如何在Go語言中正確關(guān)閉多個(gè)Goroutine共享的數(shù)據(jù)庫連接？

package main  import (     "fmt"     "sync"     "time"      "database/sql"     _ "github.com/go-sql-driver/mysql" // 替換成你的數(shù)據(jù)庫驅(qū)動(dòng) )  type dbConn struct {     conn *sql.DB     wg   *sync.WaitGroup }  func openDb() (*dbConn, error) {     db, err := sql.Open("mysql", "user:password@tcp(127.0.0.1:3306)/database") // 替換成你的數(shù)據(jù)庫連接字符串     if err != nil {         return nil, err     }     return &dbConn{conn: db, wg: &sync.WaitGroup{}}, nil }  func (dc *dbConn) close() error {     dc.wg.Wait() // 等待所有 Goroutine 完成     return dc.conn.Close() }  func querydb(dc *dbConn, i int) {     defer dc.wg.Done()     dc.wg.Add(1) // 計(jì)數(shù)器加1     // ... 數(shù)據(jù)庫操作 ...     time.Sleep(time.Second) // 模擬數(shù)據(jù)庫操作耗時(shí)     fmt.Printf("Goroutine %d finishedn", i) }  func main() {     dc, err := openDb()     if err != nil {         fmt.Println("Error opening database:", err)         return     }     defer dc.close() // 確保最后關(guān)閉連接      for i := 0; i < 5; i++ {         go querydb(dc, i)     }      fmt.Println("Main goroutine waiting...")     //time.Sleep(3*time.Second) // 可選：等待Goroutine完成，如果數(shù)據(jù)庫操作時(shí)間不確定，則需要其他機(jī)制等待 }