problem with GL commands that run in pthread and they has dependency with each other

[aharondavid]

Hi,
please have a look on the following pseudo code:
it illustrate a real problem when you try to use GL in thread and main thread.
any idea how to solve it will be welcome.

Thread()
{
    //emscripten  post those commands  to the main thread by emscripten_sync_run_in_main_runtime_thread
    
    //drawing on canvas.
    glBindTexture(bind1);   
    glTexImage2D(tex1)
};

main_thread()
{
    createThread(Thread); //create a pthread

    //do somthing
   
    usleep(1);   //here, the busy wait mechanize is  executed

    //drawing on canvas.
    glBindTexture(bind2);
    glTexImage2D(tex2)
}

possible execution:

1. Thread run glBindTexture(bind1) , this command, internally, post and insert the glBindTexture to the main thread queue by emscripten_sync_run_in_main_runtime_thread
2. main thread run usleep that do busy wait
3. busy wait is going to the main thread queue and exeute glBindTexture(bind1) that was inserted to the queue by step 1.
4. main_thread execute glBindTexture(bind2);
5. Thread run glTexImage2D(tex1), but it is work on bind2 insted of bind 1 !!!!

[sbc100]

Seems like this is general GL problem maybe? See https://stackoverflow.com/questions/22574879/using-the-same-opengl-context-in-multiple-threads

[sbc100]

Also: https://developer.apple.com/library/archive/documentation/GraphicsImaging/Conceptual/OpenGL-MacProgGuide/opengl_threading/opengl_threading.html#:~:text=OpenGL%20Restricts%20Each%20Context%20to%20a%20Single%20Thread,-Each%20thread%20in&text=If%20you%20modify%20the%20same,or%20it%20might%20render%20improperly.

"OpenGL is not reentrant. If you modify the same context from multiple threads simultaneously, the results are unpredictable. Your application might crash or it might render improperly."

[aharondavid]

the context are create for each thread by emscripten_webgl_create_context.
and the return context is well handled by emscripten code like in webgl1.c .
but, when I more think about that, I don't think that emscriptrn can do something to fix the above code.