go - panic 并从包裹中恢复

Question

我想弄清楚 panic() 和 recover() 是如何工作的..

日志包

package log

import (
    "fmt"
)

func Recover() {
    fmt.Println("Recovering!")
    if err := recover(); err != nil {
        fmt.Println("Error message recovered!")
    }
}

主包

package main

import (
    "fmt"
    log "www/pkg/log"
)

func main() {
    defer func() {
        log.Recover()
    }()

    panic("Fake error!")
}

输出

Recovering!
panic: Fake error!

为什么 错误消息已恢复! 从未打印过？

Answer 1

应用程序必须直接从延迟函数调用 recover 来处理 panic 。

specification讨论调用 recover 的延迟函数:

Suppose a function G defers a function D that calls recover and a panic occurs in a function on the same goroutine in which G is executing. When the running of deferred functions reaches D, the return value of D's call to recover will be the value passed to the call of panic.

它很微妙，但它不允许间接调用恢复。此外，关于 recover 的返回值的段落提到了延迟函数的直接调用:

The return value of recover is nil if any of the following conditions holds:

• recover was not called directly by a deferred function.

我最近被这个问题捕获了。由于规范非常简洁，有时需要仔细阅读才能找到一些要点。