焦虑：在循环中启动的goroutine中向已关闭的通道发送数据

目前golang学习网上已经有很多关于Golang的文章了，自己在初次阅读这些文章中，也见识到了很多学习思路；那么本文《焦虑：在循环中启动的goroutine中向已关闭的通道发送数据》，也希望能帮助到大家，如果阅读完后真的对你学习Golang有帮助，欢迎动动手指，评论留言并分享~

我正在尝试制作 grep 的并发版本。该程序遍历目录/子目录并将任何匹配的字符串返回给提供的模式。

一旦我拥有要搜索的所有文件（请参阅 searchpaths 函数），我将尝试同时运行文件搜索。最初我得到的是：

致命错误：所有 goroutine 都在休眠 - 死锁

直到我在 searchpaths 末尾添加 close(out) 为止，它现在返回到该位置：

panic：在 fooloop 中运行 go 例程时在关闭的通道上发送

我正在尝试实现类似的东西：

https://go.dev/blog/pipelines#fan-out-fan-in

我是否在错误的时间点关闭了通道？

package main

import (
    "fmt"
    "io/fs"
    "io/ioutil"
    "log"
    "os"
    "path/filepath"
    "strings"
    "sync"
)

type SearchResult struct {
    line       string
    lineNumber int
}

type Display struct {
    filePath string
    SearchResult
}

var wg sync.WaitGroup

func (d Display) PrettyPrint() {
    fmt.Printf("Line Number: %v\nFilePath: %v\nLine: %v\n\n", d.lineNumber, d.filePath, d.line)
}

func searchLine(pattern string, line string, lineNumber int) (SearchResult, bool) {
    if strings.Contains(line, pattern) {
        return SearchResult{lineNumber: lineNumber + 1, line: line}, true
    }
    return SearchResult{}, false
}

func splitIntoLines(file string) []string {
    lines := strings.Split(file, "\n")
    return lines
}

func fileFromPath(path string) string {
    fileContent, err := ioutil.ReadFile(path)

    if err != nil {
        log.Fatal(err)
    }

    return string(fileContent)
}

func getRecursiveFilePaths(inputDir string) []string {
    var paths []string
    err := filepath.Walk(inputDir, func(path string, info fs.FileInfo, err error) error {
        if err != nil {
            fmt.Printf("prevent panic by handling failure accessing a path %q: %v\n", path, err)
            return err
        }
        if !info.IsDir() {
            paths = append(paths, path)
        }
        return nil
    })
    if err != nil {
        fmt.Printf("Error walking the path %q: %v\n", inputDir, err)
    }
    return paths
}

func searchPaths(paths []string, pattern string) <-chan Display {
    out := make(chan Display)

    for _, path := range paths {
        wg.Add(1)
        go func() {
            defer wg.Done()
            for _, display := range searchFile(path, pattern) {
                out <- display
            }
        }()
    }
    close(out)
    return out
}

func searchFile(path string, pattern string) []Display {
    var out []Display
    input := fileFromPath(path)
    lines := splitIntoLines(input)
    for index, line := range lines {
        if searchResult, ok := searchLine(pattern, line, index); ok {
            out = append(out, Display{path, searchResult})
        }
    }
    return out
}

func main() {
    pattern := os.Args[1]
    dirPath := os.Args[2]

    paths := getRecursiveFilePaths(dirPath)

    out := searchPaths(paths, pattern)
    wg.Wait()
    for d := range out {
        d.PrettyPrint()
    }

}

正确答案

此代码的两个主要问题是

1. 只有在 wg.wait() 完成后才需要关闭通道。您可以在单独的 goroutine 中执行此操作，如下所示
2. 由于 searchpaths 函数中的 path var 作为 for 循环逻辑的一部分被重新分配多次，因此 直接在 goroutines 中使用该 var 不是一个好的做法，更好的方法是将其作为参数传递。

package main

import (
    "fmt"
    "io/fs"
    "io/ioutil"
    "log"
    "os"
    "path/filepath"
    "strings"
    "sync"
)

type SearchResult struct {
    line       string
    lineNumber int
}

type Display struct {
    filePath string
    SearchResult
}

var wg sync.WaitGroup

func (d Display) PrettyPrint() {
    fmt.Printf("Line Number: %v\nFilePath: %v\nLine: %v\n\n", d.lineNumber, d.filePath, d.line)
}

func searchLine(pattern string, line string, lineNumber int) (SearchResult, bool) {
    if strings.Contains(line, pattern) {
        return SearchResult{lineNumber: lineNumber + 1, line: line}, true
    }
    return SearchResult{}, false
}

func splitIntoLines(file string) []string {
    lines := strings.Split(file, "\n")
    return lines
}

func fileFromPath(path string) string {
    fileContent, err := ioutil.ReadFile(path)

    if err != nil {
        log.Fatal(err)
    }

    return string(fileContent)
}

func getRecursiveFilePaths(inputDir string) []string {
    var paths []string
    err := filepath.Walk(inputDir, func(path string, info fs.FileInfo, err error) error {
        if err != nil {
            fmt.Printf("prevent panic by handling failure accessing a path %q: %v\n", path, err)
            return err
        }
        if !info.IsDir() {
            paths = append(paths, path)
        }
        return nil
    })
    if err != nil {
        fmt.Printf("Error walking the path %q: %v\n", inputDir, err)
    }
    return paths
}

func searchPaths(paths []string, pattern string) chan Display {
    out := make(chan Display)
    for _, path := range paths {
        wg.Add(1)
        go func(p string, w *sync.WaitGroup) { // as path var is changing value in the loop, it's better to provide it as a argument in goroutine
            defer w.Done()
            for _, display := range searchFile(p, pattern) {
                out <- display
            }
        }(path, &wg)
    }
    return out
}

func searchFile(path string, pattern string) []Display {
    var out []Display
    input := fileFromPath(path)
    lines := splitIntoLines(input)
    for index, line := range lines {
        if searchResult, ok := searchLine(pattern, line, index); ok {
            out = append(out, Display{path, searchResult})
        }
    }
    return out
}

func main() {
    pattern := os.Args[1]
    dirPath := os.Args[2]

    paths := getRecursiveFilePaths(dirPath)

    out := searchPaths(paths, pattern)

    go func(){
        wg.Wait() // waiting before closing the channel
        close(out)
    }()
    
    count := 0
    for d := range out {
        fmt.Println(count)
        d.PrettyPrint()
        count += 1
    }

}

以上就是《焦虑：在循环中启动的goroutine中向已关闭的通道发送数据》的详细内容，更多关于的资料请关注golang学习网公众号！