Goroutine Closures

What will be printed when the code below is executed?And fix the issue to assure that len(m) is printed as 10. 

  1. package main
  3. import (
  4.     "sync"
  5. )
  7. const N = 10
  9. func main() {
  10.     m := make(map[int]int)
  12.     wg := &sync.WaitGroup{}
  13.     mu := &sync.Mutex{}
  14.     wg.Add(N)
  15.     for i := 0; i < N; i++ {
  16.         go func() {
  17.             defer wg.Done()
  18.             mu.Lock()
  19.             m[i] = i
  20.             mu.Unlock()
  21.         }()
  22.     }
  23.     wg.Wait()
  24.     println(len(m))
  25. }

Answer

  2. package main
  4. import (
  5.     "sync"
  6. )
  8. const N = 10
  10. func main() {
  11.     m := make(map[int]int)
  13.     wg := &sync.WaitGroup{}
  14.     mu := &sync.Mutex{}
  15.     wg.Add(N)
  16.     for i := 0; i < N; i++ {
  17.         go func(i int) {
  18.             defer wg.Done()
  19.             mu.Lock()
  20.             m[i] = i
  21.             mu.Unlock()
  22.         }(i)
  23.     }
  24.     wg.Wait()
  25.     println(len(m))
  26. }
  28.