title: Golang Goroutine leak
body: <pre><code>// Copyright 2012 The Go Authors.  All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // +build ignore
  
  package main
  
  import (
      "fmt"
  
      "code.google.com/p/go-tour/tree"
  )
  
  func walkImpl(t *tree.Tree, ch chan int) {
      if t == nil {
          return
      }
      walkImpl(t.Left, ch)
      ch &lt;- t.Value
      walkImpl(t.Right, ch)
  }
  
  // Walk walks the tree t sending all values
  // from the tree to the channel ch.
  func Walk(t *tree.Tree, ch chan int) {
      walkImpl(t, ch)
      // Need to close the channel here
      close(ch)
  }
  
  // Same determines whether the trees
  // t1 and t2 contain the same values.
  // NOTE: The implementation leaks goroutines when trees are different.
  // See binarytrees_quit.go for a better solution.
  func Same(t1, t2 *tree.Tree) bool {
      w1, w2 := make(chan int), make(chan int)
  
      go Walk(t1, w1)
      go Walk(t2, w2)
  
      for {
          v1, ok1 := &lt;-w1
          v2, ok2 := &lt;-w2
          if !ok1 || !ok2 {
              return ok1 == ok2
          }
          if v1 != v2 {
              return false
          }
      }
  }
  
  func main() {
      fmt.Print("tree.New(1) == tree.New(1): ")
      if Same(tree.New(1), tree.New(1)) {
          fmt.Println("PASSED")
      } else {
          fmt.Println("FAILED")
      }
  
      fmt.Print("tree.New(1) != tree.New(2): ")
      if !Same(tree.New(1), tree.New(2)) {
          fmt.Println("PASSED")
      } else {
          fmt.Println("FAILED")
      }
  }
  </code></pre>
  
  <p>In this code, a solution for <a href="http://tour.golang.org/concurrency/8" rel="nofollow">http://tour.golang.org/concurrency/8</a></p>
  
  <p>Why is there a comment on Same() func Same(t1, t2 *tree.Tree) bool saying that it leaks goroutines? How so? It also mentions a second file that fixes this: </p>
  
  <pre><code>// Copyright 2015 The Go Authors.  All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // +build ignore
  
  package main
  
  import (
      "fmt"
  
      "code.google.com/p/go-tour/tree"
  )
  
  func walkImpl(t *tree.Tree, ch, quit chan int) {
      if t == nil {
          return
      }
      walkImpl(t.Left, ch, quit)
      select {
      case ch &lt;- t.Value:
          // Value successfully sent.
      case &lt;-quit:
          return
      }
      walkImpl(t.Right, ch, quit)
  }
  
  // Walk walks the tree t sending all values
  // from the tree to the channel ch.
  func Walk(t *tree.Tree, ch, quit chan int) {
      walkImpl(t, ch, quit)
      close(ch)
  }
  
  // Same determines whether the trees
  // t1 and t2 contain the same values.
  func Same(t1, t2 *tree.Tree) bool {
      w1, w2 := make(chan int), make(chan int)
      quit := make(chan int)
      defer close(quit)
  
      go Walk(t1, w1, quit)
      go Walk(t2, w2, quit)
  
      for {
          v1, ok1 := &lt;-w1
          v2, ok2 := &lt;-w2
          if !ok1 || !ok2 {
              return ok1 == ok2
          }
          if v1 != v2 {
              return false
          }
      }
  }
  
  func main() {
      fmt.Print("tree.New(1) == tree.New(1): ")
      if Same(tree.New(1), tree.New(1)) {
          fmt.Println("PASSED")
      } else {
          fmt.Println("FAILED")
      }
  
      fmt.Print("tree.New(1) != tree.New(2): ")
      if !Same(tree.New(1), tree.New(2)) {
          fmt.Println("PASSED")
      } else {
          fmt.Println("FAILED")
      }
  }
  </code></pre>
  
  <p>How does it accomplish that? Where was this leak? (to test the code you will have to run it on <a href="http://tour.golang.org/concurrency/8" rel="nofollow">http://tour.golang.org/concurrency/8</a>). Very confused and would appreciate some help, thanks!</p>