Question

http://play.golang.org/p/r92-KtQEGl

I am trying to execute this code. It throws a deadlock error.

What am I missing?

package main

import "tour/tree"
import "fmt"

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int){
    var temp chan int
    ch <- t.Value
    if t.Left!=nil{go Walk(t.Left,temp)}
    if t.Right!=nil{go Walk(t.Right,temp)}
    for i := range temp{
        ch <- i
    }
    close(ch)
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool

Answer 1

You need at least to initialize your channels (if the channel is nil, a range would block forever)

  var temp chan int = make(chan int)
  var ch chan int = make(chan int)

See http://play.golang.org/p/Gh8MZlyd3B (still deadlock but at least display results)

This version, using two temp channels, doesn’t deadlock: http://play.golang.org/p/KsnmKTgZ83

package main

import "tour/tree"
import "fmt"

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
    var temp1 chan int = make(chan int)
    var temp2 chan int = make(chan int)
    ch <- t.Value
    if t.Left != nil {
        go Walk(t.Left, temp1)
    }
    if t.Right != nil {
        go Walk(t.Right, temp2)
    }
    if t.Left != nil {
        for i := range temp1 {
            ch <- i
        }
    }
    if t.Right != nil {
        for i := range temp2 {
            ch <- i
        }
    }
    close(ch)
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool

func main() {
    var ch chan int = make(chan int)
    go Walk(tree.New(1), ch)
    for i := range ch {
        fmt.Println(i)
    }
}