golang--redigo中连接池的使用

川长思鸟来 2021-12-07 11:57 533阅读 0赞

# redigo连接池的使用 #

### 文章目录 ###

*  redigo连接池的使用
 *   *  前言
     *  conn
     *  连接池
     *   *  例程

--------------------

## 前言 ##

最近使用redigo的时候遇到了并发问题，于是想起了redigo并发是否存在安全性的问题，查了下源码，发现可以用连接池解决，简单介绍一下。

## conn ##

redigo实现了不止一种的Conn对象，一般初次使用，会用redis.Dial()获取一条连接对象。  
它是在conn.go中定义的对象。

// conn is the low-level implementation of Conn
    type conn struct {
        
    	// Shared
    	mu      sync.Mutex
    	pending int
    	err     error
    	conn    net.Conn
    
    	// Read
    	readTimeout time.Duration
    	br          *bufio.Reader
    
    	// Write
    	writeTimeout time.Duration
    	bw           *bufio.Writer
    
    	// Scratch space for formatting argument length.
    	// '*' or '$', length, "\r\n"
    	lenScratch [32]byte
    
    	// Scratch space for formatting integers and floats.
    	numScratch [40]byte
    }

它实际上是一种低水平的实现，在遇到多协程需要并发操作时是不能用它的 :

![\[外链图片转存失败(img-nrxuA0pv-1563279188074)(./1563275388184.png)\]][img-nrxuA0pv-1563279188074_._1563275388184.png]

## 连接池 ##

连接池其实就是一种线程池模型，预先开辟并申请一定数量的资源放在池子中，用的时候取一条出来，用完在放回去。  
不清楚线程池的可以看看我以前写的[c++实现的线程池文章][c]了解下。

接着看看pool，pool的Get()方法可以获取一条Conn对象，它是activeConn对象，不同于上面的conn，它也实现了Conn接口。

// NewPool creates a new pool.
    //
    // Deprecated: Initialize the Pool directory as shown in the example.
    func NewPool(newFn func() (Conn, error), maxIdle int) *Pool {
        
    	return &Pool{
        Dial: newFn, MaxIdle: maxIdle}
    }
    
    // Get gets a connection. The application must close the returned connection.
    // This method always returns a valid connection so that applications can defer
    // error handling to the first use of the connection. If there is an error
    // getting an underlying connection, then the connection Err, Do, Send, Flush
    // and Receive methods return that error.
    func (p *Pool) Get() Conn {
        
    	pc, err := p.get(nil)
    	if err != nil {
        
    		return errorConn{
        err}
    	}
    	return &activeConn{
        p: p, pc: pc}
    }
    
    // Close releases the resources used by the pool.
    func (p *Pool) Close() error {
        
    	....

type activeConn struct {
        
    	p     *Pool
    	pc    *poolConn
    	state int
    }

// Conn represents a connection to a Redis server.
    type Conn interface {
        
    	// Close closes the connection.
    	Close() error
    
    	// Err returns a non-nil value when the connection is not usable.
    	Err() error
    
    	// Do sends a command to the server and returns the received reply.
    	Do(commandName string, args ...interface{
        }) (reply interface{
        }, err error)
    
    	// Send writes the command to the client's output buffer.
    	Send(commandName string, args ...interface{
        }) error
    
    	// Flush flushes the output buffer to the Redis server.
    	Flush() error
    
    	// Receive receives a single reply from the Redis server
    	Receive() (reply interface{
        }, err error)
    }

### 例程 ###

3个协程同时进行redis的ping操作，连接池中有最大活跃数2条，最大闲置数1条，  
结果会有一个协程在进行Do方法时`connection pool exhausted` 返回连接池资源耗尽错误， 注意它不是在Get()的时候报错，而是会在使用这个Conn对象的时候返回错误。

另外pool的Coon由两种状态Idle和Active，使用中的连接是Active状态超时(IdleTimeout)后变为Idle状态，idle状态的连接数目最多为MaxIdle条，active状态的连接数最多为MaxActive条。

package main
    
    import(
    	"fmt"
    	"time"
    	"./redigo/redis"
    )
    
    func TestPing(){
        
    	conn := redisPool.Get()
    	res, _ := conn.Do("ping")
    	fmt.Println(res.(string))
    	conn.Close()
    }
    
    func newRedisPool(addr string) *redis.Pool {
        
    	return &redis.Pool{
        
    		MaxIdle: 1,
    		MaxActive: 2,
    		IdleTimeout: 6 * time.Second,
    		// Dial or DialContext must be set. When both are set, DialContext takes precedence over Dial.
    		Dial: func () (redis.Conn, error) {
         return redis.Dial("tcp", addr) },
    	}
    }
    
    var (
    	redisPool *redis.Pool
    	redisServer = "127.0.0.1:6379"
    )
    
    func TestPoolMaxIdle() {
        
    
    	go func(){
        
    		fmt.Println("go---1---")
    		conn := redisPool.Get()
    		fmt.Println("go---1---: Get Conn")
    		defer conn.Close()
    
    		res, err := conn.Do("ping")
    		if err != nil {
        
    			fmt.Println("go---1---error:", err)
    			return
    		}
    		fmt.Println("go---1---:", res.(string))
    
    		time.Sleep(3*time.Second)
    	}()
    
    	go func(){
        
    		fmt.Println("go---2---")
    		conn := redisPool.Get()
    		fmt.Println("go---2---: Get Conn")
    		defer conn.Close()
    
    		res, err := conn.Do("ping")
    		if err != nil {
        
    			fmt.Println("go---2---error:", err)
    			return
    		}
    		fmt.Println("go---2---:", res.(string))
    
    		time.Sleep(3*time.Second)
    	}()
    
    	go func(){
        
    		fmt.Println("go---3---")
    		conn := redisPool.Get()
    		fmt.Println("go---3---: Get Conn")
    		defer conn.Close()
    
    		time.Sleep(5*time.Second)
    		res, err := conn.Do("ping")
    		if err != nil {
        
    			fmt.Println("go---3---error:", err)
    			return
    		}
    		fmt.Println("go---3---:", res.(string))
    
    		time.Sleep(3*time.Second)
    	}()
    }
    
    func main()  {
        
    	redisPool = newRedisPool(redisServer)
    	fmt.Println("-------------PoolStats------------")
    	fmt.Println("Active/Idle:", redisPool.ActiveCount(), ":", redisPool.IdleCount())
    
    	fmt.Println("-------------TestPing------------")
    	TestPing()
    
    	fmt.Println("-------------PoolStats------------")
    	fmt.Println("Active/Idle:", redisPool.ActiveCount(), ":", redisPool.IdleCount())
    
    	time.Sleep(8*time.Second)
    
    	fmt.Println("-------------PoolStats------------")
    	fmt.Println("Active/Idle:", redisPool.ActiveCount(), ":", redisPool.IdleCount())
    
    	fmt.Println("-------------TestPoolMaxIdle------------")
    	TestPoolMaxIdle()
    
    	time.Sleep(1*time.Second)
    	fmt.Println("-------------PoolStats------------")
    	fmt.Println("Active/Idle:", redisPool.ActiveCount(), ":", redisPool.IdleCount())
    
    	time.Sleep(20*time.Second)
    
    	fmt.Println("-------------PoolStats------------")
    	fmt.Println("Active/Idle:", redisPool.ActiveCount(), ":", redisPool.IdleCount())
    }

![\[外链图片转存失败(img-e9krZj69-1563279188080)(./1563279050566.png)\]][img-e9krZj69-1563279188080_._1563279050566.png]

[img-nrxuA0pv-1563279188074_._1563275388184.png]: /images/20211207/dc65d0eca5a849878d77b7de0bca8c15.png
[c]: https://blog.csdn.net/qq_17308321/article/details/84501822
[img-e9krZj69-1563279188080_._1563279050566.png]: /images/20211207/db70e80efc154119827e389451b472cd.png