Minimal working example for emscripten webworker

Question

I'm trying to build a basic webworker example in C++ with emscripten. The API looks very simple, but I can't get it working. I actually wanted to implement this functionality in my project, but after failing tried to make a minimal example and it also doesn't work.

I have main.cpp:

#include <emscripten/emscripten.h>
#include <emscripten/bind.h>
#include <iostream>

namespace e = emscripten;

int counter = 0;

void cback(char* data, int size, void* arg) {
    std::cout << "Callback" << std::endl;
    counter++;
}

void loop() {
    std::cout << "Counter: " << counter << std::endl;
}

int main() {
    std::cout << "Main func." << std::endl;
    worker_handle worker = emscripten_create_worker("worker.js");
    emscripten_call_worker(worker, "one", 0, 0, cback, (void*)42);

    emscripten_set_main_loop(loop, 2, true);

    return 0;
}

and worker.cpp:

#include <iostream>
#include <emscripten/emscripten.h>

extern "C" {

void one(char* data, int size) {
    for(int i=0; i<10; i++) {
        std::cout << "Worker" << std::endl;
        emscripten_worker_respond_provisionally(0, 0);
    }
    emscripten_worker_respond(0, 0);
}
}

compiled via

emcc -std=c++11 main.cpp -o main.js
emcc -std=c++11 worker.cpp -s EXPORTED_FUNCTIONS="['_one']" -o worker.js

and a simple js load via <script> tag on the html side.

Main loads and starts, outputs Main func. and then worker js is downloaded. But neither Worker nor Callback is outputed. No errors reported.

Answer 1

Compile with BUILD_AS_WORKER flag.

emcc -std=c++11 worker.cpp -s EXPORTED_FUNCTIONS="['_one']" -s BUILD_AS_WORKER=1 -o worker.js