Release() and how that works...

Cyelince · 2002-02-19T20:22:47

Okay, I was wondering, how the Release() thing works found so often in the DirectX Interfaces...I noticed, you never ''delete'' them. You just Release() and make them NULL. I made a class like that and did some tests. Anyone else know if this is actually valid or not? I didn''t include the #includes though... class MemTestR { public: MemTestR(): m_ref(1) {}; int Release() { int tmp = --m_ref; if(m_ref<=0) delete(this); return(tmp); } int m_ref; int m_x, m_y; }; ///---------------------------------------------------------------------------- // // // main() // // ///---------------------------------------------------------------------------- int main() { { MemTestR * mtr = NULL; mtr = new MemTestR; mtr->m_x = 0; mtr->m_y = 0; printf("\nX:%i\nY:%i\nRef:%i\n", mtr->m_x, mtr->m_y, mtr->m_ref); int tmp = mtr->Release(); printf("\nX:%i\nY:%i\nRef:%i\n", mtr->m_x, mtr->m_y, tmp);//mtr->m_ref); } /// doesn''t work if you don''t make it a pointer... { MemTestR mtr; mtr.m_x = 0; mtr.m_y = 0; printf("\nX:%i\nY:%i\nRef:%i\n", mtr.m_x, mtr.m_y, mtr.m_ref); int tmp = mtr.Release(); printf("\nX:%i\nY:%i\nRef:%i\n", mtr.m_x, mtr.m_y, tmp);//mtr->m_ref); } printf("\n\nDone\n"); return(0); }

Graphics and GPU Programming Programming

Started by Cyelince February 17, 2002 09:23 PM

18 comments, last by Cyelince 22 years, 1 month ago

CGameProgrammer

640

February 17, 2002 11:09 PM

Your Release is fine, though it''s useless without an AddRef. But yeah, that''s how you''d do it.

I wrote a smart pointer class, although I eventually decided not to bother using it. But it was this:

  template <class Type> class pointer{    public:         pointer ( )        {            m_Object = NULL;        }         pointer ( Type* Object )        {            m_Object = Object;            if( m_Object )                m_Object->AddRef( (object**)&m_Object );        }         ~pointer ( )        {            if( m_Object )                m_Object->Release( );        }         inline operator = ( Type* Object )        {            if( m_Object )                m_Object->Release( );            m_Object = Object;            if( m_Object )                m_Object->AddRef( (object**)&m_Object );        }         inline Type* operator -> ( ) const        {            return m_Object;        }         inline Type* operator () ( ) const        {            return m_Object;        }         inline operator Type* ( ) const        {            return m_Object;        }         inline bool operator == ( Type* Object ) const        {            return m_Object == Object;        }         inline bool operator != ( Type* Object ) const        {            return m_Object != Object;        }         inline operator bool ( ) const        {            return m_Object ? true : false;        }     private:         Type*       m_Object;};

The object had to be derived from a base object that had the AddRef and Release methods. All my classes are derived from a common base class (except pointer) so I could do things like this.

It would be used like this:

  pointer<OpenGL> pGL = new OpenGL; // Create it.pGL->SetDisplayMode( 640, 480, 16 ); // Do something.pGL = NULL; // This releases the object.

~CGameProgrammer( );

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Fruny

1,658

February 17, 2002 11:30 PM

CGameProgrammer, there is a problem with your assignment operator (just what I had warned about in my code)

if Object == m_Object, the fact that you call release first may cause the object to be destroyed.

// if m_Object == Object, release Object, which may be deletedif( m_Object ) m_Object->Release( ); // This line would basically be a no-opm_Object = Object;// m_Object could now be a dangling pointer... calling AddRef would segfault.if( m_Object )    m_Object->AddRef( (object**)&m_Object );

"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." — Brian W. Kernighan

CGameProgrammer

640

February 18, 2002 07:26 PM

Actually, it won''t, I don''t think. Unless you say pGL = pGL of course. I suppose it''s not a bad idea checking to make sure m_Object isn''t the same as Object, but since only bad programming would cause that situation to arise, I wouldn''t waste a conditional jump.

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IndirectX

122

February 19, 2002 01:10 AM

If you wouldn''t waste that jump, why does EVERY single reference counted pointer class I''ve seen (including those in ATL) do?

---visit #directxdev on afternet <- not just for directx, despite the name

CGameProgrammer

640

February 19, 2002 09:57 AM

Probably because they may be used in bad programming. When making public libraries like that, you want to be extra-careful. But for your own code, you can make optimizations if you know it won''t be a problem for you.

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Fruny

1,658

February 19, 2002 11:56 AM

It is critical to ensure correctness first, then speed.
If you are working in any kind of professional situation, you don''t know who will go through your code after you.

IndirectX

122

February 19, 2002 03:15 PM

I agree with Fruny. In any event, it''s always better to waste a jump rather than to spend half a day debugging your program when you in fact do assign a pointer to itself. If you are extremely concerned with performance, at least put an ASSERT in there. However, I doubt that you''ll see any speed difference just because you don''t check this case.

Correctness is also why I wrap every single DX interface method I use, and check all HRESULTs. I know that DrawPrimitive doesn''t fail unless you give it a NULL pointer, but I once had a problem even with it.

---visit #directxdev on afternet <- not just for directx, despite the name

Oluseyi

2,123

February 19, 2002 03:27 PM

#include "atlbase.h"//#include "d3d8.h"#pragma comment( lib, "d3d8.lib" )#pragma comment( lib, "dxguid.lib" )//...CComPtr<IDirect3D8 *> pd3d;//...int WINAPI WInMain(..){  pd3d.Attach( ::Direct3D8Create(D3D_SDK_VERSION, ...) );  // no need to call release; CComPtr does that automatically  // could also have used CComQIPtr which supports QueryInterface}

Cyelince

122

Author

February 19, 2002 03:28 PM

Thanks everybody for all the input...even though it seems like the subject changed a bit. I will probably just use regular pointers though. Not sure...anyway, I guess it seems okay to have a method in a class delete itself like in my Release() method, as long as it''s a pointer.

Cocyen

IndirectX

122

February 19, 2002 08:22 PM

Just make sure you allocate your classes with new.

---visit #directxdev on afternet <- not just for directx, despite the name

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