[llvm-dev] [RFC] [lld] Replace use of 'concurrency::parallel_for_each' with standard library

[Rafael Avila de Espindola via llvm-dev]

Thank you so much for tracking down such a tricky issue.

I agree that we should disable it. Should we just delete the ifdefs? We
could in theory disable it just for debug builds, but that could create
some hard to reproduce bugs.

Cheers,
Rafael

Owen Reynolds via llvm-dev <llvm-dev at lists.llvm.org> writes:

> Hello all,
>
> Last year I submitted a bug regarding the use of 'parallel_for_each' and
> Windows Concurrency Library. We have found that when compiling in Visual
> Studio 2015 and 2017 with /MTd, the use of 'concurrency::parallel_for_each'
> can cause unhandled exceptions when the program is exiting.
>
> https://bugs.llvm.org/show_bug.cgi?id=34976
>
> After having some difficulty clarifying this issue with Microsoft I
> submitted the issue again this week and have found that they are aware of
> the problem. However, I've yet to be given any information on a timescale
> for a fix.
>
> https://developercommunity.visualstudio.com/content/problem/198027/use-of-concurrencyparallel-for-each-with-the-multi.html
>
> For our team this bug has caused problems when testing LLD. We suggest the
> removal of this MSVC specific functionality in "llvm::parallel" until a fix
> is made or alternative found. This could be easily swapped to use the
> existing standard library implementation in the meantime.
>
> Owen Reynolds
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