Add util/atomic.h

[ghaug]

Hi,
I had the problem that I wanted to check a library modified by me which in turn includes a library that includes util/atomic.h and that doesn't work, of course. I added a mocked version of util/atomic.h, that simply does nothing. Atomicity by switching off interrupts is not possible on the host OS but timing behavior will differ anyway, therefore I think this approach is acceptable.
Best,
Gunter

[ianfixes]

Hi Gunter, thanks for submitting this!

Can you add (or just post here) a dummy/example usage of some atomic.h functions that we could refer to in a unit test? That way, we have a guard against future edits breaking things unexpectedly.

[ghaug]

Hi Ian,
thanks for the quick reply! There are two macros defined in atomic.h that can be used, namely ATOMIC_BLOCK and NONATOMIC_BLOCK. Each uses one of two parameters. An example would be:

ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
int a = callSomeFunction(para);
passToSomeOtherFunktion(a);
}

ATOMIC_BLOCK takes either ATOMIC_RESTORESTATE or ATOMIC_FORCEON as parameter, while NONATOMIC_BLOCK takes either NONATOMIC_RESTORESTATE or NONATOMIC_FORCEOFF, so there are just four combinations in total.

One more thing: Two of the checks fail for my pull request. I'm new to this project and I don't really know what's wrong.

[ghaug]

Where would a unit test go? Would arduino_ci/SampleProjects/TestSomething/ be the right place?

[ianfixes]

Regarding the test failures, I think you can ignore the one with the linter -- it looks like a temporary problem with GitHub (and if not, I can look into it later). The only problem I'm seeing is a spelling error: https://github.com/Arduino-CI/arduino_ci/actions/runs/4424323994/jobs/7765538401?pr=350#step:4:19

Regarding a unit test, that would be awesome! Please call it something like atomic.cpp and put it in SampleProjects/TestSomething/test. For the format, just follow an example like the minimal ones shown in null.cpp or check the docs: https://github.com/Arduino-CI/arduino_ci/blob/master/REFERENCE.md#most-basic-unit-test

[ghaug]

I've added a unit test. As the macros don't do anything on the host, it just checks that all the four combinations compile without errors.

[ianfixes]

This is excellent, thank you!