returns a Closed error containing the sent value.

§Examples

use thingbuf::mpsc;

#[tokio::main]
async fn main() {
    let (tx, rx) = mpsc::channel(8);

    // Spawn a task that prints each message received from the channel:
    tokio::spawn(async move {
        for _ in 0..10 {
            let msg = rx.recv().await.unwrap();
            println!("received message {}", msg);
        }
    });

    // Until the channel closes, write the current iteration to the channel.
    let mut count = 1;
    while tx.send(count).await.is_ok() {
        count += 1;
    }
}

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pub fn try_send_ref(&self) -> Result<SendRef<'_, T>, TrySendError>

Attempts to reserve a slot in the channel to mutate in place, without waiting for capacity.

This method differs from send_ref by returning immediately if the channel’s buffer is full or no Receiver exists. Compared with send_ref, this method has two failure cases instead of one (one for disconnection, one for a full buffer), and this method is not async, because it will never wait.

Like send_ref, this method returns a SendRef that may be used to mutate a slot in the channel’s buffer in place. Dropping the SendRef completes the send operation and makes the mutated value available to the Receiver.

§Errors

If the channel capacity has been reached (i.e., the channel has n buffered values where n is the argument passed to channel/with_recycle), then TrySendError::Full is returned. In this case, a future call to try_send may succeed if additional capacity becomes available.

If the receive half of the channel is closed (i.e., the Receiver handle was dropped), the function returns TrySendError::Closed. Once the channel has closed, subsequent calls to try_send_ref will never succeed.

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pub fn try_send(&self, val: T) -> Result<(), TrySendError<T>>

Attempts to send a message by value immediately, without waiting for capacity.

This method differs from send by returning immediately if the channel’s buffer is full or no Receiver exists. Compared with send, this method has two failure cases instead of one (one for disconnection, one for a full buffer), and this method is not async, because it will never wait.

§Errors

If the channel capacity has been reached (i.e., the channel has n buffered values where n is the argument passed to channel/with_recycle), then TrySendError::Full is returned. In this case, a future call to try_send may succeed if additional capacity becomes available.

If the receive half of the channel is closed (i.e., the Receiver handle was dropped), the function returns TrySendError::Closed. Once the channel has closed, subsequent calls to try_send will never succeed.

In both cases, the error includes the value passed to try_send.

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pub fn capacity(&self) -> usize

Returns the total capacity of the channel for this Sender. This includes both occupied and unoccupied entries.

To determine the channel’s remaining unoccupied capacity, use remaining instead.

§Examples

use thingbuf::mpsc::channel;

let (tx, _) = channel::<usize>(100);
assert_eq!(tx.capacity(), 100);

Even after sending several messages, the capacity remains the same:


let (tx, rx) = channel::<usize>(100);
*tx.try_send_ref().unwrap() = 1;
*tx.try_send_ref().unwrap() = 2;
*tx.try_send_ref().unwrap() = 3;

assert_eq!(tx.capacity(), 100);

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pub fn remaining(&self) -> usize

Returns the unoccupied capacity of the channel for this Sender (i.e., how many additional elements can be sent before the channel will be full).

This is equivalent to subtracting the channel’s len from its capacity.

§Examples

use thingbuf::mpsc::channel;

let (tx, rx) = channel::<usize>(100);
assert_eq!(tx.remaining(), 100);

*tx.try_send_ref().unwrap() = 1;
*tx.try_send_ref().unwrap() = 2;
*tx.try_send_ref().unwrap() = 3;
assert_eq!(tx.remaining(), 97);

let _ = rx.try_recv_ref().unwrap();
assert_eq!(tx.remaining(), 98)

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pub fn len(&self) -> usize

Returns the number of elements in the channel of this Sender.

To determine the channel’s remaining unoccupied capacity, use remaining instead.

§Examples

use thingbuf::mpsc::channel;

let (tx, rx) = channel::<usize>(100);
assert_eq!(tx.len(), 0);

*tx.try_send_ref().unwrap() = 1;
*tx.try_send_ref().unwrap() = 2;
*tx.try_send_ref().unwrap() = 3;
assert_eq!(tx.len(), 3);

let _ = rx.try_recv_ref().unwrap();
assert_eq!(tx.len(), 2);

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pub fn is_empty(&self) -> bool

Returns whether the number of elements in the channel of this Sender is 0.

§Examples

use thingbuf::mpsc::channel;
let (tx, rx) = channel::<usize>(100);
assert!(tx.is_empty());

*tx.try_send_ref().unwrap() = 1;

assert!(!tx.is_empty());