Re: [Boost-users] [smart_ptr] Conflict with Maya?

From: Andrew Holden (aholden_at_[hidden])
Date: 2007-04-19 09:32:43

Paul Giaccone wrote:
>
>Peter Dimov wrote:
>
>>Paul Giaccone wrote:
>>
>>  
>>
>>>1. The creator function, required by Maya. Note the absence of a
smart
>>>pointer. I tried wrapping this in a shared_ptr and returning .get()
>>>but this caused a crash, if I remember rightly.
>>>
>>>void* MyNode::creator(void)
>>>{
>>>   return new MyNode();
>>>}
>>>    
>>>
>>
>>This is, I think, exactly as it should be. Maya expects to take
ownership >>of 
>>the returned pointer and will delete it when it decides that it's no
>>longer 
>>needed. But I'm not an expert on that; you probably need to ask in a
Maya 
>>SDK forum to be sure. 
>>  
>>
>
>A bit of research and feedback from HighEnd 3D's Maya API forum
suggests 
>that this is the case - you create the node and Maya takes 
>responsibility deleting it when necessary. Apparently, Maya owns the 
>node and deletes it itself when it feels like it, not when the 
>programmer says so.
>
>If I've understood correctly, this means that any memory allocated on 
>the heap in MyNode must be done using bare pointers rather than smart 
>pointers, so that Maya can delete it when it wants, not when the smart 
>pointers say the memory can be released. MyNode and any objects that it

>allocates on the heap still need to have destructors to deallocate
their 
>contents, but it is up to Maya when the destructor for MyNode is
called.
>
>Not an ideal state of affairs (once you've experienced smart pointers, 
>you never want to go back to the inconvenience of having to work out 
>where the all the deletes need to go), but then I've found that Maya is

>hardly the most programmer-friendly system, IMO.

First, let me say that I am not familiar with Maya, so I may not know
what I am talking about.

That said, are there still some objects you need to delete manually?  I
think you can still use smart pointers for those, and save the raw
pointers for objects you pass back to Maya (like the pointer returned
from MyNode::creator).

The only problem I can see with this is if you have an object that Maya
MIGHT delete for you, or that you might need to delete yourself.  If you
get to deal with that kind of ugliness, maybe you can use a custom
deleter that checks some sort of flag before deleting the object.  If
you can put this flag in the object itself, then it is a simple matter
of setting it before you give the object to Maya.  If you can't, then it
would probably be easier to use raw pointers for that object.