go-map的并发问题

go 语言的map是引用传递的、如果多个goroutine同时读写，必然导致冲突，所以一般我们在并发操作map的时候，一定要加锁，但是如果map里的value是还是map，那么并发操作这个value－ map是不是也一样回引起冲突呢？答案是：是的，go里所有map的并发操作都需要加锁，这样才不会引起冲突，见如下代码。我对map td操作加了锁，对得到的value－map进行了写操作，没有加锁，通过go run -race aa.go 依然可以检测到冲突，所以结论就是：并发读写操作go语言的任何一个map都需要加锁，这样才能防止冲突。

// filename: aa.go
import (
    "fmt"
    "sync"
    "time"
)

func main() {
    td := map[string]map[string]int{"info": {"age": 10}}
    var Lock sync.Mutex
    for i := 0; i < 2; i++ {
        go func(md map[string]map[string]int) {
            Lock.Lock()
            info := td["info"]
            Lock.Unlock()
            info["age"] = 100
            fmt.Println("info:", info["age"])
        }(td)
    }
    time.Sleep(1 * time.Second)
}

go 自带竞争检测机制调用如下命令

go run -race aa.go

结果如下：

info: 100
==================
WARNING: DATA RACE
Write at 0x00c4200162a0 by goroutine 6:
  runtime.mapassign()      /home/liuguirong/golang/go/src/runtime/hashmap.go:485 +0x0
  main.main.func1()
      /home/liuguirong/lgr/getiplib/src/aa.go:17 +0xef
Previous write at 0x00c4200162a0 by goroutine 7:
  runtime.mapassign()     /home/liuguirong/golang/go/src/runtime/hashmap.go:485 +0x0
  main.main.func1()
      /home/liuguirong/lgr/getiplib/src/aa.go:17 +0xef
Goroutine 6 (running) created at:
  main.main()
      /home/liuguirong/lgr/getiplib/src/aa.go:19 +0x1eb

Goroutine 7 (finished) created at:
  main.main()
      /home/liuguirong/lgr/getiplib/src/aa.go:19 +0x1eb
==================
==================
WARNING: DATA RACE
Write at 0x00c42005c3c8 by goroutine 6:
  main.main.func1()
      /home/liuguirong/lgr/getiplib/src/aa.go:17 +0x105

Previous write at 0x00c42005c3c8 by goroutine 7:
  main.main.func1()
      /home/liuguirong/lgr/getiplib/src/aa.go:17 +0x105

Goroutine 6 (running) created at:
  main.main()
      /home/liuguirong/lgr/getiplib/src/aa.go:19 +0x1eb

Goroutine 7 (finished) created at:
  main.main()
      /home/liuguirong/lgr/getiplib/src/aa.go:19 +0x1eb
==================
info: 100
Found 2 data race(s)
exit status 66