package main

import (
	"fmt"
)

func sum(a []int, c chan int) {
	s := 0
	for _, v := range a {
		s += v
	}
	c <- s
}

func main() {
	a := []int{7, 2, 8, -9, 4, 0}
	c := make(chan int)
	go sum(a[:len(a)/2], c)
	go sum(a[len(a)/2:], c)
	go sum(a, c)
	x, y, z := <-c, <-c, <-c
	fmt.Printf("%d %d %d\n", x, y, z)

	// panics with deadlock if buffer doesn't match reads from chan
	// throw: all goroutines are asleep - deadlock!
	c2 := make(chan int, 2)
	c2 <- 1
	c2 <- 2
	// must not do this without increasing buffer size: c2 <- 2
	fmt.Println(<-c2)
	fmt.Println(<-c2)

	// note that this chanel is buffered, and that we don't need to launch go 
	// routines
	c_buffered := make(chan int, 10)
	sum(a[:len(a)/2], c_buffered)
	sum(a[len(a)/2:], c_buffered)
	sum(a, c_buffered)
	x, y, z = <-c_buffered, <-c_buffered, <-c_buffered
	fmt.Printf("%d %d %d\n", x, y, z)
}