只適用於單線程環境
package main
import "fmt"
type Single struct {
}
var single *Single
func GetSingle() *Single {
if single == nil {
single = &Single{}
}
return single
}
func main() {
fmt.Printf("%p\n", GetSingle())
fmt.Printf("%p\n", GetSingle())
fmt.Printf("%p\n", GetSingle())
}
支持並發版本
package main
import (
"fmt"
"sync"
"time"
)
type Single2 struct {
}
var single2 *Single2
var lock *sync.Mutex = &sync.Mutex{}
func GetSingle2() *Single2 {
lock.Lock()
defer lock.Unlock()
if single2 == nil {
single2 = &Single2{}
}
return single2
}
func main() {
go fmt.Printf("%p\n", GetSingle2())
go fmt.Printf("%p\n", GetSingle2())
go fmt.Printf("%p\n", GetSingle2())
time.Sleep(time.Second)
fmt.Println("done")
}
優化並發版本
package main
import (
"fmt"
"sync"
"time"
)
type Single2 struct {
}
var single2 *Single2
var lock *sync.Mutex = &sync.Mutex{}
func GetSingle2() *Single2 {
if single2 == nil {
lock.Lock()
defer lock.Unlock()
if single2 == nil {
single2 = &Single2{}
}
}
return single2
}
func main() {
go fmt.Printf("%p\n", GetSingle2())
go fmt.Printf("%p\n", GetSingle2())
go fmt.Printf("%p\n", GetSingle2())
time.Sleep(time.Second)
fmt.Println("done")
}
sync.Once版本
package main
import (
"fmt"
"sync"
"time"
)
type Single3 struct {
}
var once sync.Once
var single3 *Single3
func GetSingle3() *Single3 {
once.Do(func() {
single3 = &Single3{}
})
return single3
}
func main() {
go fmt.Printf("%p\n", GetSingle3())
go fmt.Printf("%p\n", GetSingle3())
go fmt.Printf("%p\n", GetSingle3())
time.Sleep(time.Second)
fmt.Println("done")
}
