Swift - ARC와 메모리 관리

ARC and
Memory Management
in Swift
Swift 에서의 Automatic Reference Counting 과 메모리 관리
@daheenallwhite!1

메모리 관리 Reference
Counting
in Swift
- Strong
- Weak
- Unowned
- Closure
Contents
2

!3
메모리 관리의 필요성
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한정된 자원
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Process
Program
Thread
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!4
Swift 에서 메모리 사용
Code
Static
Heap
Stack Value Type
Reference Type

!5
Reference Counting
필요한 동안만 메모리에 있도록 하자!
💡
해당 instance를 참조하면 count +1
해당 instance를 필요로 하는 애들의 숫자를 세자!

6
메모리에서 class instance 생명 주기
1. Allocation : 인스턴스를 위한 메모리 공간 찾기 🔍
2. Initialization : init()
3. 인스턴스 사용
4. Deinitialization : deinit() (메모리 회수 직전)
5. Deallocation

!7
Reference Counting 적용한 코드
class Point {
var x, y: Int
init(x: Int, y: Int) {
self.x = x
self.y = y
}
}
let point1 = Point(x: 0, y: 0)
let point2 = point1
// use point1
// use point2
작성한 코드
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
Swift 컴파일러가 ARC 적용하여 생성한 코드

!8
Reference Counting - Runtime
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2

!9
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2 refCount: 1
x: 0
y: 0

!10
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2 refCount: 1
x: 0
y: 0

!11
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2 refCount: 2
x: 0
y: 0

!12
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2 refCount: 1
x: 0
y: 0

!13
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2 refCount: 1
x: 0
y: 0

!14
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2 refCount: 0
x: 0
y: 0

!15
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack
point1
point2 refCount: 0
x: 0
y: 0

!16
class Point {
var refCount: Int
var x, y: Int
self.x = x
self.y = y
}
}
let point2 = point1
retain(point2)
// use point1
release(point1)
// use point2
release(point2)
HeapStack

!17
MRC / ARC
Manual Automatic
Apple release note - Transitioning to ARC

Strong Reference
Class TabletClass User
class User {
let name: String
var tablet: Tablet?
init(name: String) {
self.name = name
print("생성: User (self.name)")
}
deinit {
print("소멸: User (self.name)")
}
}
class Tablet {
let model: String
var owner: User?
init(model: String) {
self.model = model
print("생성: Phone (self.model)")
}
deinit {
print("소멸: Phone (self.model)")
}
}
!18
🧒

!19
Strong Reference
var iPadProvar dana
<User Instance>
name: “Dana”
tablet: <Tablet Instance>
<Tablet Instance>
model: “iPad Pro”
owner: <User Instance>
var dana: User? = User(name: "Dana")
var iPadPro: Tablet? = Tablet(model: "iPad Pro")

!20
Strong Reference
var iPadProvar 흰
<Tablet Instance>
// 새로 샀다!!
dana!.tablet = iPadPro
iPadPro!.owner = dana
var dana
<User Instance>
name: “Dana”

!21
Strong Reference Cycle
var iPadProvar 흰
<Tablet Instance>
!21
strong strong
strong
strong
var dana
<User Instance>
name: “Dana”

!22
var iPadProvar 흰
<Tablet Instance>
!22
strong strong
strong
strong
// 박살남.. 😇 😭
iPadPro = nil
var dana
<User Instance>
name: “Dana”

!23
var iPadProvar 흰
<Tablet Instance>
!23
strong
strong
strong
var dana
<User Instance>
name: “Dana”
// 박살남.. 😇 😭
iPadPro = nil

!24
var iPadProvar 흰
<Tablet Instance>
!24
strong
strong
strong
// 박살남.. 😇 😭
iPadPro = nil
// 집 나감 🤬
dana = nil
var dana
<User Instance>
name: “Dana”

!25
var iPadProvar 흰
<Tablet Instance>
!25
strong
strong
var dana
<User Instance>
name: “Dana”
// 박살남.. 😇 😭
iPadPro = nil
// 집 나감 🤬
dana = nil

!26
var iPadProvar 흰
<Tablet Instance>
!26
strong
strong
// 박살남.. 😇 😭
iPadPro = nil
// 집 나감 🤬
흰 = nil
var dana
<User Instance>
name: “Dana”
// 박살남.. 😇 😭
iPadPro = nil
// 집 나감 🤬
dana = nil

!27
Strong Reference Cycle 해결
원인
Reference count 를 0으로 만들지 못하게 함
두 인스턴스의 상대적인 수명을 알 수 없음
해결
Strong Reference 일 때만 reference count를 세자!
상대적인 수명에 대한 정보를 미리 알려주자!

해결 방법 - weak & unowned references
weak unowned
수명>
weak
<=
unowned
해당 instance에서 참조하는 instance가
더 적은 시간동안 메모리에 있는 경우
해당 instance에서 참조하는 instance가
더 오래 혹은 같은 시간동안
메모리에 있어야 하는 경우
참조하는 속성 값 == nil
인스턴스가 있을수도/없을수도
Optional
상대 인스턴스에 의존관계인 경우
항상 있어야 할 때
Non-optional

해결 - Weak Reference
Class TabletClass User
class User {
let name: String
weak var tablet: Tablet?
self.name = name
}
deinit {
}
}
class Tablet {
let model: String
var owner: User?
init(model: String) {
self.model = model
print("생성: Tablet (self.model)")
}
deinit {
print("소멸: Tablet (self.model)")
}
}
!29
🧒

!30!30!30
strong strong
<User Instance>
name: “Dana”
weak
<Tablet Instance>
strong
var iPadProvar dana
// 새로 샀다!!
// 박살남
iPadPro = nil

!31!31!31
strong
weak
<Tablet Instance>
strong
var iPadProvar 흰
<User Instance>
name: “Dana”
var dana
// 새로 샀다!!
// 박살남
iPadPro = nil

!32!32!32
strong
weak
var iPadPro
<User Instance>
name: “Dana”
var dana
// 새로 샀다!!
// 박살남
iPadPro = nil

!33!33!33
strong
var iPadPro
<User Instance>
name: “Dana”
var dana
nil
// 집 나감 🤬
dana = nil
// 새로 샀다!!
// 박살남
iPadPro = nil

!34!34!34
strong
var iPadPro
<User Instance>
name: “Dana”
var dana
nil
// 집 나감 🤬
dana = nil
// 새로 샀다!!
// 박살남
iPadPro = nil

!35!35!35
var iPadPro
<User Instance>
name: “Dana”
var dana
nil
// 집 나감 🤬
dana = nil
// 새로 샀다!!
// 박살남
iPadPro = nil

!36!36!36
var iPadProvar dana
// 집 나감 🤬
dana = nil
// 새로 샀다!!
// 박살남
iPadPro = nil

!37!37!37
Unowned Reference
Class NetﬂixMembershipClass User
class NetflixMembership {
let plan: String
let owner: User
init(plan: String, owner: User) {
self.plan = plan
self.owner = owner
print("생성: (self.plan) 구독")
}
deinit {
print("소멸: (self.plan) 구독")
}
}
class User {
let name: String
var netflixMembership:
NetflixMembership?
self.name = name
}
deinit {
}
}
unowned let owner: User
🧒

!38!38!38
해결 - Unowned Reference
var dana
var dana: User? = User(name: “Dana")
dana!.netflixMembership = NetflixMembership(plan: "Premium", owner: dana!)

!39!39!39
var 흰
strong
<User Instance>
name: “Dana”
streamingMembership:

<StreamingMembership Instance>
var dana

!40!40!40
strong
<NetﬂixMembership Instance>
Plan : “Premium”
strong
<User Instance>
name: “Dana”

var dana

!41!41!41
strong
strong
unowned
<User Instance>
name: “Dana”

var dana

!42!42!42
strong
strong
unowned
// 탈퇴..
Dana = nil
<User Instance>
name: “Dana”

var dana

!43!43!43
strong
unowned
// 탈퇴..
Dana = nil
<User Instance>
name: “Dana”

var dana

!44!44!44
unowned
// 탈퇴..
Dana = nil
var dana

!45!45!45
// 탈퇴..
Dana = nil
var dana

!46
Strong Reference Cycle for Closure
class User {
let name: String
var nickName: String?
init(name: String, nickName: String? = nil) {
self.name = name
self.nickName = nickName
}
lazy var completeUserName: () -> String = {
if let nickName = self.nickName {
return "(self.name) ((nickName))"
} else {
return "(self.name)"
}
}
deinit {
print("탈퇴: User (self.name)")
}
}

class User {
let name: String
self.name = name
}
} else {
}
}
deinit {
}
}
!47
var dana: User? =
User(name: "Dana", nickName: "white")
print(dana!.completeUserName())
dana = nil
var dana
<User Instance>
name: “Dana”
nickName: “white”
completeUserName:

( ) -> String
( ) -> String
self.name self.nickName
strong
strong
strong

!48
var 흰
( ) -> String
strong
class User {
let name: String
self.name = name
}
} else {
}
}
deinit {
}
}
strong
var dana
<User Instance>
name: “Dana”
completeUserName:

( ) -> String
var dana: User? =
dana = nil

class User {
let name: String
self.name = name
}
[unowned self] in
} else {
}
}
deinit {
}
}
!49
var 흰
( ) -> String
unowned
strong
strong
해결 - Capture List
var dana
<User Instance>
name: “Dana”
completeUserName:

( ) -> String
var dana: User? =
dana = nil

class User {
let name: String
self.name = name
}
[unowned self] in
} else {
}
}
deinit {
}
}
!50
var 흰
( ) -> String
unowned
strong
var dana
<User Instance>
name: “Dana”
completeUserName:

( ) -> String
var dana: User? =
dana = nil

class User {
let name: String
self.name = name
}
[unowned self] in
} else {
}
}
deinit {
}
}
!51
( ) -> String
unowned
var dana
var dana: User? =
dana = nil

class User {
let name: String
self.name = name
}
[unowned self] in
} else {
}
}
deinit {
}
}
!52
var dana
var dana: User? =
dana = nil

!53
Summary 📌
메모리 관리 필요성
Reference Counting : 필요로 하는 애들의 수를 세자
Swift Compiler, ARC / MRC
Strong Reference Cycle : 메모리 공간 낭비의 원인
Weak / Unowned : 상대적 수명에 대한 정보를 제공해주자
Closure : of Reference Type. Capture List

!54
Strong / Weak / Unowned
raywenderlich - ARC and Memory Management in Swift

!55
Reference 📗
✦ Swift Language Guide - Automatic Reference Counting
✦ raywenderlich - ARC and Memory Management in Swift
✦ WWDC 2015 - Optimizing Swift Performance
✦ WWDC 2016 - Understanding Swift Performance
✦ ARC Release Note
✦ Soulpark blog - Automatic Reference Counting (ARC)

!56
더 알아보기 🔍
✦ Value type이 메모리에서 관리되는 방식
✦ Understanding Swift Performance - WWDC 2016
✦ 메모리 관리 방식을 고려한 Swift 성능 올리기
✦ Optimizing Swift Performance - WWDC 2015
✦ Understanding Swift Performance - WWDC 2016
✦ Object-C 에서 MRC/ARC
✦ ARC obj-c
✦ Transition to ARC (no longer supported?)
✦ 고급언어의 컴파일러와 프로그램의 로딩
✦ Garbage Collector 와 ARC 의 차이

Swift - ARC와 메모리 관리

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