Go语言可能会遇到的坑

时间 2021-08-13

标签 golang ide oop 测试调试 code 开发 string 栏目 Go 繁體版

原文原文链接

最近在用go开发项目的过程当中忽然发现一个坑，尤为是对于其它传统语言转来的人来讲一不注意就掉坑里了，话很少说，咱看代码：golang

1//writeToCSV
2func writeESDateToCSV(totalValues chan []string) {
3    f, err := os.Create("t_data_from_es.csv")
4    defer f.Close()
5    if err != nil {
6        panic(err)
7    }
8
9    w := csv.NewWriter(f)
10    w.Write(columns)
11
12    for {
13        select {
14        case row := <- totalValues:
15            //fmt.Printf("Write Count:%d log:%s\n",i, row)
16            w.Write(row)
17        case <- isSendEnd:
18            if len(totalValues) == 0 {
19                fmt.Println("------------------Write End-----------------")
20                break
21            }
22        }
23    }
24
25    w.Flush()
26    fmt.Println("-------------------------处理完毕-------------------------")
27    isWriteEnd <- true
28}ide

当数据发送完毕，即isSendEnd不阻塞，且totalValues里没数据时，跳出for循环，这里用了break。可是调试的时候发现，程序阻塞在了14行，即两个channel都阻塞了。而后才惊觉这里break不是这么玩，而后写了个测试方法测试一下：oop

package main

import (
    "time"
    "fmt"
)

func main() {
    i := 0
    for {
        select {
        case <-time.After(time.Second * time.Duration(2)):
            i++
            if i == 5{
                fmt.Println("break now")
                break
            }
            fmt.Println("inside the select: ")
        }
        fmt.Println("inside the for: ")
    }

    fmt.Println("outside the for: ")
}测试

运行输出以下结果，break now以后仍是会继续无限循环，不会跳出for循环，只是跳出了一次select调试

inside the select:
inside the for:
inside the select:
inside the for:
inside the select:
inside the for:
inside the select:
inside the for:
break now
inside the for:
inside the select:
inside the for:
inside the select:
inside the for:
inside the select:
inside the for: code

若要break出来，这里须要加一个标签，使用goto，或者break 到具体的位置。开发

解决方法一：string

使用golang中break的特性，在外层for加一个标签：it

package main

import (
    "time"
    "fmt"
)

func main() {
    i := 0

    endLoop:
    for {
        select {
        case <-time.After(time.Second * time.Duration(2)):
            i++
            if i == 5{
                fmt.Println("break now")
                break endLoop
            }
            fmt.Println("inside the select: ")
        }
        fmt.Println("inside the for: ")
    }

    fmt.Println("outside the for: ")
}io

解决方法二：

使用goto直接跳出循环：

package main

import (
    "time"
    "fmt"
)

func main() {
    i := 0
    for {
        select {
        case <-time.After(time.Second * time.Duration(2)):
            i++
            if i == 5{
                fmt.Println("break now")
                goto endLoop
            }
            fmt.Println("inside the select: ")
        }
        fmt.Println("inside the for: ")
    }
    endLoop:
    fmt.Println("outside the for: ")
}

两程序运行输出以下：

inside the select:
inside the for:
inside the select:
inside the for:
inside the select:
inside the for:
inside the select:
inside the for:
break now
outside the for:

Process finished with exit code 0

综上能够得出：go语言的switch-case和select-case都是不须要break的，可是加上break也只是跳出本次switch或select，并不会跳出for循环。