Destructing Member Objects

[Christopher Wright]

Simen Kjaeraas wrote:
> On Sun, 06 Apr 2008 06:27:52 +0200, Jarrett Billingsley 
> <kb3ctd2 at yahoo.com> wrote:
> 
>> The spec doesn't really specify _why_ destruction order is 
>> nondeterministic,
>> however.  You need nondeterministic destruction in order to break cycles.
>> So if A points to B and B points to A, you have a cycle.  In order to 
>> break
>> the cycle you have to delete one or the other first.  There's no 
>> "correct"
>> order to destroy them.  So, to solve this, you simply cannot guarantee 
>> that
>> when an object's destructor is run, that everything that it points to is
>> still valid.
> 
> It's worth noting that even if only one object in a relation points to
> another (i.e. no cycle), the easiest thing for the GC to do is to flag both
> as trash, then destroy them in some order when it gets to that point. If it
> were to flag only the mother class and destroy that, its child classes 
> might
> have to wait until the next GC run before they're deleted.
> 
> -- Simen

That doesn't work. The collector flags stuff only as not-trash, never as 
trash. Then it does a linear scan through each block containing 
aggregate types and calls destructors.

Well, maybe not, but that's how I'd implement it, if I cared about 
efficiency.