[browser][MT] Make ChangeLocalTimeZone thread-safe

[mkhamoyan]

Fixes #101166

[ilonatommy]

/azp run runtime-wasm

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ilonatommy]

Locally I cannot reproduce running in the loop.

[pavelsavara]

I think that this is just hiding real underlying issue with emscripten.

It is posting async messages to UI thread from whatever thread exeuted the TZ change. And those messages probably come in random order.

Let's reconsider.

[pavelsavara]

Let's revert this change, because it effectively hides the problem from the test.

Let's rather create additional test which will change TZ from many different threads in threadpool.
And observe the overall impact.
What would be expected behavior on Windows ?

[ilonatommy]

What would be expected behavior on Windows ?

well, change on windows has an effect in the whole system, including registries, so if we do it concurrently I would assume a race and undefined expected result

[pavelsavara]

well, change on windows has an effect in the whole system, including registries, so if we do it concurrently I would assume a race and undefined expected result

You are right, my bad. We should not try to make it work in parallel from multiple threads.

We need to catch one (non-UI) thread doing it and the change being propagated too slowly. So that we can understand how it works in emscripten and what we need to synchronize in Mono. To prevent this "read after write hazard" or whatever it is.

[ilonatommy]

We need to catch one (non-UI) thread doing it

Do I understand it right that we drop the concept of improving test, revert the lock changes and now the goal is to pin debugger and investigate what is the reason for the failure? This failure was hit once per few weeks, any suggestions how to increase the probability of reproduction?

[pavelsavara]

Do I understand it right that we drop the concept of improving test, revert the lock changes

I think so. Current code is how people write TZ code and it's broken only on MT WASM.

now the goal is to pin debugger and investigate what is the reason for the failure?

Yes, I don't expect that you would be able to use debugger.

This failure was hit once per few weeks, any suggestions how to increase the probability of reproduction?

Run it in a loop 1000 times.

[mkhamoyan]

Thanks @pavel and @ilonatommy for clarification.
I left comment under the issue per this discussion and will close this PR.