Re: [boost] Re: bald singleton pointers

From: Jason Hise (chaos_at_[hidden])
Date: 2005-02-13 16:41:53

Pavel Vozenilek wrote:

>"Dave Handley" wrote:
>
>[bald pointer out of singleton]
>  
>
>>The only instance that I can think of where you may want to do this is in 
>>a multi-threaded environment.  And even then only in a very specific set 
>>of circumstances.  Specifically, you may want to do this when you don't 
>>want the overhead of a lock, but, for some other reason, you can 
>>absolutely guarantee that concurrent access to the object (or parts of the 
>>object you are accessing) is valid.  If I'm honest though, I'm having some 
>>difficulty convincing myself that something like this would actually 
>>genuinely be useful.  Perhaps if you could get a "bald pointer" through a 
>>protected member, that was therefore only accessible to derived classes 
>>(hence the singletons themselves).  This could be useful to build into a 
>>static access function that provided a safe pointer, but perhaps without 
>>the overhead of a lock?
>>
>>    
>>
>The use case is a legacy code that accepts only bald pointer.
>
>A singleton may have function unsafe_get().  The object would be
>instantiated if not already.
>
>Code using its result will promise not to destroy given object.
>
>/Pavel
>
In such cases, I wonder if it might be best for the user's singleton to 
provide the function:

class Example : public singleton < Example >
{
// protected ctor and dtor
public:
    Example * unsafe_get (  )
    {
        return this;
    }
};

That way not all singleons would need to suffer the 'security hole' just 
because a few need it.

-Jason