I am Developer! :: 프록시 패턴

객체를 사용하는 시점까지 생성과 초기화에 드는 비용 및 시간을 절약하기위해, 다른 객체에 접근하여 중간 대리 역할을 하는 객체를 만드는 패턴. 예) 객체의 생성이 완료되기 이전에 이 객체를 가상으로 사용할 수 있는 방법을 제공하여, 실제 객체가 필요한 경우만 proxy를 생성하여 부하를 최소화 하는데, 외부에서는 실행되는 진짜 객체가 보이지 않는다.

Before
Direct coupling, lots of start-up and shut-down overhead.

class Image { int m_id; static int s_next; public: Image() { m_id = s_next++; cout << " $$ ctor: " << m_id << '\n'; } ~Image() { cout << " dtor: " << m_id << '\n'; } void draw() { cout << " drawing image " << m_id << '\n'; } }; int Image::s_next = 1; int main() { Image images[5]; for (int i; true;) { cout << "Exit[0], Image[1-5]: "; cin >> i; if (i == 0) break; images[i - 1].draw(); } }

$$ ctor: 1

$$ ctor: 2

$$ ctor: 3

$$ ctor: 4

$$ ctor: 5

Exit[0], Image[1-5]: 2

drawing image 2

Exit[0], Image[1-5]: 4

drawing image 4

Exit[0], Image[1-5]: 2

drawing image 2

Exit[0], Image[1-5]: 0

dtor: 5

dtor: 4

dtor: 3

dtor: 2

dtor: 1

After

Initialization on ﬁrst use

Design an “extra level of indirection” wrapper class
The wrapper class holds a pointer to the real class
The pointer is initialized to null
When a request comes in, the real object is created “on ﬁrst use” (aka lazy intialization)
The request is always delegated

class RealImage
{
    int m_id;
  public:
    RealImage(int i)
    {
        m_id = i;
        cout << "   $$ ctor: " << m_id << '\n';
    }
    ~RealImage()
    {
        cout << "   dtor: " << m_id << '\n';
    }
    void draw()
    {
        cout << "   drawing image " << m_id << '\n';
    }
};

// 1. Design an "extra level of indirection" wrapper class
class Image
{
    // 2. The wrapper class holds a pointer to the real class
    RealImage *m_the_real_thing;
    int m_id;
    static int s_next;
  public:
    Image()
    {
        m_id = s_next++;
        // 3. Initialized to null
        m_the_real_thing = 0;
    }
    ~Image()
    {
        delete m_the_real_thing;
    }
    void draw()
    {
        // 4. When a request comes in, the real object is
        //    created "on first use"
        if (!m_the_real_thing)
          m_the_real_thing = new RealImage(m_id);
        // 5. The request is always delegated
        m_the_real_thing->draw();
    }
};
int Image::s_next = 1;

int main()
{
  Image images[5];

for (int i; true;)
  {
    cout << "Exit[0], Image[1-5]: ";
    cin >> i;
    if (i == 0)
      break;
    images[i - 1].draw();
  }
}

Exit[0], Image[1-5]: 2

$$ ctor: 2

drawing image 2

Exit[0], Image[1-5]: 4

$$ ctor: 4

drawing image 4

Exit[0], Image[1-5]: 2

drawing image 2

Exit[0], Image[1-5]: 0

dtor: 4

dtor: 2

출처 : http://sourcemaking.com/design_patterns
http://softrami.tistory.com/entry/Design-Patterns-Proxy-Pattern

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I am Developer!

프록시 패턴 - Proxy in C++

Before
Direct coupling, lots of start-up and shut-down overhead.

After

Initialization on ﬁrst use

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태터데스크 관리자

태터데스크 메시지

I am Developer!

프록시 패턴 - Proxy in C++

Before Direct coupling, lots of start-up and shut-down overhead.

After

Initialization on ﬁrst use

Categories

Recent Comments

Before
Direct coupling, lots of start-up and shut-down overhead.