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Subject: Re: [boost] storing intrusive_ptr in atomic?!
From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2013-10-25 05:08:42

On Fri, Oct 25, 2013 at 9:11 AM, Oliver Kowalke <oliver.kowalke_at_[hidden]>wrote:

> 2013/10/25 Andrey Semashev <andrey.semashev_at_[hidden]>
> > intrusive_ptr is not trivial-copyable, precisely because it has to
> operate
> > on
> > the counter. Using memcpy for copying it is not correct.
> >
> For this reason it is
> > not compatible with atomic<>. You have to use raw pointers with atomic<>.
> >
> I don't agree because the standard told us:
> 1.) 'For any object of trivially copyable type T, whether or not the
> object
> holds a valid value of type T, the underlying bytes making up the object
> can be copied into an array
> of char or unsigned char. If the content of the array of char or unsigned
> char is copied back into the
> object, the object shall subsequently hold its original value.'

> 2.) 'For any trivially copyable type T, if two pointers to T point to
> distinct T objects obj1 and obj2, where
> neither obj1 nor obj2 is a base-class subobject, if the underlying bytes
> (1.7) making up obj1 are copied
> into obj2,41 obj2 shall subsequently hold the same value as obj1.'

Intrusive_ptr doesn't have tivial copy constructor (how could it have? it
needs to update the counter), ergo is not trivially copyable and the above
two point do not apply.

-- gpd

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