Share a go language mining pit: closure shared variable problem

The tutorial column of golang will share with you a go language pitfall: closure shared variable problem. I hope it will be helpful to friends in need!

Without further ado, let’s just look at the code and comments:

package mainimport (
    "fmt"
    "time")func main() {
    // 错误示例（打印出的结果是5个6）
    fmt.Println("closure buggy example...")
    for i := 1; i <= 5; i++ {
        // 每个goroutine共享一个变量，goroutine还没开始的时候，i已经变成了6
        go func() {
            fmt.Println(i)
        }()
    }
    time.Sleep(1 * time.Second)


    // 正确示例1：
    fmt.Println("normal example...")
    for i := 1; i <= 5; i++ {
        go func(i int) {   // 使用局部变量
            fmt.Println(i)
        }(i)
    }
    time.Sleep(1 * time.Second)

    // 正确示例2：
    fmt.Println("normal example 2...")
    for i := 1; i <= 5; i++ {
        i := i  // 为每个闭包创建一个变量
        go func() {
            fmt.Println(i)
        }()
    }
    time.Sleep(1 * time.Second)}

The results obtained by running are as follows:

closure buggy example...66666normal example...52134normal example 2...52134

See the code comments for reasons and solutions. The first example is an incorrect example, and the second and third examples are correct examples.

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