Re: [boost] Re: shared_ptr: unsafe, or am I crazy?

From: George A. Heintzelman (georgeh_at_[hidden])
Date: 2002-01-18 15:52:01

Peter Dimov wrote:
> George Heintzelman wrote:
> > I don't like adding the extra layer of indirection for *all* shared_ptr
> > destructor calls, in order to 'solve' this, for the destructor case
> > only. In a policy-based smart pointer, I would support making it an
> > available policy but not the default one.
> 
> I'd be surprised if you could measure the added cost. Besides, the extra
> layer of indirection has other good uses. It makes it possible to pass
> shared_ptr<>s across exe/dll boundaries (that use different heaps.)

Most times I'm sure you're right. I'm mostly concerned with the cases 
where the cases where the data members of the pointed-to object are all 
simple types, requiring no destructor calls, or ones with similarly 
simple inline destructors; then the C++ implementation can completely 
optimize away function calls except for the deallocation. I suspect 
that the layer of indirection here will make it much more unlikely for 
compilers to perform that optimization.

With shared_ptr's being a commonly recommended way for dynamically 
storing things in vectors without copying the data, I think this may 
occur fairly often. Just looking over my personal code, I have several 
examples of such vectors. It just seems a violation of the 
no-use-no-pay rule.

George Heintzelman
georgeh_at_[hidden]