Go 原子操作int类型值

    sync/atomic 库提供了原子操作的支持，原子操作直接有底层CPU硬件支持，因而一般要比基于操作系统API的锁方式效率高些。对于int类型的增减操作有以下api:

// AddInt32 atomically adds delta to *addr and returns the new value.
func AddInt32(addr *int32, delta int32) (new int32)

// AddUint32 atomically adds delta to *addr and returns the new value.
// To subtract a signed positive constant value c from x, do AddUint32(&x, ^uint32(c-1)).
// In particular, to decrement x, do AddUint32(&x, ^uint32(0)).
func AddUint32(addr *uint32, delta uint32) (new uint32)

// AddInt64 atomically adds delta to *addr and returns the new value.
func AddInt64(addr *int64, delta int64) (new int64)

// AddUint64 atomically adds delta to *addr and returns the new value.
// To subtract a signed positive constant value c from x, do AddUint64(&x, ^uint64(c-1)).
// In particular, to decrement x, do AddUint64(&x, ^uint64(0)).
func AddUint64(addr *uint64, delta uint64) (new uint64)

第一个参数是指针类型，第二个参数是操作的值，类型要和第一个指针类型一致，返回值的类型和参数一致。

代码例子：

package main

import (
    "fmt"
    "sync"
    "sync/atomic"
)

func main() {
    var sum uint32 = 0
    var wg sync.WaitGroup
    for i := 0; i < 50; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            //sum += 1                 //1
            atomic.AddUint32(&sum, 1) //2
        }()
    }
    wg.Wait()
    fmt.Println(sum)
}

使用原子操作返回的结果是50，使用sum+=1，返回的结果不一定是50。

参考文章：https://www.kancloud.cn/liupengjie/go/571605