3.7 Go panic 与 recover 学习笔记

1. panic — 触发程序崩溃panic立即中断当前函数的执行开始逐层退出unwind如果没有被 recover 捕获整个程序崩溃package mainimportfmtfuncdemonstratePanic(){fmt.Println(Before panic)panic(Something went wrong!)fmt.Println(After panic)// 这行永远不会执行}funcmain(){fmt.Println( demonstratePanic with recovery )func(){deferfunc(){ifr :recover();r!nil{fmt.Println(Caught panic from demonstratePanic:, r)}}()demonstratePanic()}()}执行结果demonstratePanic with recoveryBefore panic Caught panic from demonstratePanic: Something went wrong!要点panic(Something went wrong!)立即中断函数“After panic” 不会执行panic 会触发函数逐层退出unwind每一层的 defer 都会执行如果没有任何 recover 捕获程序崩溃并打印 panic 信息和堆栈追踪本例用匿名函数 defer/recover 包裹了 demonstratePanic所以 panic 被捕获程序继续运行panic 的适用场景不可恢复的错误如配置缺失、逻辑矛盾不要用于普通错误处理2. defer recover 捕获 panicrecover()只能在 defer 函数内调用用于捕获 panic 并恢复程序执行package mainimportfmtfunc safeDivide(a, b int)(result int){deferfunc(){ifr :recover();r!nil{fmt.Println(Recovered from panic:, r)result0// 设置 panic 情况下的返回值}}()ifb0{panic(division by zero)}returna / b}funcmain(){// 正常情况 fmt.Println( safeDivide normal case )result1 :safeDivide(10,2)fmt.Println(Result:, result1)// panic 情况 fmt.Println(\n safeDivide panic case )result2 :safeDivide(10,0)fmt.Println(Result:, result2)}执行结果safeDivide normalcaseResult:5safeDivide paniccaseRecovered from panic: division by zero Result:0要点recover()返回 panic 传入的值此处是字符串 “division by zero”如果没有 panic 则返回nilrecover只能在 defer 函数内调用直接调用 recover不在 defer 中永远返回 nilresult 0利用命名返回值result在 defer 中修改 panic 情况下的返回值正常情况recover()返回 nil不进入 if 分支result保持a/b 5panic 情况recover()返回 “division by zero”进入 if 分支result被设为 03. recover 捕获运行时 panic越界访问等recover 可以捕获 Go 运行时产生的 panic如数组越界、nil 指针等package mainimportfmtfunc processArray(arr[]int){deferfunc(){ifr :recover();r!nil{fmt.Println(Recovered from array access panic)}}()value :arr[10]// 如果 arr 长度11运行时 panic fmt.Println(Value at index 10:, value)}funcmain(){// 短数组越界 panic fmt.Println( processArray with short array )shortArr :[]int{1,2,3}processArray(shortArr)// 长数组正常访问 fmt.Println(\n processArray with long array )longArr :make([]int,15)fori :0;i15;i{longArr[i]i *10}processArray(longArr)}执行结果processArray with short arrayRecovered from array access panicprocessArray with long arrayValue at index10:100要点shortArr只有 3 个元素访问arr[10]导致运行时 panicindex out of rangelongArr有 15 个元素arr[10] 10010*10100正常输出recover 不区分 panic 来源无论是手动panic()还是运行时错误都能捕获常见的运行时 panic数组越界、nil 指针访问、类型断言失败、除零等4. 嵌套 panic 与 recover — 只有最内层的 recover 能捕获panic 只会被最近的最内层的recover 捕获外层的 recover 收到 nilpackage mainimportfmtfuncnestedPanic(){deferfunc(){fmt.Println(Outer recovery:, recover())// 这里会是 nil}()func(){deferfunc(){fmt.Println(Inner recovery:, recover())// 这里捕获 panic}()panic(Inner panic)}()}funcmain(){fmt.Println( nestedPanic example )nestedPanic()}执行结果nestedPanic exampleInner recovery: Inner panic Outer recovery:nil要点内层匿名函数的 recover 捕获了 “Inner panic”panic 在这里被恢复外层 nestedPanic 的 recover 收到nil因为 panic 已经被内层处理了原理panic 沿调用栈逐层 unwind遇到第一个 recover 就被捕获并停止 unwind这意味着一旦 panic 被 recover更高层的函数感知不到有 panic 发生过类似 try-catch内层 catch 捕获异常后外层 catch 不会再收到该异常5. recover 后程序继续运行panic 被 recover 捕获后程序从 recover 所在的 defer 函数返回处继续正常执行package mainimportfmtfunc safeDivide(a, b int)(result int){deferfunc(){ifr :recover();r!nil{fmt.Println(Recovered from panic:, r)result0}}()ifb0{panic(division by zero)}returna / b}func processArray(arr[]int){deferfunc(){ifr :recover();r!nil{fmt.Println(Recovered from array access panic)}}()value :arr[10]fmt.Println(Value at index 10:, value)}funcdemonstratePanic(){fmt.Println(Before panic)panic(Something went wrong!)fmt.Println(After panic)}funcnestedPanic(){deferfunc(){fmt.Println(Outer recovery:, recover())}()func(){deferfunc(){fmt.Println(Inner recovery:, recover())}()panic(Inner panic)}()}funcmain(){result1 :safeDivide(10,2)fmt.Println(Result:, result1)result2 :safeDivide(10,0)fmt.Println(Result:, result2)shortArr :[]int{1,2,3}processArray(shortArr)longArr :make([]int,15)fori :0;i15;i{longArr[i]i *10}processArray(longArr)func(){deferfunc(){ifr :recover();r!nil{fmt.Println(Caught panic from demonstratePanic:, r)}}()demonstratePanic()}()nestedPanic()// 所有 panic 都被 recover程序继续正常运行 fmt.Println(\nProgram continues normally)}执行结果Result:5Recovered from panic: division by zero Result:0Recovered from array access panic Value at index10:100Before panic Caught panic from demonstratePanic: Something went wrong!Inner recovery: Inner panic Outer recovery:nilProgram continues normally要点所有的 panic 都被 recover 捕获程序没有崩溃最后输出 “Program continues normally”证明 recover 后程序继续正常运行panic/recover 不是普通的错误处理机制Go 推荐用error处理可预期的错误panic/recover 适用于真正不可恢复的场景、库的内部防护、顶层兜底恢复知识点总结知识点关键概念panic 触发panic(msg)立即中断函数panic 后的代码不执行defer recoverrecover 只能在 defer 内调用捕获 panic 值并恢复执行recover 修改返回值利用命名返回值在 defer 中设置 panic 情况的返回值捕获运行时 panic数组越界、nil 指针等运行时错误也能被 recover 捕获嵌套 panic/recoverpanic 只被最内层 recover 捕获外层 recover 返回 nilrecover 后继续运行panic 被 recover 后程序从恢复点继续正常执行最佳实践可预期错误用error不可恢复错误用 panic/recover 兜底