为什么不能在另一个线程上创建 glfw window？

Question

Yes I know opengl is not thread safe but what I want is run a new window with opengl in it on a different thread entirely without doing any sort of data manipulation over opengl and causing weird bugs what i want is have a web server that based on requests sent run a opengl thread render it then save it to a picture (basically im trying to render 3d virtual avatars for a website). But I kept getting this error:

OpenTK.Windowing.GraphicsLibraryFramework.GLFWException: GLFW can only be called from the main thread!

Code being (Licensed under public domain):

public async Task RenderAvatar() {
    while(true) {
        HttpListenerContext td = await httpServer.GetContextAsync();
        HttpListenerRequest req = td.Request;
        HttpListenerResponse res = td.Response;
        if(req.HttpMethod == "GET") {
            if(req.Url.AbsolutePath.ToString() == "/renderAvatar.3d") {
                var parameters = HttpUtility.ParseQueryString(req.Url.Query);
                if(parameters.Count == 3) {
                    var pant = parameters[0].ToString();
                    var face = parameters[1].ToString();
                    var shirt = parameters[2].ToString();
                    Game game = new Game(new string[]{pant,face,shirt, null},new string[]{        "head",
                    "neck",
                    "torso",
                    "larm",
                    "rarm",
                    "lleg",
                    "rleg",null});
                    game.Run();                        
                }
            }
        }
    }

after accessing the web page exception throws but I'm pretty sure it should run fine in theory since I do not do any sort of access other than initializing game type: GameWindow object with parameters taken from the query and running it. So I want to know what is the technical reason behind glfw don't letting me to run it on a different thread even if it will work fine in theory? If it will run fine as long as I don't do data manipulation from different thread Is theres a way to bypass the exception or can I avoid the error by Compiling OpenTK myself and removing the exception and expect it to run fine?

Answer 1

Most GLFW functions, including glfwCreateWindow must by called from the main thread. It says exactly that in the main GLFW reference and the OpenTK reference .

OpenGL is not GLFW. The GLFW thread rules apply to GLFW functions, and so you must respect them while calling GLFW functions. If you want to run OpenGL code in a non main thread, that is all fine.

Importantly, glfwMakeContextCurrent may be called from any thread. This means that you can make a window on the main thread, hand it off to a second thread, and the second thread can then use the OpenGL context of that window. The second thread can also call glfwSwapBuffers , but various other window functions like glfwPollEvents still must be called from the main thread.

If you are ever unsure about the thread safety of a GLFW function, check the reference and it will tell you: https://www.glfw.org/docs/3.3/modules.html