Re: [Boost-users] Casting a shared_ptr as a prototyped (void *)?

From: Elli Barasch (comptonsw_at_[hidden])
Date: 2008-01-16 09:06:43

Agreed, sending a raw pointer leaves that window open.  Hence my 
question about "new"ing onto the stack.

Cheers,
Elli

Leon Mlakar wrote:
>  
> Wouldn't that open a potential gap for original shared_ptr to 
> destroy whatever is pointed to by raw pointer before thread manages to 
> bind it back to the shared count?
> .
>  
> Cheers,
>  
> Leon
>
>     ------------------------------------------------------------------------
>     *From:* boost-users-bounces_at_[hidden]
>     [mailto:boost-users-bounces_at_[hidden]] *On Behalf Of *Ovanes
>     Markarian
>     *Sent:* Wednesday, January 16, 2008 8:31 AM
>     *To:* boost-users_at_[hidden]
>     *Subject:* Re: [Boost-users] Casting a shared_ptr as a prototyped
>     (void *)?
>
>     Try using the enable_shared_from_this idiom:
>     http://www.boost.org/libs/smart_ptr/sp_techniques.html#from_this
>
>     This will allow you to pass a raw pointer to your thread and later
>     on bind the raw pointer to the correct shared counter.
>
>
>     Good Luck,
>     Ovanes
>
>
>     On Jan 16, 2008 6:45 AM, Elli Barasch <comptonsw_at_[hidden]
>     <mailto:comptonsw_at_[hidden]>> wrote:
>
>         Richard Dingwall wrote:
>>         On Jan 16, 2008 5:22 PM, Elli Barasch <comptonsw_at_[hidden]> <mailto:comptonsw_at_[hidden]> wrote:
>>           
>>>          Richard Dingwall wrote:
>>>
>>>          On Jan 16, 2008 1:11 PM, Elli Barasch <comptonsw_at_[hidden]> <mailto:comptonsw_at_[hidden]> wrote:
>>>
>>>
>>>          I'd like to pass a shared_ptr as the entry argument to a thread function
>>>         via pthread_create. However,
>>>         the entry argument is prototyped as void *. I can't simply cast the
>>>         shared pointer as a (void *). How do I go about this?
>>>
>>>          Try passing:
>>>
>>>         static_cast<void *>(your_ptr.get())
>>>
>>>
>>>         Richard
>>>         _______________________________________________
>>>         Boost-users mailing list
>>>
>>>         Boost-users_at_[hidden] <mailto:Boost-users_at_[hidden]>
>>>         http://lists.boost.org/mailman/listinfo.cgi/boost-users
>>>
>>>
>>>          A follow up question.  Does get() increase the reference count, or does it
>>>         simply return the underlying pointer without doing so?  If so, I'd be
>>>         worried that a race exists such that the object could be destroyed before
>>>         the thread gets to run.
>>>             
>>         get() does not incremement the reference count, as it returns a raw
>>         pointer, and there is no way of knowing how a raw pointer is being
>>         consumed or stored.
>>
>>         If you the function you are passing it to retains a reference to the
>>         pointer anywhere, there is no way this can be tracked by the
>>         shared_ptr. Furthermore, if the shared_ptr(s) go out of scope the raw
>>         pointer references will be left dangling.
>>
>>         HTH,
>>
>>         Richard
>>         _______________________________________________
>>         Boost-users mailing list
>>         Boost-users_at_[hidden] <mailto:Boost-users_at_[hidden]>
>>         http://lists.boost.org/mailman/listinfo.cgi/boost-users
>>
>>           
>         Is there a way I can "new" a copy of the shared_ptr onto the
>         stack?  Something like:
>
>         pthread_create(&t,&attr,&func,(void *) new
>         shared_ptr<T>(shp));    //mangled syntax, I know
>
>         Something like this would guarantee the object stays in scope?
>
>
>
>
>
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>         Boost-users_at_[hidden] <mailto:Boost-users_at_[hidden]>
>         http://lists.boost.org/mailman/listinfo.cgi/boost-users
>
>
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