What are the application scenarios of singleton pattern in Golang?

Golang is an open source statically typed programming language that is efficient, powerful and concise. In Golang, the singleton pattern is a commonly used design pattern to ensure that a class has only one instance and provides a global access point. The singleton pattern can play a role in many scenarios. The following will introduce some scenarios suitable for applying the singleton pattern in Golang, and attach specific code examples.

1. Database Connection Pool
   In highly concurrent web applications, frequently creating and destroying database connections is very resource intensive. By using the singleton mode to manage the database connection pool, you can effectively reduce the number of connection creation and destruction times and improve system performance. The following is a simple database connection pool example:

package database

import (
    "database/sql"
    "sync"
    _ "github.com/go-sql-driver/mysql"
)

var db *sql.DB
var once sync.Once

func GetDB() *sql.DB {
    once.Do(func() {
        var err error
        db, err = sql.Open("mysql", "username:password@tcp(127.0.0.1:3306)/dbname")
        if err != nil {
            panic(err)
        }
    })
    return db
}

2. Configuration file reading
   In projects, it is usually necessary to read configuration files to initialize system parameters. In this case, You can use the singleton pattern to ensure that the configuration object is instantiated only once. The following is a simple configuration file reading example:

package config

import (
    "github.com/spf13/viper"
    "sync"
)

type Config struct {
    DatabaseUsername string
    DatabasePassword string
}

var instance *Config
var once sync.Once

func GetConfig() *Config {
    once.Do(func() {
        viper.SetConfigFile("config.yaml")
        viper.ReadInConfig()

        instance = &Config{
            DatabaseUsername: viper.GetString("database.username"),
            DatabasePassword: viper.GetString("database.password"),
        }
    })
    return instance
}

3. Logger
   Logging in an application is a common behavior, and the log can be ensured through the singleton pattern A unique instance of a logger to avoid duplicate logger creation and improve logging efficiency. The following is a simple logger example:

package logger

import (
    "log"
    "sync"
)

type Logger struct {
}

var instance *Logger
var once sync.Once

func GetLogger() *Logger {
    once.Do(func() {
        instance = &Logger{}
    })
    return instance
}

func (l *Logger) Log(message string) {
    log.Println(message)
}

The above are some scenarios and specific code examples suitable for applying the singleton mode in Golang. You can flexibly apply it according to project needs in actual development. Singleton mode improves code reusability and performance.

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