Avoid the Web Audio Worklet bootstrap processor node on browsers that support AudioWorkletScope port (#25354)

Remove the redundant Web Audio Worklet bootstrap processor node after
WebAudio/web-audio-api#2456 has been fixed.

Author: juj

src/audio_worklet.js

@@ -251,7 +251,17 @@ function createWasmAudioWorkletProcessor() {
   return WasmAudioWorkletProcessor;
 }
 
-var messagePort;
+#if MIN_FIREFOX_VERSION < 138 || MIN_CHROME_VERSION != TARGET_NOT_SUPPORTED || MIN_SAFARI_VERSION != TARGET_NOT_SUPPORTED
+// If this browser does not support the up-to-date AudioWorklet standard
+// that has a MessagePort over to the AudioWorklet, then polyfill that by
+// a hacky AudioWorkletProcessor that provides the MessagePort.
+// Firefox added support in https://hg-edge.mozilla.org/integration/autoland/rev/ab38a1796126f2b3fc06475ffc5a625059af59c1
+// Chrome ticket: https://issues.chromium.org/issues/446920095
+// Safari ticket: https://bugs.webkit.org/show_bug.cgi?id=299386
+/**
+ * @suppress {duplicate, checkTypes}
+ */
+var port = globalThis.port || {};
 
 // Specify a worklet processor that will be used to receive messages to this
 // AudioWorkletGlobalScope.  We never connect this initial AudioWorkletProcessor
@@ -260,47 +270,13 @@ class BootstrapMessages extends AudioWorkletProcessor {
   constructor(arg) {
     super();
     startWasmWorker(arg.processorOptions)
-#if WEBAUDIO_DEBUG
-    console.log('AudioWorklet global scope looks like this:');
-    console.dir(globalThis);
-#endif
     // Listen to messages from the main thread. These messages will ask this
     // scope to create the real AudioWorkletProcessors that call out to Wasm to
     // do audio processing.
-    messagePort = this.port;
-    /** @suppress {checkTypes} */
-    messagePort.onmessage = async (msg) => {
-#if MINIMAL_RUNTIME
-      // Wait for the module instantiation before processing messages.
-      await instantiatePromise;
-#endif
-      let d = msg.data;
-      if (d['_wpn']) {
-        // '_wpn' is short for 'Worklet Processor Node', using an identifier
-        // that will never conflict with user messages
-        // Register a real AudioWorkletProcessor that will actually do audio processing.
-#if AUDIO_WORKLET_SUPPORT_AUDIO_PARAMS
-        registerProcessor(d['_wpn'], createWasmAudioWorkletProcessor(d.audioParams));
-#else
-        registerProcessor(d['_wpn'], createWasmAudioWorkletProcessor());
-#endif
-#if WEBAUDIO_DEBUG
-        console.log(`Registered a new WasmAudioWorkletProcessor "${d['_wpn']}" with AudioParams: ${d.audioParams}`);
-#endif
-        // Post a Wasm Call message back telling that we have now registered the
-        // AudioWorkletProcessor, and should trigger the user onSuccess callback
-        // of the emscripten_create_wasm_audio_worklet_processor_async() call.
-        //
-        // '_wsc' is short for 'wasm call', using an identifier that will never
-        // conflict with user messages.
-        //
-        // Note: we convert the pointer arg manually here since the call site
-        // ($_EmAudioDispatchProcessorCallback) is used with various signatures
-        // and we do not know the types in advance.
-        messagePort.postMessage({'_wsc': d.callback, args: [d.contextHandle, 1/*EM_TRUE*/, {{{ to64('d.userData') }}}] });
-      } else if (d['_wsc']) {
-        getWasmTableEntry(d['_wsc'])(...d.args);
-      };
+    if (!(port instanceof MessagePort)) {
+      this.port.onmessage = port.onmessage;
+      /** @suppress {checkTypes} */
+      port = this.port;
     }
   }
 
@@ -317,5 +293,46 @@ class BootstrapMessages extends AudioWorkletProcessor {
 
 // Register the dummy processor that will just receive messages.
 registerProcessor('em-bootstrap', BootstrapMessages);
+#endif
+
+port.onmessage = async (msg) => {
+#if MINIMAL_RUNTIME
+  // Wait for the module instantiation before processing messages.
+  await instantiatePromise;
+#endif
+  let d = msg.data;
+  if (d['_boot']) {
+    startWasmWorker(d);
+#if WEBAUDIO_DEBUG
+    console.log('AudioWorklet global scope looks like this:');
+    console.dir(globalThis);
+#endif
+  } else if (d['_wpn']) {
+    // '_wpn' is short for 'Worklet Processor Node', using an identifier
+    // that will never conflict with user messages
+    // Register a real AudioWorkletProcessor that will actually do audio processing.
+#if AUDIO_WORKLET_SUPPORT_AUDIO_PARAMS
+    registerProcessor(d['_wpn'], createWasmAudioWorkletProcessor(d.audioParams));
+#else
+    registerProcessor(d['_wpn'], createWasmAudioWorkletProcessor());
+#endif
+#if WEBAUDIO_DEBUG
+    console.log(`Registered a new WasmAudioWorkletProcessor "${d['_wpn']}" with AudioParams: ${d.audioParams}`);
+#endif
+    // Post a Wasm Call message back telling that we have now registered the
+    // AudioWorkletProcessor, and should trigger the user onSuccess callback
+    // of the emscripten_create_wasm_audio_worklet_processor_async() call.
+    //
+    // '_wsc' is short for 'wasm call', using an identifier that will never
+    // conflict with user messages.
+    //
+    // Note: we convert the pointer arg manually here since the call site
+    // ($_EmAudioDispatchProcessorCallback) is used with various signatures
+    // and we do not know the types in advance.
+    port.postMessage({'_wsc': d.callback, args: [d.contextHandle, 1/*EM_TRUE*/, {{{ to64('d.userData') }}}] });
+  } else if (d['_wsc']) {
+    getWasmTableEntry(d['_wsc'])(...d.args);
+  };
+}
 
 } // ENVIRONMENT_IS_AUDIO_WORKLET

src/closure-externs/audio-worklet-externs.js

@@ -0,0 +1,11 @@
+/*
+ * AudioWorkletGlobalScope globals
+ */
+var registerProcessor = function(name, obj) {};
+var currentFrame;
+var currentTime;
+var sampleRate;
+/**
+ * @suppress {duplicate, checkTypes}
+ */
+var port;

src/closure-externs/closure-externs.js

@@ -222,14 +222,6 @@ var outerHeight;
 var event;
 var devicePixelRatio;
 
-/*
- * AudioWorkletGlobalScope globals
- */
-var registerProcessor = function(name, obj) {};
-var currentFrame;
-var currentTime;
-var sampleRate;
-
 /*
  * Avoid closure minifying anything to "id". See #13965
  */

src/lib/libwebaudio.js

@@ -192,23 +192,49 @@ var LibraryWebAudio = {
 #if WEBAUDIO_DEBUG
       console.log(`emscripten_start_wasm_audio_worklet_thread_async() addModule() completed`);
 #endif
-      audioWorklet.bootstrapMessage = new AudioWorkletNode(audioContext, 'em-bootstrap', {
-        processorOptions: {
-          // Assign the loaded AudioWorkletGlobalScope a Wasm Worker ID so that
-          // it can utilized its own TLS slots, and it is recognized to not be
-          // the main browser thread.
-          wwID: _wasmWorkersID++,
+
+#if MIN_FIREFOX_VERSION < 138 || MIN_CHROME_VERSION != TARGET_NOT_SUPPORTED || MIN_SAFARI_VERSION != TARGET_NOT_SUPPORTED
+      // If this browser does not support the up-to-date AudioWorklet standard
+      // that has a MessagePort over to the AudioWorklet, then polyfill that by
+      // instantiating a dummy AudioWorkletNode to get a MessagePort over.
+      // Firefox added support in https://hg-edge.mozilla.org/integration/autoland/rev/ab38a1796126f2b3fc06475ffc5a625059af59c1
+      // Chrome ticket: https://issues.chromium.org/issues/446920095
+      // Safari ticket: https://bugs.webkit.org/show_bug.cgi?id=299386
+      if (!audioWorklet['port']) {
+        audioWorklet['port'] = {
+          postMessage: (msg) => {
+            if (msg['_boot']) {
+              audioWorklet.bootstrapMessage = new AudioWorkletNode(audioContext, 'em-bootstrap', {
+                processorOptions: msg
+              });
+              audioWorklet.bootstrapMessage['port'].onmessage = (msg) => {
+                audioWorklet['port'].onmessage(msg);
+              }
+            } else {
+              audioWorklet.bootstrapMessage['port'].postMessage(msg);
+            }
+          }
+        }
+      }
+#endif
+
+      audioWorklet['port'].postMessage({
+        // This is the bootstrap message to the Audio Worklet.
+        '_boot': 1,
+        // Assign the loaded AudioWorkletGlobalScope a Wasm Worker ID so that
+        // it can utilized its own TLS slots, and it is recognized to not be
+        // the main browser thread.
+        wwID: _wasmWorkersID++,
 #if MINIMAL_RUNTIME
-          wasm: Module['wasm'],
+        wasm: Module['wasm'],
 #else
-          wasm: wasmModule,
+        wasm: wasmModule,
 #endif
-          wasmMemory,
-          stackLowestAddress, // sb = stack base
-          stackSize,          // sz = stack size
-        }
+        wasmMemory,
+        stackLowestAddress, // sb = stack base
+        stackSize,          // sz = stack size
       });
-      audioWorklet.bootstrapMessage.port.onmessage = _EmAudioDispatchProcessorCallback;
+      audioWorklet['port'].onmessage = _EmAudioDispatchProcessorCallback;
       {{{ makeDynCall('viip', 'callback') }}}(contextHandle, 1/*EM_TRUE*/, userData);
     }).catch(audioWorkletCreationFailed);
   },
@@ -256,7 +282,7 @@ var LibraryWebAudio = {
     console.log(`emscripten_create_wasm_audio_worklet_processor_async() creating a new AudioWorklet processor with name ${processorName}`);
 #endif
 
-    EmAudio[contextHandle].audioWorklet.bootstrapMessage.port.postMessage({
+    EmAudio[contextHandle].audioWorklet['port'].postMessage({
       // Deliberately mangled and short names used here ('_wpn', the 'Worklet
       // Processor Name' used as a 'key' to verify the message type so as to
       // not get accidentally mixed with user submitted messages, the remainder
@@ -342,11 +368,11 @@ var LibraryWebAudio = {
   emscripten_current_thread_is_audio_worklet: () => ENVIRONMENT_IS_AUDIO_WORKLET,
 
   emscripten_audio_worklet_post_function_v: (audioContext, funcPtr) => {
-    (audioContext ? EmAudio[audioContext].audioWorklet.bootstrapMessage.port : messagePort).postMessage({'_wsc': funcPtr, args: [] }); // "WaSm Call"
+    (audioContext ? EmAudio[audioContext].audioWorklet['port'] : port).postMessage({'_wsc': funcPtr, args: [] }); // "WaSm Call"
   },
 
   $emscripten_audio_worklet_post_function_1: (audioContext, funcPtr, arg0) => {
-    (audioContext ? EmAudio[audioContext].audioWorklet.bootstrapMessage.port : messagePort).postMessage({'_wsc': funcPtr, args: [arg0] }); // "WaSm Call"
+    (audioContext ? EmAudio[audioContext].audioWorklet['port'] : port).postMessage({'_wsc': funcPtr, args: [arg0] }); // "WaSm Call"
   },
 
   emscripten_audio_worklet_post_function_vi__deps: ['$emscripten_audio_worklet_post_function_1'],
@@ -360,7 +386,7 @@ var LibraryWebAudio = {
   },
 
   $emscripten_audio_worklet_post_function_2: (audioContext, funcPtr, arg0, arg1) => {
-    (audioContext ? EmAudio[audioContext].audioWorklet.bootstrapMessage.port : messagePort).postMessage({'_wsc': funcPtr, args: [arg0, arg1] }); // "WaSm Call"
+    (audioContext ? EmAudio[audioContext].audioWorklet['port'] : port).postMessage({'_wsc': funcPtr, args: [arg0, arg1] }); // "WaSm Call"
   },
 
   emscripten_audio_worklet_post_function_vii__deps: ['$emscripten_audio_worklet_post_function_2'],
@@ -374,7 +400,7 @@ var LibraryWebAudio = {
   },
 
   $emscripten_audio_worklet_post_function_3: (audioContext, funcPtr, arg0, arg1, arg2) => {
-    (audioContext ? EmAudio[audioContext].audioWorklet.bootstrapMessage.port : messagePort).postMessage({'_wsc': funcPtr, args: [arg0, arg1, arg2] }); // "WaSm Call"
+    (audioContext ? EmAudio[audioContext].audioWorklet['port'] : port).postMessage({'_wsc': funcPtr, args: [arg0, arg1, arg2] }); // "WaSm Call"
   },
   emscripten_audio_worklet_post_function_viii__deps: ['$emscripten_audio_worklet_post_function_3'],
   emscripten_audio_worklet_post_function_viii: (audioContext, funcPtr, arg0, arg1, arg2) => {
@@ -394,7 +420,7 @@ var LibraryWebAudio = {
     assert(UTF8ToString(sigPtr)[0] != 'v', 'Do NOT specify the return argument in the signature string for a call to emscripten_audio_worklet_post_function_sig(), just pass the function arguments.');
     assert(varargs);
 #endif
-    (audioContext ? EmAudio[audioContext].audioWorklet.bootstrapMessage.port : messagePort).postMessage({'_wsc': funcPtr, args: readEmAsmArgs(sigPtr, varargs) });
+    (audioContext ? EmAudio[audioContext].audioWorklet['port'] : port).postMessage({'_wsc': funcPtr, args: readEmAsmArgs(sigPtr, varargs) });
   }
 };