如何锁定地图并修复数据竞争

Question

I'm trying to solve WARNING: DATA RACE here is the code:

package models

import (
  "sync"
  "time"
)
type Stats struct {
    sync.Mutex
    request map[int64]int
}

func (s *Stats) PutRequest() {
  s.Lock()
  s.request[time.Now().Unix()]++
  s.Unlock()
}
func (s *Stats) GetRequests() map[int64]int {
    s.Lock()
    m := s.request
    s.Unlock()
    return m
 }
var Requests = Stats{
    sync.Mutex{},
    make(map[int64]int),
}

If i change Stats field request into integer then everithing works fine but not with map. How to correctly lock map in Go?

Answer 1

Use sync.RWMutex

func (s *Stats) PutRequest(ut int64) {
  s.Lock()
  defer s.Unlock()
  s.request[ut]++
}

---

func (s *Stats)  GetRequests() map[int64]int {
    s.RLock()
    defer s.RUnlock()
    m := make(map[int64]int, len(s.request))
    for k, v := range s.request {
        m[k] = v
    }
    return m
}

The following channel example can be interesting in this case. go by example - stateful goroutines

Anyway you need to copy the map before returning it.