Re: [boost] library proposal: garbage collection

From: Larry Evans (cppljevans_at_[hidden])
Date: 2006-01-12 07:31:30

On 01/11/2006 10:39 AM, Achilleas Margaritis wrote:
[snip]
>>   1) allocated the storage for the pointee
>>   2) stored the last-created-pointer in some thread-local-storage
>>   3) created the pointee with placement new (this requiring
>>      knowlege about the pointee's CTOR)
>>   4) then zeroed the last-created-pointer
>>
>>Does this make sense?
>>[snip]
> 
> 
> No, the new object will be placed in a thread-local-storage list by operator 
> new.
> 
> Here is the sequence of operations:
> 
> 1) operator new is invoked: it allocates memory for the new block and places 
> the block in a thread-local-storage object list.
> 2) gc_ptr::CTOR is invoked: it looks at the last entry of the 
> thread-local-storage object list. If not inside that block, it adds itself 
> to the thread-local-storage pointer stack.
>
OK, but in my mental trace of the following code:
<------------- cut here --------------
class MyClass : public gc_object {
public:
     gc_ptr<MyClass> other;
     MyClass(unsigned n=0)
       : other(n?new MyClass(n-1):(MyClass1*)0)
     {}
};

MyClass on_stk(3);

 >-------------- cut here -------------
The only gc_ptr on the stack is on_stk.other; yet,
the others are put on the stack because, in each
case, the last created gc_object is the one
used in the argument to the gc_ptr CTOR.

Am I missing something?  If so, could you
maybe do a quick prototype to illustrate
what I'm missing?

TIA.