[extropy]

How about a new opcode wait till memory address read equals? That would allow implementing a power efficient spinlock.

Oh there is one already. Meet PAUSE: https://www.felixcloutier.com/x86/pause

Edit: related post from 2018 https://news.ycombinator.com/item?id=17336853

[dbaupp]

The benchmarked spin-locks are using it, via https://doc.rust-lang.org/std/sync/atomic/fn.spin_loop_hint....

Implementation: https://doc.rust-lang.org/src/core/hint.rs.html#64-93

[jnordwick]

MONITOR/MWAIT will get you the part where a thread will pause and the cpu can rest until a write on a store on an address range, then the waiting thread is allowed to continue. You can't wait on a specific value though.