cannot build without thread API

[pca006132]

cannot build without thread API

[brycelelbach]

Okay give this a shot please: -D_LIBCUDACXX_HAS_THREAD_API_EXTERNAL -D_LIBCUDACXX_HAS_THREAD_API_CUDA

[elalish]

This is looking more like a blocker, since even when enabling -pthread in emscripten, we still get Thrust's No Thread API error. So perhaps there is an additional bug regarding detecting pthread support in the emscripten compiler?

Still, considering all the complexities of using pthreads in WASM, especially since we require ALLOW_MEMORY_GROWTH, the better option would still be to simply not require the thread API at all for the serial backend.

[brycelelbach]

I think this actually an issue with https://github.com/NVIDIA/libcudacxx, not Thrust.

[brycelelbach]

Can you send us the specific compilation error you're getting?

Can you try defining -D_LIBCUDACXX_HAS_NO_THREADS and see if that helps?

[elalish]

The original error:

/Users/elalish/Code/manifold/src/third_party/thrust/dependencies/libcudacxx/include/cuda/std/detail/libcxx/include/__config:1559:6: error: "No thread API"

With your define I get:

/Users/elalish/Code/manifold/src/third_party/thrust/dependencies/libcudacxx/include/cuda/std/detail/libcxx/include/__config:1584:2: error: _LIBCUDACXX_HAS_NO_THREADS cannot be set when __STDCPP_THREADS__ is set.

The compile command that generates the error is:

/opt/homebrew/Cellar/emscripten/3.1.31/libexec/em++ @CMakeFiles/collider.dir/includes_CXX.rsp -O3 -DNDEBUG -Werror -Wall -Wno-sign-compare -Wno-unused -fexceptions -DTHRUST_DEVICE_SYSTEM=THRUST_DEVICE_SYSTEM_CPP -std=gnu++17 -MD -MT src/collider/CMakeFiles/collider.dir/src/collider.cpp.o -MF CMakeFiles/collider.dir/src/collider.cpp.o.d -o CMakeFiles/collider.dir/src/collider.cpp.o -c /Users/elalish/Code/manifold/src/collider/src/collider.cpp

[elalish]

Excellent, that worked! Thank you. Quite the magical incantation.

[brycelelbach]

Is there a macro that Emscripten defines that we can use to detect the Emscripten environment? If so, then we can do this automatically.

[elalish]

Looks like it's __EMSCRIPTEN__: https://emscripten.org/docs/compiling/Building-Projects.html#detecting-emscripten-in-preprocessor

[brycelelbach]

I've created a PR to fix this in libcu++. Can you confirm that the issue is fixed once you define those two macros? Nothing else blows up?

[elalish]

Our tests are now passing our CI on a bunch of different systems, so I think it's good. We just added those defines for the emscripten build.