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0 pointsasveikau11y ago0 comments

Well, it looks like Apple named this particular API "OS atomics", a name which makes me cringe a bit.

But, a few points:

1. There is historically a distinction between "operating system" and "shared library shipping with the operating system". I think I am losing this battle though.

2. On a number of platforms (not sure if Apple's "OS atomics" concept counts here), the atomic wrappers are not even functions in a shared library. They may be declared inline in a header file. Or they may be compiler intrinsics, where the compiler doesn't generate any function call in any circumstances. Is that an "OS function"? Not really.

In either case #1 or case #2, I think "OS atomics" is a dumb name. We are really talking about CPU features, not OS features. If it doesn't generate a trap into kernel mode that doesn't very much sound like the OS doing the work.

Calling it "the OS" sounds more like a fundamental misunderstanding of dynamic linking and what it is. I hear so many variants of this core misunderstanding all over the place. Thinking that spinlocks need kernel help is one such manifestation.

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mikeash11y ago

#1 sounds like a pretty minority viewpoint. OSes these days are a lot more than just the kernel and things that call into the kernel. If you do a fresh install of the OS then I think what you find on the disk afterwards can all be reasonably referred to as "the OS."

#2 does not apply here. This particular API isn't implemented inline, or with compiler intrinsics, or assembly. They're actual calls.

If you're talking about the general concept of atomics, then I agree that "OS atomics" is a dumb name. But we're not talking about that. We're talking about a specific API that happens to implement that general concept. That specific API is part of the OS.

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