Mutex 似乎没有正确锁定

Question

我刚开始学习互斥。我认为下面的程序 return 总共 1000，但我得到的结果各不相同，所以我认为我做错了什么...

package main

import (
    "fmt"
    "sync"
)

var total int
var locker sync.RWMutex

func add() {
    for x := 1; x <= 100; x++ {
        locker.Lock()
        total += 1
        locker.Unlock()
    }
}

func main() {
    for x := 1; x <= 10; x++ {
        go add()
    }
    fmt.Printf("Total is %v\n", total)
}

Answer 1

在检查结果之前，您不会等待您开始的任何 goroutine 完成。使用 WaitGroup 等待所有这些完成。

Answer 2

您有一场数据竞赛。因此，结果未定义。

package main

import (
    "fmt"
    "sync"
)

var total int
var locker sync.RWMutex

func add() {
    for x := 1; x <= 100; x++ {
        locker.Lock()
        total += 1
        locker.Unlock()
    }
}

func main() {
    for x := 1; x <= 10; x++ {
        go add()
    }
    fmt.Printf("Total is %v\n", total)
}

输出：

$ go run -race racer.go
==================
WARNING: DATA RACE
Read at 0x0000005ba408 by main goroutine:
  runtime.convT2E64()
      /home/peter/go/src/runtime/iface.go:335 +0x0
  main.main()
      /home/peter/src/racer.go:23 +0x84

Previous write at 0x0000005ba408 by goroutine 14:
  main.add()
      /home/peter/src/racer.go:14 +0x76

Goroutine 14 (running) created at:
  main.main()
      /home/peter/src/racer.go:21 +0x52
==================
Total is 960
Found 1 data race(s)
exit status 66
$

Answer 3

主函数returns在gorutines完成它们的工作之前，你应该添加sync.WaitGroup，这段代码如你所愿：https://play.golang.com/p/_OfrZae0soB

package main

import (
    "fmt"
    "sync"
)

var total int
var locker sync.RWMutex

func add(wg *sync.WaitGroup) {
    defer wg.Done()
    for x := 1; x <= 100; x++ {
        locker.Lock()
        total += 1
        locker.Unlock()
    }
}

func main() {
    var wg sync.WaitGroup
    for x := 1; x <= 10; x++ {
        wg.Add(1)
        go add(&wg)
    }
    wg.Wait()
    fmt.Printf("Total is %v\n", total)
}

Mutex 似乎没有正确锁定

Mutex does not seem to be locking properly

concurrency

mutex

go