Map Mutex

Fix the issue below to avoid "concurrent map writes" error. 

  1. package main
  3. import (
  4.     "math/rand"
  5.     "sync"
  6. )
  8. const N = 10
  10. func main() {
  11.     m := make(map[int]int)
  13.     wg := &sync.WaitGroup{}
  14.     wg.Add(N)
  15.     for i := 0; i < N; i++ {
  16.         go func() {
  17.             defer wg.Done()
  18.             m[rand.Int()] = rand.Int()
  19.         }()
  20.     }
  21.     wg.Wait()
  22.     println(len(m))
  23. }

Answer

  2. package main
  4. import (
  5.     "math/rand"
  6.     "sync"
  7. )
  9. const N = 10
  11. func main() {
  12.     m := make(map[int]int)
  14.     wg := &sync.WaitGroup{}
  15.     mu := &sync.Mutex{}
  16.     wg.Add(N)
  17.     for i := 0; i < N; i++ {
  18.         go func() {
  19.             defer wg.Done()
  20.             mu.Lock()
  21.             m[rand.Int()] = rand.Int()
  22.             mu.Unlock()
  23.         }()
  24.     }
  25.     wg.Wait()
  26.     println(len(m))
  27. }
  29.