golang 中的 len() 线程安全吗？

pet*_*rSO 6

这是一个竞争条件。结果是不确定的。例如，

racer.go

package main

func main() {
    m := make(map[int]int)
    l := 0
    go func() {
        for {
            l = len(m)
        }
    }()
    for i := 0; i < 10000; i++ {
        m[i] = i
    }
}

输出：

$ go run -race racer.go
==================
WARNING: DATA RACE
Read at 0x00c00008e000 by goroutine 5:
  main.main.func1()
      /home/peter/gopath/src/racer.go:8 +0x5f

Previous write at 0x00c00008e000 by main goroutine:
  runtime.mapassign_fast64()
      /home/peter/go/src/runtime/map_fast64.go:92 +0x0
  main.main()
      /home/peter/gopath/src/racer.go:12 +0xba

Goroutine 5 (running) created at:
  main.main()
      /home/peter/gopath/src/racer.go:6 +0x92
==================
Found 1 data race(s)
exit status 66
$

参考：

golang 中的 len() 线程安全吗？ |