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Subject: Re: [boost] Fw: [atomic] review results
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-11-08 07:17:10

Helge Bahmann wrote:
> On Tuesday 08 November 2011 12:30:58 you wrote:
> > > well gcc certainly follows the recommendation of the
> > > standard by making the *lock-free* atomics both address-
> > > free and free from process state, I don't read the standard
> > > as suggesting (or even requiring) anything for emulated
> > > atomics
> >
> > in my reading the sentence `The implementation should not
> > depend on any per- process state' is not restricted to lock-
> > free atomics, but i am not a native speaker and i could be
> > wrong.
> neither am I but from the following full excerpt as quoted by
> Peter Dimov:
> [ Note: Operations that are lock-free should also be address-
> free. That is, atomic operations on the same memory location
> via two different addresses will communicate atomically. The
> implementation should not depend on any per-process state. This
> restriction enables communication by memory that is mapped into
> a process more than once and by memory that is shared between
> two processes. —end note ]
> I think that "address-free" clearly applies only to "lock-
> free", and if something is not "address-free" then the point
> whether it can be used interprocess is kind of moot as it is
> most certainly not going to be mapped at the same address (if
> you consider numerically identical addresses in different
> spaces to be the same at all).

My reading suggests that everything is related to lock-free operations. This is evident in the second sentence, since it begins with "that is", which is introducing clarification of the first sentence. The third sentence is stating a desired goal which is necessary for the sharing described in the last sentence. The question, then, is whether the last two sentences are specifically related to lock-free operations or are intended to apply more generally. While there is room for another interpretation and contrary intention, the fact that this is structured as a single note suggests it is a cohesive discussion all related to the thesis statement in the first sentence. I, therefore, conclude that the entire note is about lock-free operations.

Since there is confusion, it would be appropriate to file a DR on the note to get clarity. However, since it is non-binding text, I'm not sure how the committee will handle it.

Rob Stewart robert.stewart_at_[hidden]
Software Engineer using std::disclaimer;
Dev Tools & Components
Susquehanna International Group, LLP


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