Re: [Boost-users] [signals2] tracking intrusively ref-counted object

Subject: Re: [Boost-users] [signals2] tracking intrusively ref-counted object
From: Frank Mori Hess (fmhess_at_[hidden])
Date: 2009-09-06 09:52:52

On Sunday 06 September 2009, Igor R wrote:
> Actually, you mean I have to override object's release() method -- as
> this's the only piece of code that knows when ref.count drops to 1.
> I'm still not sure I understand how to make this solution thread-safe.
> Lets consider the following scheme:
>
> struct object
> {
>   void init()
>   {
>     selfAncor_ = some_intrusive_ptr<object>(this);
>     connection1_ = signal1_.connect(&handle, ref(selfAncor_));
>     connection2_ = signal2_.connect(&handle, ref(selfAncor_));

No, you want to bind a copy of the smart pointer to the slot by value.  
Making the slot accept it by reference just avoids creating another 
temporary copy during invocation, which makes the reference counting more 
complicated.

>   }
>
>   int release()
>   {
>     do_release();
>     if (refcount_ == 1)
>     {
>       connection1_.disconnect();
>       connection2_.disconnect();
>       // the following line is unsafe, because some slot invocation
> might be in progress!
>       selfAncor_.reset();

No, there's still a copy bound to the slot which won't be destroyed until 
the invocation is finished and the signal garbage collects the 
disconnected slot from its slot list.

>     }
>   }