Calling into worker via embind with PROXY_TO_PTHREAD=1 attempts to call GL functions on the main thread

[sasmaster]

Hi.
After not receiveing any answer in the "Issues" list I am asking for help with this problem here.

I am writing a rendering app. I need it to run in a secondary thread in order not to interfere with UI.
My linker config is as follow:

-sINITIAL_MEMORY=134217728 -sMAX_WEBGL_VERSION=2 -sWASM=1 -sFULL_ES3 -sASYNCIFY -sPROXY_TO_PTHREAD=1 -sOFFSCREEN_FRAMEBUFFER=1 -sOFFSCREENCANVAS_SUPPORT=1 -sNO_EXIT_RUNTIME=1 -lembind -sENVIRONMENT=web,worker -sUSE_PTHREADS=1 -sPTHREAD_POOL_SIZE=8 -lpthread -msimd128 -matomics -mbulk-memory

Inside my app I am creating webgl2 context with the following attributes:

attrs.explicitSwapControl =  EM_TRUE;
attrs.renderViaOffscreenBackBuffer = EM_FALSE;
attrs.enableExtensionsByDefault = EM_TRUE;
attrs.premultipliedAlpha = EM_TRUE;
attrs.preserveDrawingBuffer = EM_FALSE;
attrs.proxyContextToMainThread = EMSCRIPTEN_WEBGL_CONTEXT_PROXY_DISALLOW;

I am not sure about the second one but it is probably not related to my problem.
Now, I have a function called Init() and Run(). Init() creates webgl context and makes it current. Run() creates renderable objects and launches render loop with emscripten_set_main_loop_arg(&Render, this, 0, 1);

If Run() gets called within the app, like this:

  int main(int argc, char* argv[])
{
	if(!app.Init())
	{
		return EXIT_FAILURE;
	}
	app.Run();
	return EXIT_SUCCESS;
}

It all works, Stuff is rendering.
However,I need this function to be called via button press on the front end. For this I am using embind to expose the function to JS.
If I call Run() via JS it looks like the webgl context gets lost. Also in the callstack I can see that the code tries to execute the function on the main thread. And my context lives in the worker thread.

WasmApp.js:4923 Uncaught TypeError: Cannot read properties of undefined (reading 'bindFramebuffer')
    at _glBindFramebuffer (http://localhost:5500/WasmApp.js:4923:9)
    at imports.<computed> (http://localhost:5500/WasmApp.js:3042:20)
    at WasmApp.wasm._do_call (http://localhost:5500/WasmApp.wasm:wasm-function[1417]:0x6fd54)
    at WasmApp.wasm.maybe_call_on_current_thread (http://localhost:5500/WasmApp.wasm:wasm-function[1416]:0x6f037)
    at WasmApp.wasm.do_dispatch_to_thread (http://localhost:5500/WasmApp.wasm:wasm-function[1412]:0x6ebd2)
    at WasmApp.wasm.emscripten_async_run_in_main_thread (http://localhost:5500/WasmApp.wasm:wasm-function[1418]:0x71cae)
    at WasmApp.wasm.emscripten_async_run_in_main_runtime_thread_ (http://localhost:5500/WasmApp.wasm:wasm-function[1423]:0x725f7)
    at WasmApp.wasm.glBindFramebuffer (http://localhost:5500/WasmApp.wasm:wasm-function[1260]:0x6172f)
    at WasmApp.wasm.WebApp::Run() (http://localhost:5500/WasmApp.wasm:wasm-function[1238]:0x5f746)
    at WasmApp.wasm.emscripten::internal::MethodInvoker<emscripten::internal::rvp::default_tag, void (WebApp::*)(), void, 

From what I understood in the docs, embind should work fine with worker proxing function calls into the worker thread. But here it doesn't look like that. It seems like embind is attempting to execute the function on the main thread, which is not what I want.
Can someone explain what's going on here? And if embind is not supposed to work in this mode, what is the alternative for setting a communication between this wasm app and JS?
Thanks.

[sbc100]

When you build with -sOFFSCREENCANVAS_SUPPORT it looks like all gl calles (e.g. glBindFramebuffer) are conditionally proxied back to the main thread.

For glBindFramebuffer see

emscripten/system/lib/gl/webgl1.c

Line 133 in 4b76531

ASYNC_GL_FUNCTION_2(EM_FUNC_SIG_VII, void, glBindFramebuffer, GLenum, GLuint);

This definition uses ASYNC_GL_FUNCTION_2 which is defined here:

emscripten/system/lib/gl/webgl_internal.h

Line 26 in 4b76531

#define ASYNC_GL_FUNCTION_2(sig, ret, functionName, t0, t1) ret functionName(t0 p0, t1 p1) { GL_FUNCTION_TRACE(); if (pthread_getspecific(currentThreadOwnsItsWebGLContext)) emscripten_##functionName(p0, p1); else emscripten_async_run_in_main_runtime_thread(sig, &emscripten_##functionName, p0, p1); }

This looks like the function will run on the worker thread if pthread_getspecific(currentThreadOwnsItsWebGLContext) otherwise it will get proxied back to the main thread.

I'm not sure that will solve your problem but it might help you debug?