Re: [Boost-users] optional_shared_ptr or shared_lazy_ptr extension

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2007-01-11 13:44:46

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On Thu, January 11, 2007 19:41, Ovanes Markarian wrote:
> Hello all,
>
> after some time spent for evaluating the possible scenarios I came up with the following idea.
> Design of a type wrapper similar to functionality offered by boost:shared_ptr and boost:optional.
> Let me try to explain the requirements:
>
>
> 1. The new type must model pointer semantics to wrapped type.
> 2. It must be refernece countable and multi-thread safe in regards of shared operations (copy
> etc.) as it is the case with shared_ptr
> 3. It should be able to create the wrapped type on first non-const member access request, which
> assumes a multi-thread safe operation (when shared accross multiple threads)
> 4. It should support InPlace factory and custom deleter types
> 5. It should not pre-allocate the storage for the contained type
> 6. It should be possible to use static_pointer_cast, dynamic_pointer_cast and const_pointer_cast
> operations with the new type.
>
> Why is optional not an option for me:
> 1. It preallocates memory, which I would like to save and allocate at first request only
> 2. The type should not implement deep copy semantics for the contained value type if copied, but
> act much like a shared_ptr (shallow copy)
>
>
> The most important use case:
>
> class A;
>
> Main Thread
> lazy_ptr<A>   ptr;
>
>
> Thread 1    | Thread 2           | Thread 3
> ------------+--------------------+-------------
> copy of ptr | copy of ptr        | copy of ptr  (use_count == 4, get()const returns NULL)
>             | ptr.get()non-const |              (use_count == 4, get()non-c will return valid A*)
> use(*ptr)   |                    | use(*ptr)    (using the same instance as created from Thread 2)
>
> If dealing intensively with big size data structures this approach can save a lot of memory if
> none of the threads needs an instance.
>
>
>
> All comments are highly appreciated. I also posted some comments on the similar issue, but got a
> suggestion to use boost::optional. Since I was not aware of all the requirements at that time I
> could not go ahead with a discussion.
>
>
>
> With Kind Regards,
>
> Ovanes Markarian
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>

With Kind Regards,

Ovanes