Go routines with manual yielding.

t.go

package main;

import "fmt"
import "runtime"

func main() {
    runtime.GOMAXPROCS(1)

    a := make(chan bool)
    b := make(chan bool)

    go func() {
        fmt.Println("A")
        runtime.Gosched()
        fmt.Println("B")
        runtime.Gosched()
        fmt.Println("C")
        a <- true
    }()

    go func() {
        fmt.Println("D")
        runtime.Gosched()
        fmt.Println("E")
        runtime.Gosched()
        fmt.Println("F")
        b <- true
    }()
    
    <- a
    <- b
}