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go 笔试题精选
高并发情况下，map常见问题分析 代码如下，正确的是（）
```go
package main
func main() {
map := make(map[int]int)
for i := 0; i < 100000; i {
go writemap(map, i, i)
go readmap(map, i)
}
}
func readmap(map map[int]int, key int) int {
return map[key]
}
func writemap(map map[int]int, key int, value int) {
map[key] = value
}
```
★★★
正确答案是：c
正确率：98%
解析：
官方解释：
maps are not safe for concurrent use: it’s not defined what happens when you read and write to them simultaneously. if you need to read from and write to a map from concurrently executing goroutines, the accesses must be mediated by some kind of synchronization mechanism. one common way to protect maps is with sync.rwmutex.
大致意思就是说，并发访问map是不安全的，会出现未定义行为，导致程序退出。所以如果希望在多协程s)中并发访问map，必须提供某种同步机制，一般情况下通过读写锁sync.rwmutex实现对map的并发访问控制，将map和sync.rwmutex封装一下，可以实现对map的安全并发访问。
同时go1.9版本之后，已经支持，sync包下：
func (m *map) delete(key interface{})
func (m *map) load(key interface{}) (value interface{}, ok bool)
func (m *map) loadorstore(key, value interface{}) (actual interface{}, loaded bool)
func (m *map) range(f func(key, value interface{}) bool)
func (m *map) store(key, value interface{})
