Function createContextByGpuIdx

gpu.hpp:888–975

* @brief Factory function to create a GPU context, which aggregates WebGPU API * handles to interact with the GPU including the instance, adapter, device, and * queue. * * The function takes gpu index to support for multi GPUs. * To activate this function, it needs not only webgpu's headers but also DAWN's headers. * * If dawn is used, it also sets up an error callback for device loss. *

 * @endcode
 */
inline Context createContextByGpuIdx(int gpuIdx,
				     const WGPUInstanceDescriptor &desc = {},
				     const WGPUDeviceDescriptor &devDescriptor = {}) {
  Context context;
  {
#ifdef __EMSCRIPTEN__
    // Emscripten does not support the instance descriptor
    // and throws an assertion error if it is not nullptr.
    context.instance = wgpuCreateInstance(nullptr);
#else
    context.instance = wgpuCreateInstance(&desc);
#endif
    // check status
    check(context.instance, "Initialize WebGPU", __FILE__, __LINE__);
  }

  LOG(kDefLog, kInfo, "Requesting adapter");
  {
    std::vector<dawn::native::Adapter> adapters =
      dawn::native::Instance(reinterpret_cast<dawn::native::InstanceBase*>(context.instance))
      .EnumerateAdapters();
    LOG(kDefLog, kInfo, "The number of GPUs=%d\n", adapters.size());
    // Note: Second gpu is not available on Macos, but the number of GPUs is 2 on Macos.
    //       Calling wgpuAdapterGetInfo function for the second gpu becomes segfault.
    //       When you check all GPUs on linux, uncomment out following codes.
    //
    // for (size_t i = 0; i < adapters.size(); i++) {
    //   WGPUAdapterInfo info {};
    //   auto ptr = adapters[i].Get();
    //   if (ptr && adapters[i]) {
    //     wgpuAdapterGetInfo(ptr, &info);
    //     LOG(kDefLog, kInfo, "GPU(Adapter)[%d] = %s\n", i, info.description);
    //     wgpuAdapterInfoFreeMembers(info);
    //   } 
    // }

    {
      LOG(kDefLog, kInfo, "Use GPU(Adapter)[%d]\n", gpuIdx);
      auto ptr = adapters[gpuIdx].Get();
      if (ptr) {
	WGPUAdapterInfo info {};
	wgpuAdapterGetInfo(ptr, &info);
	LOG(kDefLog, kInfo, "GPU(Adapter)[%d] = %s\n", gpuIdx, info.description);
	wgpuAdapterInfoFreeMembers(info);
      } 
      context.adapter = adapters[gpuIdx].Get();
      dawn::native::GetProcs().adapterAddRef(context.adapter);
    }
  }

  LOG(kDefLog, kInfo, "Requesting device");
  {
    struct DeviceData {
      WGPUDevice device = nullptr;
      bool requestEnded = false;
    };
    DeviceData devData;
    auto onDeviceRequestEnded = [](WGPURequestDeviceStatus status,