为什么这个树行走功能会死锁？

Question

I am going through the Tour of Go to refresh my memory, and am stumbling on the Equivalent Binary Trees exercise. I have written some code to traverse a binary tree that looks like it should work.

package main

import (
    "golang.org/x/tour/tree"
    "fmt"
)

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
    if t == nil {
        return
    }
    ch <- t.Value
    Walk(t.Left, ch)
    Walk(t.Right, ch)
}

func main() {
    ch := make(chan int, 10)
    go Walk(tree.New(3), ch)
    for v := range ch {
        fmt.Printf("%q", v)
    }
}

When I run the above code I'm getting the following error:

'\x1e''\x0f''\t''\x03''\x06''\f''\x15''\x12''\x1b''\x18'fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan receive]:
main.main()
    /Users/james/src/local/go-sandbox/main.go:22 +0x115

Process finished with exit code 2

I am wondering why it is deadlocking? It looks like it does print out some garbage before this happens.

Answer 1

You must close the channel so range loop over it will terminate:

func main() {
    ch := make(chan int, 10)
    go func() {
        Walk(tree.New(3), ch)
        close(ch)
    }()
    for v := range ch {
        fmt.Printf("%q", v)
    }
}