Nsryjdtyk

I'm trying to use Emscripten to write a Software to run in browser but also on other architectures (e.g. Android, PC-standalone app).

The Software structure is something like this:

main_program_loop() {

   if (gui.button_clicked()) {

      run_async(some_complex_action, gui.text_field.to_string())

   }

   if (some_complex_action_has_finished())

   {

      make_use_of(get_result_from_complex_action());

   }

}



some_complex_action(string_argument)

{

    some_object = read_local(string_argument);

    interm_res = simple_computation(some_object);

    other_object = expensive_computation(interm_res);

    send_remote(some_object.member_var, other_object);

    return other_object.member_var;

}

Let's call main_program_loop the GUI or frontend, some_complex_action the intermediate layer, and read_local, send_remode and expensive_computation the backend or lower layer.

Now the frontend and backend would be architecture specific (e.g. for Javascript read_local could use IndexDB, send_remote could use fetch),
but the intermediate layer should make up more then 50% of the code (that's why I do not want to write it two times in two different languages, and instead write it once in C and transpile it to Javascript, for Android I would use JNI).

Problems come in since in Javascript the functions on the lowest layer (fetch etc) run asyncronously (return a promise or require a callback).

One approach I tried was to use promises and send IDs through the intermediate layer

var promises = {};

var last_id = 0;

handle_click() {

    var id = Module.ccall('some_complex_action', 'number', ['string'], [text_field.value]);

    promises[id].then((result) => make_us_of(result));

}



recv_remote: function(str) {

    promises[last_id] = fetch(get_url(str)).then((response) => response.arrayBuffer());

    last_id += 1;

    return last_id - 1;

}

It works for the simple case of

some_complex_action(char *str)

{

    return recv_remote(str);

}

But for real cases it seem to be getting really complicated, maybe impossible. (I tried some approach where I'd given every function a state and every time a backend function finishes, the function is recalled and advances it's state or so, but the code started getting complicated like hell.) To compare, if I was to call some_complex_action from C or Java, I'd just call it in a thread separate from the GUI thread, and inside the thread everything would happen synchronously.

I wished I could just call some_complex_action from an async function and put await inside recv_remote but of cause I can put await only directly in the async function, not in some function called down the line. So that idea did not work out either.

Ideally if somehow I could stop execution of the intermediate Emscripten transpiled code until the backend function has completed, then return from the backend function with the result and continue executing the transpiled code.

Has anyone used Emterpreter and can imagine that it could help me get to my goal?

Any ideas what I could do?