Interlocked ops vs XXX::atomic on Win32

Question

What are the advantages and disadvantages of using Interlocked winapi functions instead of any library provides atomic operations on Win32 platform?

Portability is not an issue.

score 4 · Accepted Answer · edited May 23 '17 at 10:33

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If portability is not a concern then you're basically down to deciding whom you trust more to get this right. A library is generally designed to provide portability. It otherwise has a tough time competing with an OS provided implementation that's been battle-hardened for over 15 years.

Check this thread to see an example of how the obvious implementation is not in fact the best.

edited May 23 '17 at 10:33

Community

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answered Nov 26 '10 at 14:51

Hans Passant

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Well, for example, there is TBB::atomic of Intel. Microsoft provides OS, but, Intel produces the processor. Who would you trust more? – ali_bahoo Nov 26 '10 at 15:15
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Hehe, do you trust Intel code to run well on an AMD processor? – Hans Passant Nov 26 '10 at 15:25
Let's assume that the code will always be running on Intel processor which is true in my case. – ali_bahoo Nov 26 '10 at 15:44

score 2 · Answer 2 · answered Nov 26 '10 at 14:17

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The Interlocked winapi functions work on old processors even when there is no CPU support for locked operations. 386 and maybe 486, not really a issue today unless you still support Win9x and older NT.

answered Nov 26 '10 at 14:17

Anders

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They work *differently* on those CPUs though. (they're only atomic with respect to other interlocked operations) – jalf Nov 26 '10 at 15:47

score 0 · Answer 3 · answered Nov 26 '10 at 14:19

It would likely depend up on the specific atomic library in question.

A good library with a specific back-end would likely end up with the same implementation of a couple of ASM instructions to issue an x86 lock instruction and do their work. And assuming the library itself is portable, subsequently make your code portable.

A naive atomic implementation might do something heavier like use a mutex to protect a normal variable. I don't know of any that do - just making the point for argument.

As such, given your stated non-portability requirements, using the Win32 functions should be fine. Alternately, go ahead with an Atomic version, but perhaps look at the actual implementation.

Interlocked ops vs XXX::atomic on Win32

3 Answers3