Advanced synchronisation block with throttling and cancellation in Go by using channels

advanced-sync.go

package main

import (
	"fmt"
	"math/rand"
	"time"
)

func main() {
	// first one wins. set of a bunch of tasks and stop when the
	// first item meets the condition

	a := 20                // attempts
	b := make(chan int, 4) // buffer
	c := make(chan int)    // check
	d := make(chan int)    // done

	rand.Seed(time.Now().UTC().UnixNano())

	for i := 0; i < a; i++ {
		go func(i int) {
			select {
			case b <- 0:
				fmt.Printf("Running: %d\n", i)
				time.Sleep(2 * time.Second)
				c <- rand.Intn(8)
				<-b
			case <-d:
				fmt.Printf("Cancelling: %d\n", i)
				return
			}
		}(i)
	}

	for i := 0; i < a; i++ {
		v := <-c
		fmt.Printf("%d: ", v)
		if v > 6 {
			fmt.Printf("match\n")
			close(d)
			break
		} else {
			fmt.Printf("no match\n")
		}
	}

	fmt.Println("complete")
	close(b)
	close(c)
}

TODO: Show how to report errors with make(chan error)