LDC optimized builds causing unexpected behaviour when sharing variable between threads

[Keivan Shah]

On Wednesday, 1 June 2022 at 08:23:18 UTC, Johan wrote:
> This is not a bug.
> The solution with `volatileLoad` works, but I think it 
> technically isn't quite correct; documentation says: "They 
> should not be used for communication between threads.".
>
> There are many articles online about this kind of conditional 
> loop on a variable that is modified by another thread. For 
> example: 
> https://stackoverflow.com/questions/10091112/using-a-global-variable-to-control-a-while-loop-in-a-separate-thread  and  https://devblogs.microsoft.com/oldnewthing/20180924-00/?p=99805
>
> -Johan

Hey Johan,
Thanks for the quick response. As you mentioned even I don't feel 
the solution with `volatileLoad` is correct and so was looking 
for something else. The 
[documentation](https://dlang.org/articles/migrate-to-shared.html#shared) stated that

> Global data that is meant to be shared among multiple threads 
> should be marked with the shared keyword

So to me it seemed like marking the variable as `shared` should 
have made it accessible as well as it takes care of the memory 
ordering. That plus the fact that the snippet works in `dmd` but 
not `ldc` made me think it maybe was a bug. Anyways, have gotten 
a better understanding of the issue now, probably will use 
[core.atomic.atomicFence](https://dlang.org/phobos/core_atomic.html#.atomicFence) to ensure the memoryOrdering.

Thanks and Regards,
Keivan Shah.