[AUDIO WORKLET] Support proper shutdown of audio node

src/audio_worklet.js

@@ -33,6 +33,8 @@ function createWasmAudioWorkletProcessor() {
       assert(opts.callback)
       assert(opts.samplesPerChannel)
 #endif
+      this.stopped = false;
+      this.port.onmessage = this.onmessage.bind(this);
       this.callback = {{{ makeDynCall('iipipipp', 'opts.callback') }}};
       this.userData = opts.userData;
       // Then the samples per channel to process, fixed for the lifetime of the
@@ -86,6 +88,18 @@ function createWasmAudioWorkletProcessor() {
     }
 #endif
 
+    onmessage(msg) {
+      var data = msg.data;
+      if (data['stop']) {
+        this.stopped = true;
+        if (data['cb']) {
+           // Send the same message back so that the main thread can verify that
+           // the Worklet has stopped
+          this.port.postMessage(data);
+        }
+      }
+    }
+
     /**
      * Marshals all inputs and parameters to the Wasm memory on the thread's
      * stack, then performs the wasm audio worklet call, and finally marshals
@@ -100,6 +114,8 @@ function createWasmAudioWorkletProcessor() {
     process(inputList, outputList) {
 #endif
 
+      if (this.stopped) return false;
+
 #if ALLOW_MEMORY_GROWTH
       // Recreate the output views if the heap has changed
       // TODO: add support for GROWABLE_ARRAYBUFFERS

src/lib/libsigs.js

@@ -628,6 +628,7 @@ sigs = {
   emscripten_debugger__sig: 'v',
   emscripten_destroy_audio_context__sig: 'vi',
   emscripten_destroy_web_audio_node__sig: 'vi',
+  emscripten_destroy_web_audio_node_async__sig: 'vipp',
   emscripten_destroy_worker__sig: 'vi',
   emscripten_enter_soft_fullscreen__sig: 'ipp',
   emscripten_err__sig: 'vp',

src/lib/libwebaudio.js

@@ -160,6 +160,22 @@ var LibraryWebAudio = {
 #endif
     // Explicitly disconnect the node from Web Audio graph before letting it GC,
     // to work around browser bugs such as https://webkit.org/b/222098#c23
+    EmAudio[objectHandle].port.postMessage({'stop': 1});
+    EmAudio[objectHandle].disconnect();
+    delete EmAudio[objectHandle];
+  },
+
+    emscripten_destroy_web_audio_node_async: (objectHandle, callback, userData) => {
+#if ASSERTIONS || WEBAUDIO_DEBUG
+    emAudioExpectNode(objectHandle, 'emscripten_destroy_web_audio_node_async');
+#endif
+    // Explicitly disconnect the node from Web Audio graph before letting it GC,
+    // to work around browser bugs such as https://webkit.org/b/222098#c23
+    EmAudio[objectHandle].port.postMessage({
+      'stop': 1,
+      'cb': callback,
+      'ud': userData,
+    });
     EmAudio[objectHandle].disconnect();
     delete EmAudio[objectHandle];
   },
@@ -352,7 +368,17 @@ var LibraryWebAudio = {
     dbg(`Creating AudioWorkletNode "${UTF8ToString(name)}" on context=${contextHandle} with options:`);
     console.dir(opts);
 #endif
-    return emscriptenRegisterAudioObject(new AudioWorkletNode(EmAudio[contextHandle], UTF8ToString(name), opts));
+
+    const node = new AudioWorkletNode(EmAudio[contextHandle], UTF8ToString(name), opts);
+    node.port.onmessage = (msg) => {
+      var data = msg.data;
+      if (data['stop']) {
+        var cb = data['cb'];
+        callUserCallback(() => {{{ makeDynCall('vp', 'cb') }}}(data['ud']));
+      }
+    };
+
+    return emscriptenRegisterAudioObject(node);
   },
 #endif // ~AUDIO_WORKLET
 

system/include/emscripten/webaudio.h

@@ -60,11 +60,24 @@ typedef void (*EmscriptenStartWebAudioWorkletCallback)(EMSCRIPTEN_WEBAUDIO_T aud
 // after calling this function.
 void emscripten_destroy_audio_context(EMSCRIPTEN_WEBAUDIO_T audioContext);
 
-// Disconnects the given audio node from its audio graph, and then releases
+// Disconnects the given audio node from its audio graph, make sure the
+// process callback is not called anymore and then releases
 // the JS object table reference to the given audio node. The specified handle
 // is invalid after calling this function.
+// The process callback can be called after this function is called.
+// If you need to ensure that the process callback is not called anymore, use
+// emscripten_destroy_web_audio_node_async() instead.
 void emscripten_destroy_web_audio_node(EMSCRIPTEN_WEBAUDIO_T objectHandle);
 
+typedef void (*EmscriptenDestroyWebAudioNodeCallback)(void *userData3);
+
+// Disconnects the given audio node from its audio graph, make sure the
+// process callback is not called anymore and then releases
+// the JS object table reference to the given audio node. The specified handle
+// is invalid after calling this function.
+// Once the node has been verified to be stopped, the callback will be called.
+void emscripten_destroy_web_audio_node_async(EMSCRIPTEN_WEBAUDIO_T objectHandle, EmscriptenDestroyWebAudioNodeCallback callback, void *userData3);
+
 // Create Wasm AudioWorklet thread. Call this function once at application startup to establish an AudioWorkletGlobalScope for your app.
 // After the scope has been initialized, the given callback will fire.
 // audioContext: The Web Audio context object to initialize the Wasm AudioWorklet thread on. Each AudioContext can have only one AudioWorklet

test/test_interactive.py

@@ -298,6 +298,9 @@ def test_audio_worklet(self):
     self.btest('webaudio/audioworklet.c', expected='0', cflags=['-sAUDIO_WORKLET', '-sWASM_WORKERS', '--preload-file', test_file('hello_world.c') + '@/'])
     self.btest('webaudio/audioworklet.c', expected='0', cflags=['-sAUDIO_WORKLET', '-sWASM_WORKERS', '-pthread'])
 
+  def test_audio_worklet_destroy_async(self):
+    self.btest('webaudio/audioworklet_destroy_async.c', expected='0', cflags=['-sAUDIO_WORKLET', '-sWASM_WORKERS', '-pthread', '-lwebaudio.js'])
+
   # Tests a second AudioWorklet example: sine wave tone generator.
   def test_audio_worklet_tone_generator(self):
     self.btest('webaudio/audio_worklet_tone_generator.c', expected='0', cflags=['-sAUDIO_WORKLET', '-sWASM_WORKERS'])

test/webaudio/audioworklet_destroy_async.c

@@ -0,0 +1,107 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <emscripten.h>
+#include <emscripten/webaudio.h>
+#include <emscripten/threading.h>
+#include <stdatomic.h>
+
+#ifdef REPORT_RESULT
+volatile int audioProcessedCount = 0;
+int valueAfterDestroy;
+#endif
+
+EMSCRIPTEN_AUDIO_WORKLET_NODE_T node_id;
+
+bool ProcessAudio(int numInputs, const AudioSampleFrame *inputs, int numOutputs, AudioSampleFrame *outputs, int numParams, const AudioParamFrame *params, void *userData) {
+#ifdef REPORT_RESULT
+  ++audioProcessedCount;
+#endif
+
+  // Produce noise in all output channels.
+  for(int i = 0; i < numOutputs; ++i)
+    for(int j = 0; j < outputs[i].samplesPerChannel*outputs[i].numberOfChannels; ++j)
+      outputs[i].data[j] = (rand() / (float)RAND_MAX * 2.0f - 1.0f) * 0.3f;
+
+  return true;
+}
+
+void observe_after_destroy(void * userData) {
+  printf("Expected processed count to be %d, was %d\n", valueAfterDestroy, audioProcessedCount);
+
+#ifdef REPORT_RESULT
+  if (audioProcessedCount == valueAfterDestroy) {
+      printf("Test PASSED!\n");
+      REPORT_RESULT(0);
+  } else {
+    printf("Test FAILED!\n");
+    REPORT_RESULT(1);
+  }
+#endif
+}
+
+void AudioWorkletDestroyed(void* userData) {
+  emscripten_out("AudioWorkletDestroyed");
+#ifdef REPORT_RESULT
+  valueAfterDestroy = audioProcessedCount;
+#endif
+  emscripten_set_timeout(observe_after_destroy, 1000, 0);
+}
+
+void observe_after_start(void *userData) {
+#ifdef REPORT_RESULT
+  if (audioProcessedCount == 0) {
+    printf("Test FAILED!\n");
+    REPORT_RESULT(1);
+  }
+#endif
+
+  emscripten_destroy_web_audio_node_async(node_id, &AudioWorkletDestroyed, 0);
+}
+
+// This callback will fire after the Audio Worklet Processor has finished being
+// added to the Worklet global scope.
+void AudioWorkletProcessorCreated(EMSCRIPTEN_WEBAUDIO_T audioContext, bool success, void *userData) {
+  if (!success) return;
+
+  emscripten_out("AudioWorkletProcessorCreated");
+
+  // Specify the input and output node configurations for the Wasm Audio
+  // Worklet. A simple setup with single mono output channel here, and no
+  // inputs.
+  int outputChannelCounts[1] = { 1 };
+
+  EmscriptenAudioWorkletNodeCreateOptions options = {
+    .numberOfInputs = 0,
+    .numberOfOutputs = 1,
+    .outputChannelCounts = outputChannelCounts
+  };
+
+  // Instantiate the counter-incrementer Audio Worklet Processor.
+  node_id = emscripten_create_wasm_audio_worklet_node(audioContext, "counter-incrementer", &options, &ProcessAudio, 0);
+  emscripten_audio_node_connect(node_id, audioContext, 0, 0);
+
+  // Wait 1s to check that the counter has started incrementing
+  emscripten_set_timeout(observe_after_start, 1000, 0);
+}
+
+// This callback will fire when the audio worklet thread has been initialized.
+void WebAudioWorkletThreadInitialized(EMSCRIPTEN_WEBAUDIO_T audioContext, bool success, void *userData) {
+  if (!success) return;
+
+  emscripten_out("WebAudioWorkletThreadInitialized");
+
+  WebAudioWorkletProcessorCreateOptions opts = {
+    .name = "counter-incrementer",
+  };
+  emscripten_create_wasm_audio_worklet_processor_async(audioContext, &opts, AudioWorkletProcessorCreated, 0);
+}
+
+uint8_t wasmAudioWorkletStack[4096];
+
+int main() {
+  EMSCRIPTEN_WEBAUDIO_T context = emscripten_create_audio_context(NULL);
+
+  emscripten_start_wasm_audio_worklet_thread_async(context, wasmAudioWorkletStack, sizeof(wasmAudioWorkletStack), WebAudioWorkletThreadInitialized, 0);
+
+  return 0;
+}