Singleton实例继续在Go中创建新实例

Question

I am using redis to store sessions for my Go simple web app. For this, I only want a single session to access the redis connection at a time. I searched up on implementing singleton objects in Go and followed. This is the code I'm currently implementing:

Redis connection:

package Datab

import (
    "github.com/gomodule/redigo/redis"
)

type cache struct {
    Conn redis.Conn
}

var singleCache *cache = nil

func GetSessionCache() *cache {

    if singleCache == nil {

        singleCache := &cache{}
        singleCache.Conn, _ = redis.DialURL("redis://localhost")
        // ^ SINGLECACHE IS NOT NIL HERE.

    }
    return singleCache
    // ^ SAYS THIS IS NIL!

}

---

Redis Implementation:

package Handler

import (
    Datab "videodoox/DB" // this file contains the redis connection implementation
)

connStru := *Datab.GetSessionCache()
cache := connStru.Conn

connStru2 := *Datab.GetSessionCache()
cache2: = connStru.Conn
// ^ THIS CONNECTION HERE IS A COMPLETELY NEW INSTANCE.

---

Everytime I get the connection, the redis connection file creates a new instance of the connection. How do I create a new connection once and just return that connection everytime? Thanks!

Answer 1

Comments to the initial question solve the issue, but just to provide a complete solution your code can look like:

package Datab

import (
    "sync"

    "github.com/gomodule/redigo/redis"
)

type cache struct {
    Conn redis.Conn
}

var singleCache *cache
var initOnce sync.Once

func GetSessionCache() *cache {
    initOnce.Do(func() {
        singleCache := &cache{}
        singleCache.Conn, _ = redis.DialURL("redis://localhost")
    })

    return singleCache
}

Just a couple of extra notes:

• No need to specify nil as an initial value of pointers, zero value for them is nil by default (var singleCache *cache vs var singleCache *cache = nil).
• You should handle potential error returned by redis.DialURL and not just skip it with _.