ConcurrentMap.md

fatal error: concurrent map read and map write

Go 语言中的 map 在并发情况下，只读是线程安全的，同时读写线程不安全。

• 解决方案一（通过读写锁sync.RWMutex实现对map的并发访问控制）

    package main
  
    import "sync"
  
    type SafeMap struct {
        sync.RWMutex
        Map map[int]int
    }
  
    func main() {
        safeMap := newSafeMap(10)
  
        for i := 0; i < 100000; i++ {
            go safeMap.writeMap(i, i)
            go safeMap.readMap(i)
        }
  
    }
  
    func newSafeMap(size int) *SafeMap {
        sm := new(SafeMap)
        sm.Map = make(map[int]int)
        return sm
  
    }
  
    func (sm *SafeMap) readMap(key int) int {
        sm.RLock()
        value := sm.Map[key]
        sm.RUnlock()
        return value
    }
  
    func (sm *SafeMap) writeMap(key int, value int) {
        sm.Lock()
        sm.Map[key] = value
        sm.Unlock()
    }
  

• 解决方案二（Go Version >= 1.9,直接使用sync.Map）

    package main
    import (
          "fmt"
          "sync"
    )
    func main() {
        var safeMap sync.Map
        
        // save key/value
        safeMap.Store("a", 1)
        safeMap.Store("b", 2)
        safeMap.Store("c", 3)
        
        // get value
        fmt.Println(safeMap.Load("c"))
        
        // remove key
        safeMap.Delete("b")
        
        // range map
        safeMap.Range(func(k, v interface{}) bool {
            fmt.Println("iterate:", k, v)
            return true
        })
    }