SPIN | 12 key , 3 encoder USB-C Macro Pad | Change Data Capture library

std::memory_order_acq_rel is not required.

Mutex synchronization is between 2 threads.. one releasing the data and another acquiring it.
As such, it is irrelevant for other threads to perform a release or acquire operation.

Perhaps it is more intuitive (and efficient) if the acquire is handled by a standalone fence:

Reading a memory address does not clear the cache line.

Writing does.

So in a modern computer, there is RAM, and there are multiple layers of cache "around" the CPU (they are called L1, L2 and L3 cache, but the important part is that they are layers, and the CPU is at the middle). In a multi-core system, often the outer layers are shared; the innermost layer is usually not, and is specific to a given CPU.

Clearing the cache line means informing every other cache holding this memory "the data you own may be stale, throw it out".

Test and set writes true and atomically returns the old value. It clears the cache line, because it writes.

Test does not write. If you have another thread unsynchronized with this one, it reading the cache of this memory doesn't have to be poked.

The outer loop writes true, and exits if it replaced false. The inner loop waits until there is a false visible, then falls to outer loop. The inner loop need not clear every other cpu's cache status of the value of the atomic flag, but the outer has to (as it could change the false to true). As spinning could go on for a while, avoiding continuous cache clearing seems like a good idea.

I had to dig into the Rust repository history to get to this answer:

The yield has been replaced with isb in c064b6560b7c:

On arm64 we have seen on several databases that ISB (instruction synchronization barrier) is better to use than yield in a spin loop. The yield instruction is a nop. The isb instruction puts the processor to sleep for some short time. isb is a good equivalent to the pause instruction on x86.

[...]

So essentially, it uses the time it takes for an ISB to complete to pause the processor, so that it wastes less power.

Peter Cordes explained it nicely in one of his comments:

ISB SY doesn't stall for long, just saves a bit of power vs. spamming loads in a tight loop.

Your question isn't super clear about where you get these instances, so I'm guessing a bit.

Try some SQL like this to avoid race conditions. Be sure to use MySQL's InnoDB storage engine; MyISAM and AriaDB don't support transactions.

I fixed it! Unfortunately, the solution was pretty specific to my situation so it may not provide too much value for others. Although, I hope it helps with troubleshooting.

After locally switching my backend configuration over to her site using amplify pull --appId --envName I noticed that the configuration call was now successful. I had forgotten that I had never actually run her site locally, I only hopped to her branch to merge and push.

The site was still not rendering though, which perked my ears for a race condition. I discovered that I had left a checker for some images that was gating render of my topmost component. My wife has a ton of images, so I think this call was taking too long to make the chain of events load items in the correct order, and the page showed blank. Simply removing that check for those images at that point, showed the UI.

it does not need a proxy

Did you try using the in operator?

You need add a transparent hole in .curtain class:

Multiple threads may compete to do this (see "initialization race" comment).

To paraphrase the code: