Singleton 패턴과 DCL 에 대한 관계 설명

1. Singleton Pattern
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2. • , ( )

3. !
object: 0x40012a
~

4. !
object: 0x40012a
~

5. !
object: 0x40012a
~

6. N !
object: 0x40012a
~

7. object: 0x40012a
object: 0x40012a
object: 0x40012a
object: 0x40012a
N
.
.
.
.
.
.
N
!
?

8. ?
•
•

9. Singleton (1)
• private
•
static mInstance
• data instance

10. Singleton (2)
•
getInstance()
• Static

11. • s1, s2, s3 add()
3 ->
•
S1
add()
Data: 1
object
0x40012a

12. • s1, s2, s3 add()
3 ->
•
S1 S2
add() add()
Data: 1 Data: 2
object
0x40012a
object
0x40012a

13. • s1, s2, s3 add()
3 ->
•
S1 S2 S3
add() add() add()
Data: 1 Data: 2 Data: 3
object
0x40012a
object
0x40012a
object
0x40012a

14. Thread1 Thread2 Thread3
getInstance() getInstance() getInstance()

15. object: 0x400120
Thread1 Thread2 Thread3
getInstance() getInstance() getInstance()
nullptr !
!

16. object: 0x400120
Thread1
object: 0x400120
Thread2 Thread3
getInstance() getInstance() getInstance()
nullptr !
!
~

17. object: 0x400120
Thread1
object: 0x400120
Thread2
object: 0x400128
Thread3
getInstance() getInstance() getInstance()
nullptr !
!
~
nullptr?
! !
???

18. ?
~
Thread1
Thread2
Thread3
mInstance = nullptr
Thread1
mInstance = nullptr
Thread2
mInstance = nullptr
Thread3

19. ?
~
Thread1
Thread2
Thread3
mInstance = nullptr
Thread1
mInstance = nullptr
Thread2
mInstance = nullptr
Thread3

20. ?
~
Thread1
Thread2
Thread3
mInstance = nullptr
Thread1
mInstance = nullptr
Thread2
mInstance = nullptr
Thread3

21. ?
~
Thread1
Thread2
Thread3
mInstance = 0x400120
Thread1
mInstance = nullptr
Thread2
mInstance = nullptr
Thread3

22. ?
~
Thread1
Thread2
Thread3
mInstance = 0x400120
Thread1
mInstance = 0x400120
Thread2
mInstance = nullptr
Thread3

23. ?
~
Thread1
Thread3
mInstance = 0x400120
Thread1
mInstance = 0x400120
Thread2
mInstance = 0x400128
Thread3
Thread2

24. !
getInstance()+8 cmp mInstance, 0x0
getInstance()+12 jne getInstance()+20
getInstance()+16 mInstance = new Singleton()
getInstance()+20 ret
• if cmp Jmp instructure
.

25. !
getInstance()+8 cmp mInstance, 0x0
getInstance()+12 jne getInstance()+20
getInstance()+16 mInstance = new Singleton()
getInstance()+20 ret
Thread1
Thread3
Thread2
mInstance = nullptr

26. Thread1
getInstance()+8 cmp mInstance, 0x0
getInstance()+12 jne getInstance()+20
getInstance()+16 mInstance = new Singleton()
getInstance()+20 ret
Thread1(getInstance()+8)
Thread3
Thread2
mInstance = nullptr

27. jne instructure
getInstance()+8 cmp mInstance, 0x0
getInstance()+12 jne getInstance()+20
getInstance()+16 mInstance = new Singleton()
getInstance()+20 ret
Thread1(getInstance()+12)
Thread3
Thread2
mInstance = nullptr

28. mInstance nullptr
Thread3 cmp
getInstance()+8 cmp mInstance, 0x0
getInstance()+12 jne getInstance()+20
getInstance()+16 mInstance = new Singleton()
getInstance()+20 ret
Thread1(getInstance()+12)
Thread3(getInstance()+12)
Thread2
mInstance = nullptr

29. Thread3
Thread1
getInstance()+8 cmp mInstance, 0x0
getInstance()+12 jne getInstance()+20
getInstance()+16 mInstance = new Singleton()
getInstance()+20 ret
Thread1(getInstance()+16)
Thread2
mInstance = 0x400120
Thread3(getInstance()+12)

30. mInstance
Thread3
getInstance()+8 cmp mInstance, 0x0
getInstance()+12 jne getInstance()+20
getInstance()+16 mInstance = new Singleton()
getInstance()+20 ret
Thread1(getInstance()+20)
Thread2
Thread3(getInstance()+16)
mInstance = 0x400120
Thread1
mInstance = 0x400128
Thread3

31. • race condition
mutex thread
.
• ! Mutex !

32. DCL
(Double Checked Locking)
• Locking , if .
-> lock

33. DCL
(Double Checked Locking)
• instance , lock .

34. DCL
(Double Checked Locking)
• Locking thread-safe .
instance .

35. object: 0x40012a
object: 0x40012a
object: 0x40012a
object: 0x40012a
object: 0x40012a
Only One Object, Same Instance!
~