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本文次要钻研一下golang的panic与recover

panic与recover

recover在如下三种状况下返回nil

  • panic参数为nil
  • goroutine没有产生panic
  • recover不是在defer func中调用

实例

实例1

var fc func() stringfunc 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，因此产生runtime panic，而后被defer的recover捕捉

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捕捉了panic，defer1就捕捉不到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，"笼罩"了原始的panic，defer1捕捉的是最初一个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没有捕捉，产生的panic顺次显示了main panic及defer2 panic

输入

defer2 begin to panicdefer1panic: main panic        panic: defer2 panicgoroutine 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")}

输入

defer2 begin to panicdefer1panic: main panic        panic: defer2 panic        panic: defer3 panicgoroutine 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")}

输入

defer2 begin to panicdefer1panic: main panic        panic: defer2 panic [recovered]        panic: defer1 panic after recovergoroutine 1 [running]:main.panicAfterRecover.func1()        /defer.go:180 +0x10dpanic(0x10b2020, 0x10eaed0)        /usr/local/go/src/runtime/panic.go:969 +0x1b9main.panicAfterRecover.func2()        /defer.go:188 +0x95panic(0x10b2020, 0x10eaee0)        /usr/local/go/src/runtime/panic.go:969 +0x1b9main.panicAfterRecover()        /defer.go:191 +0x68main.main()        /defer.go:215 +0x25exit status 2

小结

  • recover必须在defer中调用才能够，多个defer呈现了panic没有recover，则panic信息会列出所有的painc信息
  • 如果defer也呈现了panic则若有被recover则recover的是最初一个panic，非defer的panic被"笼罩"
  • 如果defer的recover之后呈现了panic，则最初panic会呈现被recover的那个panic信息

doc

  • Handling_panics