pub struct Receiver<T> { /* private fields */ }Expand description
The receiving half of Rust’s channel (or sync_channel) type.
This half can only be owned by one thread.
Messages sent to the channel can be retrieved using recv.
Examples
use std::sync::mpsc::channel;
use std::thread;
use std::time::Duration;
let (send, recv) = channel();
thread::spawn(move || {
send.send("Hello world!").unwrap();
thread::sleep(Duration::from_secs(2)); // block for two seconds
send.send("Delayed for 2 seconds").unwrap();
});
println!("{}", recv.recv().unwrap()); // Received immediately
println!("Waiting...");
println!("{}", recv.recv().unwrap()); // Received after 2 secondsImplementations
Attempts to return a pending value on this receiver without blocking.
This method will never block the caller in order to wait for data to become available. Instead, this will always return immediately with a possible option of pending data on the channel.
This is useful for a flavor of “optimistic check” before deciding to block on a receiver.
Compared with recv, this function has two failure cases instead of one
(one for disconnection, one for an empty buffer).
Examples
use std::sync::mpsc::{Receiver, channel};
let (_, receiver): (_, Receiver<i32>) = channel();
assert!(receiver.try_recv().is_err());Attempts to wait for a value on this receiver, returning an error if the corresponding channel has hung up.
This function will always block the current thread if there is no data
available and it’s possible for more data to be sent (at least one sender
still exists). Once a message is sent to the corresponding Sender
(or SyncSender), this receiver will wake up and return that
message.
If the corresponding Sender has disconnected, or it disconnects while
this call is blocking, this call will wake up and return Err to
indicate that no more messages can ever be received on this channel.
However, since channels are buffered, messages sent before the disconnect
will still be properly received.
Examples
use std::sync::mpsc;
use std::thread;
let (send, recv) = mpsc::channel();
let handle = thread::spawn(move || {
send.send(1u8).unwrap();
});
handle.join().unwrap();
assert_eq!(Ok(1), recv.recv());Buffering behavior:
use std::sync::mpsc;
use std::thread;
use std::sync::mpsc::RecvError;
let (send, recv) = mpsc::channel();
let handle = thread::spawn(move || {
send.send(1u8).unwrap();
send.send(2).unwrap();
send.send(3).unwrap();
drop(send);
});
// wait for the thread to join so we ensure the sender is dropped
handle.join().unwrap();
assert_eq!(Ok(1), recv.recv());
assert_eq!(Ok(2), recv.recv());
assert_eq!(Ok(3), recv.recv());
assert_eq!(Err(RecvError), recv.recv());Attempts to wait for a value on this receiver, returning an error if the
corresponding channel has hung up, or if it waits more than timeout.
This function will always block the current thread if there is no data
available and it’s possible for more data to be sent (at least one sender
still exists). Once a message is sent to the corresponding Sender
(or SyncSender), this receiver will wake up and return that
message.
If the corresponding Sender has disconnected, or it disconnects while
this call is blocking, this call will wake up and return Err to
indicate that no more messages can ever be received on this channel.
However, since channels are buffered, messages sent before the disconnect
will still be properly received.
Known Issues
There is currently a known issue (see #39364) that causes recv_timeout
to panic unexpectedly with the following example:
use std::sync::mpsc::channel;
use std::thread;
use std::time::Duration;
let (tx, rx) = channel::<String>();
thread::spawn(move || {
let d = Duration::from_millis(10);
loop {
println!("recv");
let _r = rx.recv_timeout(d);
}
});
thread::sleep(Duration::from_millis(100));
let _c1 = tx.clone();
thread::sleep(Duration::from_secs(1));Examples
Successfully receiving value before encountering timeout:
use std::thread;
use std::time::Duration;
use std::sync::mpsc;
let (send, recv) = mpsc::channel();
thread::spawn(move || {
send.send('a').unwrap();
});
assert_eq!(
recv.recv_timeout(Duration::from_millis(400)),
Ok('a')
);Receiving an error upon reaching timeout:
use std::thread;
use std::time::Duration;
use std::sync::mpsc;
let (send, recv) = mpsc::channel();
thread::spawn(move || {
thread::sleep(Duration::from_millis(800));
send.send('a').unwrap();
});
assert_eq!(
recv.recv_timeout(Duration::from_millis(400)),
Err(mpsc::RecvTimeoutError::Timeout)
);Attempts to wait for a value on this receiver, returning an error if the
corresponding channel has hung up, or if deadline is reached.
This function will always block the current thread if there is no data
available and it’s possible for more data to be sent. Once a message is
sent to the corresponding Sender (or SyncSender), then this
receiver will wake up and return that message.
If the corresponding Sender has disconnected, or it disconnects while
this call is blocking, this call will wake up and return Err to
indicate that no more messages can ever be received on this channel.
However, since channels are buffered, messages sent before the disconnect
will still be properly received.
Examples
Successfully receiving value before reaching deadline:
#![feature(deadline_api)]
use std::thread;
use std::time::{Duration, Instant};
use std::sync::mpsc;
let (send, recv) = mpsc::channel();
thread::spawn(move || {
send.send('a').unwrap();
});
assert_eq!(
recv.recv_deadline(Instant::now() + Duration::from_millis(400)),
Ok('a')
);Receiving an error upon reaching deadline:
#![feature(deadline_api)]
use std::thread;
use std::time::{Duration, Instant};
use std::sync::mpsc;
let (send, recv) = mpsc::channel();
thread::spawn(move || {
thread::sleep(Duration::from_millis(800));
send.send('a').unwrap();
});
assert_eq!(
recv.recv_deadline(Instant::now() + Duration::from_millis(400)),
Err(mpsc::RecvTimeoutError::Timeout)
);Returns an iterator that will block waiting for messages, but never
panic!. It will return None when the channel has hung up.
Examples
use std::sync::mpsc::channel;
use std::thread;
let (send, recv) = channel();
thread::spawn(move || {
send.send(1).unwrap();
send.send(2).unwrap();
send.send(3).unwrap();
});
let mut iter = recv.iter();
assert_eq!(iter.next(), Some(1));
assert_eq!(iter.next(), Some(2));
assert_eq!(iter.next(), Some(3));
assert_eq!(iter.next(), None);Returns an iterator that will attempt to yield all pending values.
It will return None if there are no more pending values or if the
channel has hung up. The iterator will never panic! or block the
user by waiting for values.
Examples
use std::sync::mpsc::channel;
use std::thread;
use std::time::Duration;
let (sender, receiver) = channel();
// nothing is in the buffer yet
assert!(receiver.try_iter().next().is_none());
thread::spawn(move || {
thread::sleep(Duration::from_secs(1));
sender.send(1).unwrap();
sender.send(2).unwrap();
sender.send(3).unwrap();
});
// nothing is in the buffer yet
assert!(receiver.try_iter().next().is_none());
// block for two seconds
thread::sleep(Duration::from_secs(2));
let mut iter = receiver.try_iter();
assert_eq!(iter.next(), Some(1));
assert_eq!(iter.next(), Some(2));
assert_eq!(iter.next(), Some(3));
assert_eq!(iter.next(), None);