如何在Web Worker中使用emscripted .js库

Question

I've compiled my program into a single program.js file, and within the worker, I call:

importScripts('program.js');
Module.callMain();

However, although callMain is executing, within that function invocation's stack I am getting the Undefined is not a function error.

My hunch is that I haven't read some essential emscripten documentation, wiki, or sourcecode.

What I know:

• emscripten has bindings to work with workers, but only when there is an emscripted process on the main thread to use these bindings (see emscripten.h )
• In order to compile a task (within a library that runs on the main thread) to a worker, emcc needs special options passed at compile time for that task (see settings.js )

What I surmise:

• There may be flags that I need to pass to let emcc know not to call functions on nonexistent objects, like window
• Having looked through the implementation of /dev/tty , which is linked to by /dev/stdin , and the implementation of /dev/stdout , I believe there may be output to the console , which I don't believe is supported in a worker

What I am asking:

• How can I use my library, a single js file, in a worker?
  • My library loads other files from a program.data file, if that makes a difference

Thanks in advance. Please let me know if I can add any details.

---

Note: the code at top is simplified - it doesn't seem to be an error in syntax.

Update:

• The stacktrace ( Error.stack ) only tells me that the error occured in Module.callMain . It does not tell me anything about the imported script that might be causing it. :(

Answer 1

Emscripten output should run on a website, on a web worker, or in node, all without modifications. There might be some limitations (eg no canvas to render to in a worker), but otherwise it is just pure JS that can run in those three environments.

Does the exact same JS file that emscripten generated work outside of a worker?

If callMain() fails, check that your project has a main() function.

Answer 2

Immediately after loading the js (by importScripts() ) it may not be executed yet, hence you are not ready. You can ask Emscripten to call a callback for you when things are ready. You will have functions accessible via the variable Module .

var Module = {
    preRun:[],
    onRuntimeInitialized: function load_done_callback() {
        console.info("The Module is loaded and is accessible here", Module);
        console.inf("no need to call main() though", Module._main); // add "_" before your function names
    },
};

importScripts('program.js');

No need to call callMain() or Module._main() , it will be called for you. You may need to set NO_EXIT_RUNTIME=1 in compiler command line:

em++  \
  -s EXPORTED_FUNCTIONS="['_main', '_myfunction1' , '_my_function2' ]" \
  -s NO_EXIT_RUNTIME=1 \
  -s DEMANGLE_SUPPORT=1 \
  program.cpp \
  -o ./program.js

Note that you don't need to compile as worker in this case where you use importScripts() .