Question

I just got burned by a bug that is partially due to my lack of understanding, and partially due to what I think is suboptimal design in our codebase. I’m curious as to how my 5-minute solution can be improved.

We’re using ref-counted objects, where we have AddRef() and Release() on objects of these classes. One particular object is derived from the ref-count object, but a common function to get an instance of these objects (GetExisting) hides an AddRef() within itself without advertising that it is doing so. This necessitates doing a Release at the end of the functional block to free the hidden ref, but a developer who didn’t inspect the implementation of GetExisting() wouldn’t know that, and someone who forgets to add a Release at the end of the function (say, during a mad dash of bug-fixing crunch time) leaks objects. This, of course, was my burn.

 void SomeFunction(ProgramStateInfo *P) {    ThreadClass *thread = ThreadClass::GetExisting( P );    // some code goes here    bool result = UseThreadSomehow(thread);    // some code goes here    thread->Release();  // Need to do this because GetExisting() calls AddRef() } 

So I wrote up a little class to avoid the need for the Release() at the end of these functions.

 class ThreadContainer { private:     ThreadClass *m_T; public:     ThreadContainer(Thread *T){ m_T = T; }     ~ThreadContainer() { if(m_T) m_T->Release(); }     ThreadClass * Thread() const { return m_T; } }; 

So that now I can just do this:

 void SomeFunction(ProgramStateInfo *P) {    ThreadContainer ThreadC(ThreadClass::GetExisting( P ));    // some code goes here    bool result = UseThreadSomehow(ThreadC.Thread());    // some code goes here    // Automagic Release() in ThreadC Destructor!!! } 

What I don’t like is that to access the thread pointer, I have to call a member function of ThreadContainer, Thread(). Is there some clever way that I can clean that up so that it’s syntactically prettier, or would anything like that obscure the meaning of the container and introduce new problems for developers unfamiliar with the code?

Thanks.

Answer 1

use boost::shared_ptr it is possible to define your own destructor function, such us in next example: http://www.boost.org/doc/libs/1_38_0/libs/smart_ptr/sp_techniques.html#com