进行全局变量初始化

Question

Issue on loading the configuration on file scope global variable.

The config setting and and loading config values inside main method

func main() {

    if err := config.LoadConfig(); err != nil {
        logrus.Info("Unable to read config : ")
        os.Exit(-1)
    }

    fmt.Println(config.GetConfig().Value) // print the correct value

    service.Test() // prints 0  

}

my config setting. config.go

var appConfig AppConfig

func LoadConfig() error {
  // loads config
  appConfig = .... 
}

func GetConfig() AppConfig {
    return appConfig
}

I have another service file with global variable defined inside service.go

   var x = config.GetConfig().Value

    func Test(){
      fmt.Println(x)
    }

Question:

Why my global variable x inside service.go is not initialized ?

Thanks

Answer 1

Per the Go specification, the order of execution is as follows:

Package initialization—variable initialization and the invocation of init functions—happens in a single goroutine, sequentially, one package at a time. An init function may launch other goroutines, which can run concurrently with the initialization code. However, initialization always sequences the init functions: it will not invoke the next one until the previous one has returned.

Program execution begins by initializing the main package and then invoking the function main. When that function invocation returns, the program exits. It does not wait for other (non-main) goroutines to complete.

Meaning the order is roughly:

1. Global variables get initialized
2. init() functions run
3. main() runs

So your global initialization is happening before main() has a chance to load your configuration.