Taking images from the camera in Thread(worker)

[moondayyy]

I can access the document object with javascript codes in em_asm without a thread, but I cannot access it when I open a thread (i.e. worker).
In this link, it says that I cannot access the "window, document, parent" objects.

What I want to do is to open an infinite loop in the thread and use setInterval?
The video element is taking images from the camera.
Is there an alternative solution?
How can I get an image from the camera in a thread?

CMakeLists.txt:

cmake_minimum_required(VERSION 3.22)
project(emscripten_global_variable_test)
set(CMAKE_CXX_STANDARD 17)
add_executable(emscripten_global_variable_test main.cpp)
set_target_properties(${PROJECT_NAME} PROPERTIES LINK_FLAGS "--bind -sUSE_PTHREADS -sPTHREAD_POOL_SIZE=5 -s TOTAL_MEMORY=256MB -s ALLOW_TABLE_GROWTH=1 -s NO_EXIT_RUNTIME=1 -s ALLOW_MEMORY_GROWTH=1 -O0 -s EXPORT_ALL=1 -s EXTRA_EXPORTED_RUNTIME_METHODS=['ccall','cwrap']")

main.cpp:

#include <iostream>
#include "emscripten.h"
#include "emscripten/val.h"
#include "thread"

extern "C" EMSCRIPTEN_KEEPALIVE void Test(){
    // directly document not working!
   auto k= emscripten::val::global("document");
    std::thread([&k](){
        EM_ASM({
                   var video= Module.emval_get_global().document.createElement("video");
                   video.setAttribute("id", "videoInput");
                   Module.emval_get_global().document.body.appendChild(video);
               });

        EM_ASM({
                   console.log(Module.emval_get_global().document.querySelector("#videoInput"));
               });

    }).detach();
    std::cout<<"Test"<<std::endl;
}

Calling Module._Test()

This error message:
worker.js onmessage() captured an uncaught exception: TypeError: Cannot read properties of undefined (reading 'createElement')

[sbc100]

The DOM is simply not accessible on the worker threads.

You would need to do all your DOM stuff on the main thread. You can run code on the main thread from a worker use the MAIN_THREAD_EM_ASM family of macros or using the proxying API (https://emscripten.org/docs/api_reference/proxying.h.html).

Alternatively you can run your setInterval on the main thread and then send work to your works via shared memory. e.g. you can store you video frame in shared memory and then notify the worker.

[moondayyy]

The DOM is simply not accessible on the worker threads.

You would need to do all your DOM stuff on the main thread. You can run code on the main thread from a worker use the MAIN_THREAD_EM_ASM family of macros or using the proxying API (https://emscripten.org/docs/api_reference/proxying.h.html).

Alternatively you can run your setInterval on the main thread and then send work to your works via shared memory. e.g. you can store you video frame in shared memory and then notify the worker.

Thank you for your answer, but I receive sound and image by listening to both the camera and the microphone.
I wanted to write multithread (worker) because it works incorrectly with a single thread.
I can listen to the microphone with a library called miniaudio, but in order to listen to the camera, I have to constantly listen in setInterval. This requires me to open a thread.