Concurrency

Run has built-in support for concurrency through green threads. Use the run keyword to spawn a lightweight concurrent task — similar to goroutines in Go.

package main

use "fmt"
use "time"

fun say(msg: string) {
    for i in 0..3 {
        time.sleep(100)
        fmt.println(msg)
    }
}

pub fun main() {
    run say("hello")
    say("world")
}

The run say("hello") call starts say in a new green thread. The main function continues executing concurrently.

Spawning multiple tasks

You can spawn as many concurrent tasks as you need. The runtime schedules them across available threads.

package main

use "fmt"
use "time"

fun worker(id: int) {
    time.sleep(100)
    fmt.println("worker", id, "done")
}

pub fun main() {
    for i in 0..5 {
        run worker(i)
    }

    time.sleep(1000) // wait for workers to finish
}

To coordinate between concurrent tasks, use channels — covered in the next chapter.