背景

很多时候我们希望程序可以单例运行

怎么去做

• 监听端口形式的http或tcp

  此方式需要占用系统端口，有“洁癖”的小伙伴可能不太能接受

• 用unix形式即sock方式监听

实现

package single

import (
    "bytes"
    "crypto/md5"
    "encoding/hex"
    "errors"
    "net"
    "os"
    "os/exec"
    "os/user"
    "path/filepath"
    "runtime"
    "strings"
)

var socketFile string

// Start start single
func Start(socketFile string) (started bool) {
    c, _ := net.Dial("unix", socketFile)
    if c != nil {
        return true
    }
    go func() {
        os.Remove(socketFile)
        l, err := net.Listen("unix", socketFile)
        if err != nil {
            panic(err)
        }
        defer l.Close()

        for {
            conn, err := l.Accept()
            if err != nil {

            } else {
                conn.Close()
            }
        }
    }()
    return false
}

// StartAuto auto start
func StartAuto() bool {
    h := md5.New()
    execName := os.Args[0]
    dir := filepath.Dir(execName)
    dirAbs, err := filepath.Abs(dir)
    if err == nil && dirAbs != dir {
        execName = filepath.Join(dirAbs, execName)
    }
    h.Write([]byte(execName))
    filename := hex.EncodeToString(h.Sum(nil))

        // 这里没有使用临时目录，考虑到临时目录可能随时会被清理
    p, e := home()
    if e != nil {
        p = "./"
    }
    filepath := filepath.Join(p, "."+filepath.Base(execName)+"-"+filename+".sock")
    return Start(filepath)
}

func home() (string, error) {
    user, err := user.Current()
    if nil == err {
        return user.HomeDir, nil
    }

    // cross compile support

    if "windows" == runtime.GOOS {
        return homeWindows()
    }

    // Unix-like system, so just assume Unix
    return homeUnix()
}

func homeUnix() (string, error) {
    // First prefer the HOME environmental variable
    if home := os.Getenv("HOME"); home != "" {
        return home, nil
    }

    // If that fails, try the shell
    var stdout bytes.Buffer
    cmd := exec.Command("sh", "-c", "eval echo ~$USER")
    cmd.Stdout = &stdout
    if err := cmd.Run(); err != nil {
        return "", err
    }

    result := strings.TrimSpace(stdout.String())
    if result == "" {
        return "", errors.New("blank output when reading home directory")
    }

    return result, nil
}

func homeWindows() (string, error) {
    drive := os.Getenv("HOMEDRIVE")
    path := os.Getenv("HOMEPATH")
    home := drive + path
    if drive == "" || path == "" {
        home = os.Getenv("USERPROFILE")
    }
    if home == "" {
        return "", errors.New("HOMEDRIVE, HOMEPATH, and USERPROFILE are blank")
    }

    return home, nil
}

用法如下

package main

import (
    "fmt"
    "goutils/single"
)

func main() {
    // 自动使用sock文件
    // started := single.StartAuto()

    // 指定sock文件
    started := single.Start("./1.sock")
    if started {
        fmt.Println("已经启动了一个实例")
    } else {
        fmt.Println("第一次运行")
        select {}
    }
}

源码

• github
• gitee