go中 panicrecoverdefer机制

go的defer机制-CSDN博客

常见panic场景

数组或切片越界，例如 s := make([]int, 3); fmt.Println(s[5]) 会引发 panic: runtime error: index out of range
空指针调用，例如 var p *Person; fmt.Println(p.Name) 会引发 panic: runtime error: invalid memory address or nil pointer dereference
过早关闭 HTTP 响应体，例如 resp, err := http.Get(url); defer resp.Body.Close(); if err != nil { return err } 会引发 panic: runtime error: invalid memory address or nil pointer dereference，因为如果 http.Get 出错，resp 可能是 nil
除以零，例如 x := 0; y := 1 / x 会引发 panic: runtime error: integer divide by zero
向已经关闭的 channel 发送或接收消息，例如 ch := make(chan int); close(ch); ch <- 1 会引发 panic: send on closed channel
重复关闭 channel，例如 ch := make(chan int); close(ch); close(ch) 会引发 panic: close of closed channel
关闭未初始化的 channel，例如 var ch chan int; close(ch) 会引发 panic: close of nil channel
未初始化的 map，例如 var m map[string]int; m["key"] = 1 会引发 panic: assignment to entry in nil map

recover常用的场景

panic 只会触发当前 Goroutine 的 defer；
recover 只有在 defer 中调用才会生效；

package mainimport "fmt"func main() {defer func() {if r := recover(); r != nil {fmt.Println("Recovered from panic:", r)}}()fmt.Println("Before panic")panic("Something went wrong")fmt.Println("After panic") // This line will not be executed
}运行结果Before panic
Recovered from panic: Something went wrong

defer，recover,panic，goroutine之间有什么联系呢

recover的作用域，recover在什么时候才会起作用

recover什么时候有效

recover未在defer内使用,是不会起任何作用

func main() {if r := recover(); r != nil {fmt.Println("Recovered from panic:", r)}fmt.Println("Before panic")panic("Something went wrong")fmt.Println("After panic") // This line will not be executed
}结果Before panic
panic: Something went wronggoroutine 1 [running]:
main.main()/Users/alan/GolandProjects/design-patterns/main.go:11 +0x78

recover必须搭配defer使用

recover在defer内使用才会起作用

package mainimport "fmt"func main() {defer func() {if r := recover(); r != nil {fmt.Println("Recovered from panic:", r)}}()fmt.Println("Before panic")panic("Something went wrong")fmt.Println("After panic") // This line will not be executed
}运行结果Before panic
Recovered from panic: Something went wrong

recove的作用域

recover在父协程

举个例子，一般使用chan的时候都是要在发送测关闭chan，我们在接受者通过控制超时

让函数提前退出，子协程一秒钟后退出


func main() {test()time.Sleep(time.Second * 10)
}
func test() {defer func() {if r := recover(); r != nil {fmt.Println("Recovered from panic:", r)}}()var ch = make(chan int)go get_data(ch)ctx, cancel := context.WithTimeout(context.Background(), time.Second)defer cancel()defer close(ch)select {case <-ch:returncase <-ctx.Done():return}
}
func get_data(ch chan int) {time.Sleep(time.Second * 2)ch <- 1
}

结果

我们发现没有recover住panic，子协程在test方法调用退出后，发生了panic，导致整个程序panic挂掉

recover,panic同子协程

相同的例子我们，我们在引起panic的协程内进行recover,结果函数正常recover后程序正常退出

func main() {test()time.Sleep(time.Second * 10)fmt.Println("时间到了 主函数也溜了")
}
func test() {defer func() {fmt.Println("test:我先溜了")}()var ch = make(chan int)go get_data(ch)ctx, cancel := context.WithTimeout(context.Background(), time.Second)defer cancel()defer close(ch)select {case <-ch:returncase <-ctx.Done():return}
}
func get_data(ch chan int) {defer func() {if r := recover(); r != nil {fmt.Println("Recovered from panic:", r)}}()time.Sleep(time.Second * 2)ch <- 1
}

结果