Re: [boost] [SmartPtr] alternative to enable_shared_from_this

Subject: Re: [boost] [SmartPtr] alternative to enable_shared_from_this
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2017-01-16 02:24:24

On 6/01/2017 06:50, Roberto Hinz wrote:
> hmm, I didn't know enable_shared_from_raw until now. Still, can
> shared_handle be an alternative to enable_shared_from_raw ?
>
> enable_shared_from_raw has been criticized of been too prone to cause
> memory leaks [1] .
>
> [1]
> http://stackoverflow.com/questions/22184772/why-is-boostenable-shared-from-raw-so-undocumented

The point there is that if you inherit enable_shared_from_raw and then 
provide some way to obtain a non-shared pointer to the object (ie. you 
don't use something like the shared factory pattern to guarantee that 
the object can't be constructed without a shared_ptr) then it will leak 
memory if you do so.  (In much the same way that setting up a pointer 
cycle will leak memory, except on a smaller scale.)

Conversely, if you inherit enable_shared_from_this and similarly provide 
some way to obtain a non-shared pointer to the object, then calling any 
method that assumes that there is a shared pointer (by calling 
shared_from_this()) will throw bad_weak_ptr.  [Or in some older 
versions, is undefined behaviour instead.]

Both of them result from misusing the types and both [now] have 
well-defined misbehaviours that result from doing so.  You get to decide 
which misbehaviour you prefer.  But both are also easily avoided by 
using factories.