type channelPool struct {
mu sync.RWMutex
conns chan *idleConn
factory func() (interface{}, error)
close func(interface{}) error
ping func(interface{}) error
idleTimeout, waitTimeOut time.Duration
maxActive int
openingConns int
connReqs []chan connReq
}
里面的conns为啥要使用chan *idleConn，直接使用chan idleConn不可以吗？