如何应对外界的恐慌

Question

Look at the following code snippet.

package main

import "fmt"

func explode() {
    // Cause a panic.
    panic("WRONG")
}

func recovery() int {
    explode()
    defer func() {
        fmt.Println("Try to handle panic")
        if err := recover(); err != nil {
            fmt.Println("FIX")
            fmt.Println("ERR", err)
        }
    }()
    fmt.Println("Print value")
    return 100

}

func main() {
    // Handle errors in defer func with recover.
    fmt.Println(recovery())
}

As you can see code above, I fired a panic in the explode function and want to handle it in the recovery function. But the panic does not get caught, I've got runtime error

goroutine 1 [running]:
main.explode()
        D:/gocode/src/samples/panic1.go:7 +0x6b
main.recovery(0xc082002250)
        D:/gocode/src/samples/panic1.go:18 +0x26
main.main()
        D:/gocode/src/samples/panic1.go:27 +0x26

goroutine 2 [runnable]:
runtime.forcegchelper()
        c:/go/src/runtime/proc.go:90
runtime.goexit()
        c:/go/src/runtime/asm_amd64.s:2232 +0x1

goroutine 3 [runnable]:
runtime.bgsweep()
        c:/go/src/runtime/mgc0.go:82
runtime.goexit()
        c:/go/src/runtime/asm_amd64.s:2232 +0x1

goroutine 4 [runnable]:
runtime.runfinq()
        c:/go/src/runtime/malloc.go:712
runtime.goexit()
        c:/go/src/runtime/asm_amd64.s:2232 +0x1
exit status 2

How to catch the panic in the recory function?

Answer 1

If you call explode() first, the function that would handle the panic and try to recover is not yet registered (and never will be because you call panic inside explode()), so it won't be called and obviously it can't do its work.

You have to call defer first and then the explode() function:

defer func() {
    // recover() here, Your code omitted
}()
explode()

Try it on the Go Playground.