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Subject: Re: [boost] [atomic] comments
From: Tim Blechmann (tim_at_[hidden])
Date: 2011-10-31 18:30:19

> > > I think, having a mutex per atomic instance is an overkill. However,
> > > a
> > > spinlock per instance might just be the silver bullet. The size
> > > overhead should be quite modest (1 to 4 bytes, I presume) and the
> > > performance would still be decent. After all, atomic<> is intended
> > > to be used with relatively small types with simple operations, such
> > > as copying and arithmetics. In other cases it is natural to use
> > > explicit mutexes, and we could emphasise it in the docs.
> >
> > might be possible, the problem is that this assumes that there is
> > atomic<something> available -- as soon as you hit a platform where
> > everything hits the fallback, you just have to use a mutex and the cost
> > becomes unbearable
> True. But are there realistic platforms without any support of atomic ops
> whatsoever today? If there are, I'm not sure the library should support
> these platforms in the first place.

well, it is quite a chicken-and-egg problem, we need atomics to implement
atomics to implement atomics, when atomics are not available. but in the real
world i guess all platforms will provide some kind of atomic operations, which
are sufficient to implement basic spinlocks.

it would also be fine with me to delegate the implementation to
boost::detail::spinlock in the smart_ptr library (assuming that it will never
be implemented via atomic<>)

cheers, tim

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