On Tue, 09 Apr 2013 15:55:09 -0400, Henning Pohl <[email protected]>
wrote:
In fact there is no order of destruction. And this is one of the most
annoying D problems I recently had to deal with. Look at this example:
http://dpaste.dzfl.pl/f3f860b0. This time, it segfaulted. Next time it
may (in theory) not, because the dtor of a is called before the one of
b. A holds a reference to a B. In the destructor of A I expect b either
to be null or a valid instance of B (which has not been destroyed yet).
You get a kind of undefined behavior instead. This is IMO a huge
drawback towards reference counting with strong/weak references.
Is there right now any way to arrange things?
No. You are not allowed to access any GC-managed resources inside a
destructor.
And it won't be null, because that would be extremely costly. Consider if
300 objects had a pointer to a block of memory. Now those 300 objects all
go away. By your expectation, if the targeted block of memory was
collected, the GC would have to spend time going through all those 300
pointers, setting them to null. When they are about to all be destroyed.
99.99% of the time, that would be wasted, as those 300 objects may not
even have destructors that care.
A destructor is ONLY for destroying non-GC managed resources, nothing
else. Like an OS file handle for instance.
-Steve
