9.1.1 الگو Singleton

 1package main  
 2  
 3import (  
 4    "fmt"  
 5    "sync"    
 6    "time"
 7)  
 8  
 9type MyLogger struct {  
10}  
11  
12var (  
13    globalLogger *MyLogger  
14    mu           = &sync.Mutex{}  
15)  
16  
17func GetMyLoggerInstance(i int) *MyLogger {  
18    if globalLogger == nil {  
19       mu.Lock()  
20       defer mu.Unlock()  
21       if globalLogger == nil {  
22          fmt.Println("creating myLogger instance by", i)  
23          globalLogger = &MyLogger{}  
24       }  
25    } else {  
26       fmt.Println("myLogger instance already created.")  
27    }  
28  
29    return globalLogger  
30}  
31  
32func main() {  
33    for i := 1; i <= 5; i++ {  
34       go GetMyLoggerInstance(i)  
35    }  
36    time.Sleep(time.Second)  
37}

1$ go run main.go
2creating myLogger instance by 2
3myLogger instance already created.
4myLogger instance already created.
5myLogger instance already created.
6myLogger instance already created.

 1package main  
 2  
 3import (  
 4    "fmt"  
 5    "sync"
 6    "time"
 7)  
 8  
 9type MyLogger struct {  
10}  
11  
12var (  
13    globalLogger *MyLogger  
14    once         sync.Once  
15)  
16  
17func GetMyLoggerInstance(i int) *MyLogger {  
18    if globalLogger == nil {  
19       once.Do(  
20          func() {  
21             fmt.Println("creating myLogger instance by", i)  
22             globalLogger = &MyLogger{}  
23          })  
24    } else {  
25       fmt.Println("myLogger instance already created.")  
26    }  
27  
28    return globalLogger  
29}  
30  
31func main() {  
32    for i := 1; i <= 5; i++ {  
33       go GetMyLoggerInstance(i)  
34    }  
35    time.Sleep(time.Second)  
36}

1$ go run main.go
2creating myLogger instance by 4