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boost::intrusive_ptr problem

oliii · 2009-09-25T09:05:31

I run into this problem... Quote: #include <memory.h> #include <stdio.h> #include <boost/smart_ptr.hpp> #define DECLAREREF(Type) class Type; typedef boost::intrusive_ptr<Type> Type##Ref; #define NULLREF(Type) boost::intrusive_ptr<Type>() template<typename Type> boost::intrusive_ptr<Type> MAKEREF(Type* object) { return boost::intrusive_ptr<Type>(object); } template<typename Type> bool ISNULLREF(const boost::intrusive_ptr<Type>& ref) { ref == boost::intrusive_ptr<Type>(); } namespace boost { class Referencable { protected: Referencable() : refcount_(0) {} long refcount_; virtual void incRef() { (++refcount_); } virtual void decRef() { if((--refcount_) == 0) delete this; } private: friend void intrusive_ptr_release(Referencable * p); friend void intrusive_ptr_add_ref(Referencable * p); }; void intrusive_ptr_add_ref(Referencable * p) { p->incRef(); } void intrusive_ptr_release(Referencable * p) { p->decRef(); } } class DummyClass { public: virtual ~DummyClass(){} virtual bool doSomethingVirtual()=0; }; DECLAREREF(Object); class Object: public DummyClass, public boost::Referencable { public: Object() {} virtual ~Object() {} virtual bool doSomethingVirtual() { return true; } }; #ifdef WIN32 #include <windows.h> // Include the much need windows.h int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hprev, PSTR cmdline, int ishow) #else void main() #endif { ObjectRef object = MAKEREF(new Object()); object = NULLREF(Object); } Basically, I have a base class Referencable, that implements reference counting and release. Objects needed intrusive pointer support are derived from it. The problem comes with multiple inheritance. The Object is also derived from another class. Quote: class Object: public DummyClass, public boost::Referencable { //.... }; this throws an exception at the pointer deletion, the Referencable pointer if offset by 4 bytes from the Object pointer. if I do this Quote: class Object: public boost::Referencable, public DummyClass { //.... }; It's fine. I don't like it. I'm not sure if it's wrong and I am an imbecile, or if there is a better way to do this without having to worry about multiple inheritance. I'd like to derive the 'Referencable' so I can use it for a recycle bin (which I do and works fine so far).

General and Gameplay Programming Programming

Started by oliii September 23, 2009 11:15 AM

12 comments, last by oliii 14 years, 6 months ago

BitMaster

8,652

September 25, 2009 02:31 AM

Well, as I said earlier what a shared_ptr does when the lifetime of the managed object has ended can be easily configured:

void moveToPool(MyObject* obj) { ... }typedef shared_ptr<MyObject> MyObjectPointer;...MyObjectPointer pObject(new MyObject(...), moveToPool);

In the above example the function moveToPool will be called when the last instance of the shared pointer expires. Note that you can copy the shared_ptr as often as you want, all instances will keep track of the deleter function.

This is also very useful if you want to manage an entity which has to be cleaned up by a library function instead of delete (for example cvReleaseImage in OpenCV).

DevFred

840

September 25, 2009 04:34 AM

Quote:Original post by oliii
Why not?

Because if your only reason whas this:

Quote:Original post by oliii
- No heap allocation required for the ref counter.

Then I would have yelled make_shared ;)

It's a function in boost that heap allocates the object and the refcount with a single allocation.

Kylotan

10,510

September 25, 2009 04:59 AM

That make_shared looks pretty handy, as I'd been concerned about the performance implications too. Even searching the Boost mailing list implied this was still an issue. It's a shame that the Boost libraries are so sprawling and difficult to keep track of - who knows how many useful things pass us by.

oliii

2,202

Author

September 25, 2009 09:05 AM

Quote:Original post by BitMaster
Well, as I said earlier what a shared_ptr does when the lifetime of the managed object has ended can be easily configured:

*** Source Snippet Removed ***

In the above example the function moveToPool will be called when the last instance of the shared pointer expires. Note that you can copy the shared_ptr as often as you want, all instances will keep track of the deleter function.

This is also very useful if you want to manage an entity which has to be cleaned up by a library function instead of delete (for example cvReleaseImage in OpenCV).

That's interesting, I'll look into that. make_shared() also good :)

Everything is better with Metal.

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