Go创建Grpc链接池实现过程详解

func main(){
	//... some code
	// 链接grpc服务
	conn , err := grpc.Dial(":8000",grpc.WithInsecure)
	if err != nil {
		//...log
	}
	defer conn.Close()
	//...some code

type Pool interface {
	// 获取一个新的连接 ， 当关闭连接的时候，会将该连接放入到池子中
   Get() (Conn, error)
	// 关闭连接池，自然连接池子中的连接也不再可用
   Close() error
	//[#本文来源：janrs.com#]
   Status() string
}

func New(address string, option Options) (Pool, error) {
   if address == "" {
      return nil, errors.New("invalid address settings")
   }
   if option.Dial == nil {
      return nil, errors.New("invalid dial settings")
   }
   if option.MaxIdle <= 0 || option.MaxActive <= 0 || option.MaxIdle > option.MaxActive {
      return nil, errors.New("invalid maximum settings")
   }
   if option.MaxConcurrentStreams <= 0 {
      return nil, errors.New("invalid maximun settings")
   }
   p := &pool{
      index:   0,
      current: int32(option.MaxIdle),
      ref:     0,
      opt:     option,
      conns:   make([]*conn, option.MaxActive),
      address: address,
      closed:  0,
   }
   for i := 0; i < p.opt.MaxIdle; i++ {
      c, err := p.opt.Dial(address)
      if err != nil {
         p.Close()
         return nil, fmt.Errorf("dial is not able to fill the pool: %s", err)
      }
      p.conns[i] = p.wrapConn(c, false)
   }
   log.Printf("new pool success: %v\n", p.Status())
   return p, nil
}

// 关闭连接池
func (p *pool) Close() error {
   atomic.StoreInt32(&p.closed, 1)
   atomic.StoreUint32(&p.index, 0)
   atomic.StoreInt32(&p.current, 0)
   atomic.StoreInt32(&p.ref, 0)
   p.deleteFrom(0)
   log.Printf("[janrs.com]close pool success: %v\n", p.Status())
   return nil
}

// 清除从 指定位置开始到 MaxActive 之间的连接
func (p *pool) deleteFrom(begin int) {
   for i := begin; i < p.opt.MaxActive; i++ {
      p.reset(i)
   }
}

// 清除具体的连接
func (p *pool) reset(index int) {
   conn := p.conns[index]
   if conn == nil {
      return
   }
   conn.reset()
   p.conns[index] = nil
}

func (c *conn) reset() error {
   cc := c.cc
   c.cc = nil
   c.once = false
   // 本文博客来源：janrs.com
   if cc != nil {
      return cc.Close()
   }
   return nil
}
func (c *conn) Close() error {
   c.pool.decrRef()
   if c.once {
      return c.reset()
   }
   return nil
}

func (p *pool) Get() (Conn, error) {
   // the first selected from the created connections
   nextRef := p.incrRef()
   p.RLock()
   current := atomic.LoadInt32(&p.current)
   p.RUnlock()
   if current == 0 {
      return nil, ErrClosed
   }
   if nextRef <= current*int32(p.opt.MaxConcurrentStreams) {
      next := atomic.AddUint32(&p.index, 1) % uint32(current)
      return p.conns[next], nil
   }
   // 本文博客来源：janrs.com
   // the number connection of pool is reach to max active
   if current == int32(p.opt.MaxActive) {
      // the second if reuse is true, select from pool's connections
      if p.opt.Reuse {
         next := atomic.AddUint32(&p.index, 1) % uint32(current)
         return p.conns[next], nil
      }
      // the third create one-time connection
      c, err := p.opt.Dial(p.address)
      return p.wrapConn(c, true), err
   }
   // the fourth create new connections given back to pool
   p.Lock()
   current = atomic.LoadInt32(&p.current)
   if current < int32(p.opt.MaxActive) && nextRef > current*int32(p.opt.MaxConcurrentStreams) {
      // 2 times the incremental or the remain incremental  ##janrs.com
      increment := current
      if current+increment > int32(p.opt.MaxActive) {
         increment = int32(p.opt.MaxActive) - current
      }
      var i int32
      var err error
      for i = 0; i < increment; i++ {
         c, er := p.opt.Dial(p.address)
         if er != nil {
            err = er
            break
         }
         p.reset(int(current + i))
         p.conns[current+i] = p.wrapConn(c, false)
      }
	  // 本文博客来源：janrs.com
      current += i
      log.Printf("#janrs.com#grow pool: %d ---> %d, increment: %d, maxActive: %d\n",
         p.current, current, increment, p.opt.MaxActive)
      atomic.StoreInt32(&p.current, current)
      if err != nil {
         p.Unlock()
         return nil, err
      }
   }
   p.Unlock()
   next := atomic.AddUint32(&p.index, 1) % uint32(current)
   return p.conns[next], nil
}