以下是我最终编写的代码，在Windows和MacOS上都是安全的：

var fs = require('fs')

module.exports = class SingleInstance {
    constructor(){
        this.appName = app.name.split(' ').join('-').toLowerCase()

        this.tmpPath = app.getPath('temp') + '\\' + this.appName + '\\'

        if (process.platform === 'darwin') this.tmpPath  = this.tmpPath.split('\\').join('//')

        if (!fs.existsSync(this.tmpPath)) fs.mkdirSync(this.tmpPath)

        this.lockFilePath = this.tmpPath + 'lock.txt'

        if (this.isSecondInstance()){
            process.exit()
        } else {
            this.updateLockFile()
        }
    }

    updateLockFile(){
        fs.writeFileSync(this.lockFilePath, process.pid.toString())
    }
    
    isSecondInstance(){
        try {
            var pid = fs.readFileSync(this.lockFilePath).toString()

            try {
                var isAlreadyRunning = process.kill(pid, 0)
                //app is the second instance. terminate.
                return true
            } catch(err) { }
        } catch(err) { }
    }
}