Re: [boost] request for interest in a garbage collection library

Subject: Re: [boost] request for interest in a garbage collection library
From: Achilleas Margaritis (axilmar_at_[hidden])
Date: 2009-04-20 13:03:59

Jonas Persson wrote:
> Achilleas Margaritis skrev:
>> Can you please elaborate on the problem of destructors? I have read 
>> some papers that say that gc and destructors don't play well together, 
>> but I did not really agree with that. An example would be appreciated.
> 
> One example is that, by default, your gc do not handle cyclic 
> dependencies correct because destructors are run when collected.
> 
> The following example gives an access violation on windows:
> 
> ----------------------------------------------
>   class Foo : public gc_object<Foo> {
>   public:
>     gc_ptr<Foo> m_next;
>     std::string m_name;
> 
>     Foo(std::string name) : m_name(name) {}
> 
>     ~Foo() {
>       m_next->lastGoodbye();
>     }
> 
>     void lastGoodbye() { std::cout << "Bye " << m_name; }
>   };
>   void test_cycle() {
>     gc_ptr<Foo> foo1 = new Foo("foo 1");
>     foo1->m_next = new Foo("foo 2");
>     foo1->m_next->m_next = foo1;
> 
>     foo1 = 0;
>     gc::collect();
>   }
> ----------------------------------------------

But gc'd objects are are not supposed to touch other gc'd objects in 
their destructor (if you check the readme, I explicitly say that the 
order of finalization is random). Is there a realistic need to call 
another gc'd object from a destructor?