Channels

Channels are the primary way to communicate between concurrent tasks in Run. They allow one task to send a value and another to receive it.

Creating channels

ch := alloc(chan[int])      // unbuffered channel
ch := alloc(chan[int], 10)  // buffered channel with capacity 10

Sending and receiving

Use <- to send and receive values.

package main

use "fmt"

fun producer(ch: chan int) {
    for i in 0..5 {
        ch <- i  // send
    }
}

pub fun main() {
    ch := alloc(chan[int], 10)

    run producer(ch)

    for i in 0..5 {
        val := <-ch  // receive
        fmt.println(val)
    }
}

or range over a channel:

package main

use "fmt"

fun producer(ch: chan int) {
    for i in 0..5 {
        ch <- i  // send
    }

    close(ch)
}

pub fun main() {
    ch := alloc(chan[int], 10)

    run producer(ch)

    for val in ch {
        fmt.println(val)
    }
}

Closing channels

Use close(ch) to close a channel. This signals to the receiver that no more values will be sent.

ch := alloc(chan[int])
close(ch)

Unbuffered channels

An unbuffered channel synchronizes the sender and receiver — the sender blocks until the receiver is ready, and vice versa. This makes unbuffered channels useful for direct handoffs between tasks.

Buffered channels

A buffered channel allows sends to proceed without blocking until the buffer is full. This is useful when the sender and receiver run at different speeds.

ch := alloc(chan[string], 5)
ch <- "hello"  // does not block (buffer has space)