聊聊golang的panic与recover

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本文主要研究一下golang的panic与recover

panic与recover

recover在如下三种情况下返回nil

• panic参数为nil
• goroutine没有发生panic
• recover不是在defer func中调用

实例

实例1

var fc func() string
func protect(g func() string) {
 defer func() {
 fmt.Println("done") // Println executes normally even if there is a panic
 if x := recover(); x != nil {
 fmt.Printf("run time panic: %v", x)
 }
 }()
 fmt.Println("start")
 fmt.Println(g())
}
func main() {
 protect(fc)
}

这里fc为nil,因而产生runtime panic,然后被defer的recover捕获

实例2

func deferRecover() {
 defer func() {
 fmt.Println("defer1: recover")
 if err := recover(); err != nil {
 fmt.Println(err)
 } else {
 fmt.Println("defer1 recover nil")
 }
 }()
 defer func() {
 fmt.Println("defer2: recover ")
 if err := recover(); err != nil {
 fmt.Println(err)
 }
 }()
 panic("manual panic")
 defer func() { 
 fmt.Println("never be executed") 
 }()
}

这里defer2捕获了panic,defer1就捕获不到panic了

实例3

func paincInDefer() {
 defer func() {
 fmt.Println("defer1 recover")
 if err := recover(); err != nil {
 // main panic is override by defer2 panic
 fmt.Println(err)
 } else {
 fmt.Println("defer1 recover nil")
 }
 }()
 defer func() {
 fmt.Println("defer2 begin to panic")
 panic("defer2 panic")
 }()
 panic("main panic")
}

这里defer2产生了panic,"覆盖"了原始的panic,defer1捕获的是最后一个panic即defer2产生的panic

实例4

func paincInDeferNotRecover() {
 defer func() {
 fmt.Println("defer1")
 }()
 defer func() {
 fmt.Println("defer2 begin to panic")
 panic("defer2 panic")
 }()
 panic("main panic")
}

这里defer2产生了panic,defer1没有捕获,产生的panic依次显示了main panic及defer2 panic

输出

defer2 begin to panic
defer1
panic: main panic
 panic: defer2 panic
goroutine 1 [running]:
main.paincInDeferNotRecover.func2()

实例5

func multiPaincInDefer() {
 defer func() {
 fmt.Println("defer1")
 panic("defer3 panic")
 }()
 defer func() {
 fmt.Println("defer2 begin to panic")
 panic("defer2 panic")
 }()
 panic("main panic")
}

输出

defer2 begin to panic
defer1
panic: main panic
 panic: defer2 panic
 panic: defer3 panic
goroutine 1 [running]:
main.multiPaincInDefer.func1()

实例6

func panicAfterRecover() {
 defer func() {
 fmt.Println("defer1")
 if err := recover(); err != nil {
 panic("defer1 panic after recover")
 } else {
 fmt.Println("defer1 recover nil")
 }
 }()
 defer func() {
 fmt.Println("defer2 begin to panic")
 panic("defer2 panic")
 }()
 panic("main panic")
}

输出

defer2 begin to panic
defer1
panic: main panic
 panic: defer2 panic [recovered]
 panic: defer1 panic after recover
goroutine 1 [running]:
main.panicAfterRecover.func1()
 /defer.go:180 +0x10d
panic(0x10b2020, 0x10eaed0)
 /usr/local/go/src/runtime/panic.go:969 +0x1b9
main.panicAfterRecover.func2()
 /defer.go:188 +0x95
panic(0x10b2020, 0x10eaee0)
 /usr/local/go/src/runtime/panic.go:969 +0x1b9
main.panicAfterRecover()
 /defer.go:191 +0x68
main.main()
 /defer.go:215 +0x25
exit status 2

小结

• recover必须在defer中调用才可以,多个defer出现了panic没有recover,则panic信息会列出所有的painc信息
• 如果defer也出现了panic则若有被recover则recover的是最后一个panic,非defer的panic被"覆盖"
• 如果defer的recover之后出现了panic,则最后panic会出现被recover的那个panic信息

doc

• Handling_panics

本文来自:简书

感谢作者:go4it

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