[cfe-dev] [clangd] Worker threads stack size

[Alex Lorenz via cfe-dev]

I think the best solution is to use `llvm::llvm_execute_on_thread` instead of `std::thread`.

Cheers,
Alex

> On Aug 17, 2018, at 7:12 AM, Roman Popov via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> In case MacOS LibC++ is implemented on top of pthreads, than you can can use pthreads API to set default stack size. This will probably be miminal possible platform-specific workaround.
> 
> пт, 17 авг. 2018 г. в 6:27, Ilya Biryukov via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>>:
> Would be nice to get around this limitation in the standard library. I don't think we can do it in a standard-compliant way, though.
> There's `llvm::llvm_execute_on_thread`, but it is an OS-specific implementation.
> 
> Are there any ways to set default stack sizes for the newly created threads? Even if it's platform-specific code, it should be pretty localized and we could reuse the STL implementation of threads.
> I don't know of reliable APIs to do that, unfortunately.
> 
> On Fri, Aug 17, 2018 at 2:43 PM Eric Liu <ioeric at google.com <mailto:ioeric at google.com>> wrote:
> +clangd-dev at lists.llvm.org <mailto:clangd-dev at lists.llvm.org> +Ilya Biryukov <mailto:ibiryukov at google.com> 
> 
> On Fri, Aug 17, 2018 at 2:41 PM Dmitry.Kozhevnikov at jetbrains.com <mailto:Dmitry.Kozhevnikov at jetbrains.com> via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
> Hello!
> 
> clangd uses std::thread for spawning worker threads to parse files (see AsyncTaskRunner::runAsync in tools/clang/tools/extra/clangd/Threading.cpp). Unfortunately, std::thread lacks the ability to customize the stack size, and the default one might be insufficient for parsing complex source files. For example, on macOS, the default stack size for non-main threads is 512K, so the following code causes a stack overflow (on my machine) with clangd, while being way below the default constexpr evaluation depth threshold:
> 
>         constexpr int foo(int x) {
>             return x == 1 ? 1 : foo(x - 1) + 1;
>         }
>         static_assert(foo(50) > 0, "");
> 
> This also can be observed on some real-world projects.
> 
> Do I understand correctly that the only way to fix it would be to abandon std::thread and reimplement the platform-specific thread spawning (using pthreads/WinAPI), or is there another solution available in LLVM/clang codebase?
> 
> Best regards,
> Dmitry Kozhevnikov._______________________________________________
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> 
> -- 
> Regards,
> Ilya Biryukov
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