Avoid calling addEventListener in audio worklet

[m4burns]

When building an application that uses both an audio worklet and a normal worker, the main module wrapper (a.out.js) calls addEventListener whenever ENVIRONMENT_IS_WASM_WORKER. This flag is set for audio worklets, but addEventListener is not available in the audio worker global scope. The audio worklet load process then fails.

This doesn't occur when using only the audio worklet APIs, because _emscripten_create_wasm_worker__postset doesn't happen. There's already a check to prevent a similar error just above the lines modified by this PR: https://github.com/emscripten-core/emscripten/blob/fa80cf25b8641974d60605b8a24cb7150fd63701/src/library_wasm_worker.js#L112C5-L112C58 so the missing check here seems like an oversight.

Here's a minimal example that reproduces the failure:

#include <emscripten/webaudio.h>
#include <emscripten/wasm_worker.h>
#include <stdio.h>

void run_in_worker()
{
  printf("Hello from Worker!\n");
}

uint8_t audioThreadStack[4096];

EM_BOOL Callback(int numInputs, const AudioSampleFrame *inputs,
                 int numOutputs, AudioSampleFrame *outputs,
                 int numParams, const AudioParamFrame *params,
                 void *userData)
{
  return EM_TRUE;
}

void AudioWorkletProcessorCreated(EMSCRIPTEN_WEBAUDIO_T audioContext, EM_BOOL success, void *userData)
{
  if (!success) return;

  int outputChannelCounts[1] = { 1 };
  EmscriptenAudioWorkletNodeCreateOptions options = {
    .numberOfInputs = 0,
    .numberOfOutputs = 1,
    .outputChannelCounts = outputChannelCounts
  };

  EMSCRIPTEN_AUDIO_WORKLET_NODE_T wasmAudioWorklet = emscripten_create_wasm_audio_worklet_node(audioContext, "my-node", &options, &Callback, 0);

  EM_ASM({emscriptenGetAudioObject($0).connect(emscriptenGetAudioObject($1).destination)},
    wasmAudioWorklet, audioContext);
}

void AudioThreadInitialized(EMSCRIPTEN_WEBAUDIO_T audioContext, EM_BOOL success, void *userData)
{
  if (!success) return;

  WebAudioWorkletProcessorCreateOptions opts = {
    .name = "my-node",
  };
  emscripten_create_wasm_audio_worklet_processor_async(audioContext, &opts, &AudioWorkletProcessorCreated, 0);
}

int main()
{
  emscripten_wasm_worker_t worker = emscripten_malloc_wasm_worker(/*stackSize: */1024);
  emscripten_wasm_worker_post_function_v(worker, run_in_worker);
  
  EMSCRIPTEN_WEBAUDIO_T context = emscripten_create_audio_context(0);

  emscripten_start_wasm_audio_worklet_thread_async(context, audioThreadStack, sizeof(audioThreadStack), &AudioThreadInitialized, 0);
}

Build with emcc -sAUDIO_WORKLET=1 -sWASM_WORKERS=1 example.cc

[sbc100]

I might be good to add a test for this to test_browser.py (a test that uses audio worklets and wasm workers together).

[m4burns]

I just added a test that uses audio worklets and workers at the same time. Thanks for the quick reviews!

[sbc100]

lgtm

@juj could you take a look too?

[juj]

Great work on the test. LGTM with a small update.