concurrentMap()函数Have WARNING: DATA RACE和 致命错误 ：concurrent map read and map write

concurrentStruct() 有警告：数据竞赛，但运行正常

为什么struct可以进行DATA RACE？

package main

import (
    "sync"
)

func main() {
    // concurrentMap()
    concurrentStruct()
    // concurrentStructWithMuLock()
}

type Metadata struct {
    mu  sync.RWMutex // 🔐
    key bool
}

// concurrentStruct 并发操作结构体
// concurrent read and write the struct
// go run -race  main.go   有 WARNING: DATA RACE，但是可以运行
// go run -race  main.go   It have WARNING: DATA RACE, But running ok
func concurrentStruct() {
    m := new(Metadata)

    for i := 0; i < 100000; i++ {
        go func(metadata *Metadata) {
            for {
                readValue := metadata.key
                if readValue {
                    metadata.key = false
                }
            }
        }(m)

        go func(metadata *Metadata) {
            for {
                metadata.key = true
            }
        }(m)
    }

    select {}
}

// concurrentStructWithMuLock  并发操作(使用了读写锁)结构体
// concurrent read and write the struct with RWMutex
// go run -race  main.go   没有 WARNING: DATA RACE
// go run -race  main.go   Don't have WARNING: DATA RACE, and running ok
func concurrentStructWithMuLock() {
    m := new(Metadata)

    go func(metadata *Metadata) {
        for {
            metadata.mu.Lock()
            readValue := metadata.key
            if readValue {
                metadata.key = false
            }
            metadata.mu.Unlock()
        }
    }(m)

    go func(metadata *Metadata) {
        for {
            metadata.mu.Lock()
            metadata.key = true
            metadata.mu.Unlock()
        }
    }(m)

    select {}
}

// concurrentMap 并发读写 Map
// concurrent read and write the map
// go run -race  main.go   有 WARNING: DATA RACE，不可运行，fatal error: concurrent map read and map write
// go run -race  main.go  Have WARNING: DATA RACE, And fatal error: concurrent map read and map write
func concurrentMap() {
    m := make(map[int]int)
    go func() {
        for {
            _ = m[1]
        }
    }()
    go func() {
        for {
            m[2] = 2
        }
    }()
    select {}
}