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0 pointsgreatfilter2512y ago0 comments

> how can we provide a mutual exclusion mechanism on the bare hardware?

This is a bit misleading. It's easier to provide mutual exclusion on bare hardware than in an OS; just do a spinlock, except with modern ISAs the core doesn't even spin.

Presumably core doesn't offer this because it's a massive footgun for devs new to multithreading who would not understand why this is unacceptable to use in an OS-hosted process.

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tialaramex2y ago

> with modern ISAs the core doesn't even spin.

Although tricks like PAUSE are much cheaper than a naive spinlock, they are still spinning as I understand it, just not as frantically because that's pointless and wasteful.

dataangel2y ago

It's even simpler than that, PAUSE just prevents the CPU from trying to speculatively execute across iterations.

greatfilter251OP2y ago

I'm not familiar with a pause instruction in a modern isa. Sounds like x86 crap.

I'm talking about wfi, wfe, and friends.

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