[Boost-users] shared_ptr memory leak

Subject: [Boost-users] shared_ptr memory leak
From: gast128 (gast128_at_[hidden])
Date: 2009-02-26 15:58:00

Dear all,

we managed to create a shared_ptr memory leak, without making a cycle. Granted 
it is highly controversial case. One has to make call in the destructor of the 
owned object which loops back to the point of assignment.

Is this something for the documentation, or may this indeed be flagged as 
a 'nut' case.

Code below is a simplified example, the production case was with some kind of 
change manager which notification bounced back to the point of assignment. One 
has to split out header and cpp to get it compilable.

void TestSharedPtrLeak()
{
   //make the leak
   KTestBoostHlpSpLeakParent leak;
   leak.Reset(false);
}

//ktestboosthlpspleakparent.h
struct KTestBoostHlpSpLeakParent
{
   KTestBoostHlpSpLeakParent();
   
   void Reset(bool b);
   
   boost::shared_ptr<KTestBoostHlpSpLeak>  m_ptr;
};

//ktestboosthlpspleakparent.cpp
KTestBoostHlpSpLeakParent::KTestBoostHlpSpLeakParent()
{
   Reset(true);
}

void KTestBoostHlpSpLeakParent::Reset(bool b)
{
   boost::shared_ptr<KTestBoostHlpSpLeak> ptr(new KTestBoostHlpSpLeak(this, 
b));
   
   m_ptr = ptr;
   //m_ptr.swap(ptr); //would solve it btw
}

//ktestboosthlpspleak.h
struct KTestBoostHlpSpLeak
{
   KTestBoostHlpSpLeak(KTestBoostHlpSpLeakParent* p, bool b);
   ~KTestBoostHlpSpLeak();
   
public:
   KTestBoostHlpSpLeakParent* m_p;
   bool                       m_b;
};

//ktestboosthlpspleak.cpp
KTestBoostHlpSpLeak::KTestBoostHlpSpLeak(KTestBoostHlpSpLeakParent* p, bool b)
 : m_p(p)
 , m_b(b)
{
}

KTestBoostHlpSpLeak::~KTestBoostHlpSpLeak()
{
   if (m_b)
   {
      //recursive call
      m_p->Reset(false);
   }
}