附录 D：让 Go panic 的十种方法

本章节有且仅有一个目的，那就是让你的 Go 程序遇到 panic。

D.1 数组/切片索引越界

func main() {
    names := []string{
        "煎鱼",
        "eddycjy",
        "Go 语言编程之旅",
    }
    name := names[len(names)]
    fmt.Printf("name: %s", name)
}

运行结果：

panic: runtime error: index out of range [3] with length 3
goroutine 1 [running]:
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:11 +0x1b

D.2 空指针调用

type User struct {
    Name string
}
func (u *User) GetName() string {
    return u.Name
}
func main() {
    s := &User{Name: "煎鱼"}
    s = nil
    s.GetName()
}

运行结果：

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1056f62]
goroutine 1 [running]:
main.(*User).GetName(...)
        /Users/eddycjy/go-application/awesomePanic/main.go:8
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:14 +0x2

D.3 过早关闭 HTTP 响应体

func main() {
    resp, err := http.Get("https://xxx")
    defer resp.Body.Close()
    if err != nil {
        log.Fatalf("http.Get err: %v", err)
    }
}

运行结果：

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x40 pc=0x123d4d3]
goroutine 1 [running]:
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:10 +0x63

D.4 除以零

func divide(a, b int) int {
    return a / b
}
func main() {
    divide(1, 0)
}

运行结果：

panic: runtime error: integer divide by zero
goroutine 1 [running]:
main.divide(...)
        /Users/eddycjy/go-application/awesomePanic/main.go:4
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:8 +0x12

D.5 向已关闭的通道发消息

func main() {
    ch := make(chan string, 1)
    ch <- "煎鱼"
    close(ch)
    ch <- "Go 语言编程之旅"
}

运行结果：

panic: send on closed channel
goroutine 1 [running]:
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:7 +0x7d

D.6 重复关闭通道

func main() {
    ch := make(chan string, 1)
    ch <- "Go 语言编程之旅"
    close(ch)
    close(ch)
}

运行结果：

panic: close of closed channel
goroutine 1 [running]:
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:7 +0x71

D.7 关闭未初始化的通道

func main() {
    var ch chan string
    close(ch)
}

运行结果：

panic: close of nil channel
goroutine 1 [running]:
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:5 +0x2a

D.8 未初始化 map

func main() {
    var m map[string]string
    m["Go 语言编程之旅"] = "一起用 Go 做项目"
}

运行结果：

panic: assignment to entry in nil map
goroutine 1 [running]:
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:5 +0x4b

D.9 跨协程的恐慌处理

func main() {
    go func() {
        defer func() {
            if err := recover(); err != nil {
                log.Fatalf("recover err: %v", err)
            }
        }()
        handle()
    }()
    time.Sleep(time.Second)
}
func handle() {
    go divide(1, 0)
}
func divide(a, b int) int {
    return a / b
}

运行结果：

panic: runtime error: integer divide by zero
goroutine 17 [running]:
main.divide(0x1, 0x0, 0x0)
        /Users/eddycjy/go-application/awesomePanic/main.go:34 +0x40
created by main.handle
        /Users/eddycjy/go-application/awesomePanic/main.go:30 +0x47

D.10 sync 计数为负值

func main() {
    wg := sync.WaitGroup{}
    wg.Add(-1)
    wg.Wait()
}

运行结果：

panic: sync: negative WaitGroup counter
goroutine 1 [running]:
sync.(*WaitGroup).Add(0xc000104000, 0xffffffffffffffff)
        /usr/local/Cellar/go/1.14/libexec/src/sync/waitgroup.go:74 +0x139
main.main()
        /Users/eddycjy/go-application/awesomePanic/main.go:7 +0x44

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