Singleton 패턴 (김진영 - EVA, 소마에 10기)

•

1 like•419 views

The Singleton pattern ensures that only one instance of a class is created and provides a global access point to that instance. It describes how to implement the concept of a singleton class by creating a private constructor, a static method that returns the instance, and a static property that holds the single instance of the class. The document discusses issues that can arise with thread safety when multiple threads simultaneously try to access the singleton instance and provides solutions like using mutex locking to ensure only one thread initializes the instance.

Technology

object: 0x40012a
object: 0x40012a
object: 0x40012a
object: 0x40012a
N
.
.
.
.
.
.
N
!
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Singleton (1)
• private

•
static mInstance

• data instance

• s1, s2, s3 add()
3 ->

•
S1
add()
Data: 1
object
0x40012a

• s1, s2, s3 add()
3 ->

•
S1 S2
add() add()
Data: 1 Data: 2
object
0x40012a
object
0x40012a

• s1, s2, s3 add()
3 ->

•
S1 S2 S3
add() add() add()
Data: 1 Data: 2 Data: 3
object
0x40012a
object
0x40012a
object
0x40012a

Thread1 Thread2 Thread3
getInstance() getInstance() getInstance()

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

• race condition
mutex thread
.

• ! Mutex !

DCL
(Double Checked Locking)
• Locking , if .

-> lock

DCL
(Double Checked Locking)
• instance , lock .

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

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

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Singleton 패턴 (김진영 - EVA, 소마에 10기)

1. Singleton Pattern sdk159147@gmail.com

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! ~

Singleton 패턴 (김진영 - EVA, 소마에 10기)

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