Simple Example

• Example 1
  • using System;
    class A
    {
       public A() { Console.WriteLine("Creating A"); }
      ~A() { Console.WriteLine("Destroying A"); }
    }
  • class B : A
    {
       public B() { Console.WriteLine("Creating B"); } 
       ~B() { Console.WriteLine("Destroying B"); }
    }
  • class C : B
    {
         public C() { Console.WriteLine("Creating C"); }
          ~C() { Console.WriteLine("Destroying C"); }
    }
  • class App
    {
         public static void Main()
        {
              C c = new C();
              Console.WriteLine("Object Created ");
              Console.WriteLine("Press enter to Destroy it");
             Console.ReadLine();
             c = null;
             Console.Read();
         }
    }
  • result
    }
• Example 2
  • using System;
    class A
    {
        public A() { Console.WriteLine("Creating A"); }
        ~A() { Console.WriteLine("Destroying A"); }
    }
  • class B : A
    {
         public B() { Console.WriteLine("Creating B"); }
         ~B() { Console.WriteLine("Destroying B"); }
    }
  • class C : B
    {
         public C() { Console.WriteLine("Creating C"); }
         ~C() { Console.WriteLine("Destroying C"); }
    }
  • class App
    {
        public static void Main()
       {
             C c = new C();
             Console.WriteLine("Object Created ");
              Console.WriteLine("Press enter to Destroy it");
            Console.ReadLine();
           c = null;
            GC.Collect();
           Console.Read();
       }
    }
  • result
    

• Unmaged Heap Memory:
  • for C,C++ , Memeorry Alocation, insances
  • cannot be reachable by GC
  • use pointer
• Managed Heap Memory
  • for .net,
  • reachable by GC,
  • no pointer => the rumtime can do memory magagenemt

Garbage Collector(GC) in .net

• concept
  • Thread
  • 생성된 객체중에서 접근이 불가능한 객체의 메모리를 수집하여 해제한다.
  • The task of garbage collection is a costly process
  • GC의 실행시기
    • when a call to create a new object fails due to lack of memory
      managed heap memory가 부족할 때(다른 객체의 생성이 불가능 때)
    • when the user explicitly calls GC thread to do garbage collection by calling the function GC.Collect().
  • GC can recollect memory from only those objects which are no longer accessible in your code by any reference
  • if a function goes out of scope,
    • all its local objects will be eligible for garbage collection, unless and until of course the local objects have their references passed outside the function
  • In the case of the windows service,
    • there might be some objects which are no longer required to be referenced but still have references pointing to them.
    • So for them to be eligible to Garbage Collection I have to remove all the references to these objects programmatically
• 예1
  • void A() {
    B(); //1
    int i = 10; //2
    }
    void B() {
    C c = new C();
    Console.WriteLine(c.Name);
    }
  • 실행이 문장 2에 도달하면 B()에서 생성돤 객체 c늬 접근이 불가하므로 다음 GC가 실행될때 c츼 객체는 해제된다.
• 예 2
  • class A {
    pribate B b; // line 3
    public void RequiredB() {
    b = new B(); //line 4
    b.DoSomeWork();
    b=null; //line 5
    }
  • 함수 RequiredB가 실행이 완료되어도 line2의 참조 b 때문에 객체 B가 유지된다. RequiredB()의 실행이 종료되면 참조 nuul로 참조 b를 세팅하여 객체 B를 GC가 가능하게 하였다.
• Multi Reference
  • class A
    {
    private B b; //reference now points to nothing, trying to use this directly will give NullPointerException
    private B b2; //another empty reference which points to nothing
    public void RequireB()
    {
    b = new B(); //Set this reference to an object
    b2 = b; //Also set b2 as reference to the same object pointed by b Now object created above by calling new B() has 2 references b and b2
    b2.DoSomeWork(); //b2.DoSomeWork is same as b.DoSomeWork() as both point to same object
    b = null; //Just doing this will not make the object eligible for garbage collection because even b2 is pointing to it. So you need the line below too! Else there will be a memory leakage
    b2=null;
    }
    }
• Dispose, IDisposable
  • B b = new B();
    using (b)
    {
    // use b
    } // here compiler will call Dispose on b's IDisposable implementation automatically
• • class K
    {
    K() {}
    void Finalize() //GC가 자동 호출
    {
    base.Finalize();
    }
    }

• • class B : IDisposable
    {
    public void Dispose()
    {
    //Do all cleanup activities
    GC.SuppressFinalize(); //prevent Finalize() being called in GC
    }
    ~B()
    {
    Dispose();
    }
    }

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