Difference between revisions of "HOWTO resolve circular references in ns-3 memory disposal"

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(HOWTO resolve smart pointer circular references in ns-3 memory disposal)
(HOWTO resolve smart pointer circular references in ns-3 memory disposal)
Line 48: Line 48:
 
         a->m_callback = MakeCallback (&B::CallbackMethodB, b);
 
         a->m_callback = MakeCallback (&B::CallbackMethodB, b);
 
         b->AggregateObject(a);
 
         b->AggregateObject(a);
         b->Dispose(); //a->Dispose() will work as well.  Both will end up calling DoDispose in object a which breaks the reference cycle
+
         b->Dispose();  
 +
        //a->Dispose() will work as well.  Both will end up calling DoDispose  
 +
        //in object a which breaks the reference cycle
 
     }
 
     }
 
     </pre>
 
     </pre>

Revision as of 18:00, 30 August 2013

HOWTO resolve smart pointer circular references in ns-3 memory disposal

    class A : public Object
    {
    public:
       static TypeId GetTypeId (void);
       Callback<void> m_callback;
    };
    class B : public Object
    {
    public:
       static TypeId GetTypeId (void);
       void CallbackMethodB (void);
    };
     int main(int argc, char* argv[])
     {
        Ptr<A> a = CreateObject<A>();
        Ptr<B> b = CreateObject<B>();
        a->m_callback = MakeCallback (&B::CallbackMethodB, b);
        b->AggregateObject(a);
     }
     
    ==15749== LEAK SUMMARY:
    ==15749==    definitely lost: 40 bytes in 1 blocks
    ==15749==    indirectly lost: 152 bytes in 5 blocks
    ==15749==    possibly lost: 0 bytes in 0 blocks

The preferred way to break reference cycles like this in ns-3 is to use Object::Dispose(). This method will call the DoDispose method on the object that it is called on as well as all other objects aggregated on to it. In the above example Class A is aggregated to Class B so we make the following change to Class A:

    class A : public Object
    {
    public:
       static TypeId GetTypeId (void);
       Callback<void> m_callback;
       virtual void DoDispose (void)
       {
          m_callback = MakeNullCallback<void>();
       }	
    };

Now the following code:

     int main(int argc, char* argv[])
     {
        Ptr<A> a = CreateObject<A>();
        Ptr<B> b = CreateObject<B>();
        a->m_callback = MakeCallback (&B::CallbackMethodB, b);
        b->AggregateObject(a);
        b->Dispose(); 
        //a->Dispose() will work as well.  Both will end up calling DoDispose 
        //in object a which breaks the reference cycle	
     }
     

will no longer have a memory leak.

    ==16877== LEAK SUMMARY:
    ==16877==    definitely lost: 0 bytes in 0 blocks
    ==16877==    indirectly lost: 0 bytes in 0 blocks
    ==16877==    possibly lost: 0 bytes in 0 blocks

Note for many ns