Thread: Atomic operations

  1. #1
    Registered User
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    May 2008

    Atomic operations


    I'm reading some of the C++ working standard, and I arrive at the chapter on Atomic Operations Library.

    Are these types/operations which will never be split over various threads, i.e., thread-safe types and operations?

    If that's true, why are there types like "atomic_bool" ? A normal primitive 'bool' is already type safe?

    Further, could someone explain me some of the applications? Massive parallel for example?

    Thanks for your explications!!!


  2. #2
    and the hat of int overfl Salem's Avatar
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    Aug 2001
    The edge of the known universe
    Being type-safe and thread-safe are completely different concepts.

    > Further, could someone explain me some of the applications?
    Anything involving threads.
    On a single CPU, the granularity is a single instruction.
    On a multi-CPU system, the granularity is a bus cycle.

    What the atomic types guarantee is that the objects will still do the right thing, despite the increased opportunity for interleaving the actions of multiple CPUs.
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  3. #3
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    Jun 2005
    Quote Originally Posted by Salem View Post
    On a single CPU, the granularity is a single instruction.
    That's no longer true with multi-core CPUs.

  4. #4
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    I'd say that "single CPU" means "Single core" - Multi-CPU systems are those with more than one processing unit, no matter if that is provided through a single chip or multiple chips.

    Note that for example a single-core CPU with an "intelligent"[1] graphics processor, is also a "multiprocessor" system. Although it is of course only relevant for data shared between the CPU and the GPU.

    [1] Literally anything more advanced than the VGA graphics adapters, and certainly ALL of the 3D graphics cards are "intelligent" in this context.

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