Basic support for running Emscripten code as AudioWorklets

ChangeLog.md

@@ -161,6 +161,9 @@ See docs/process.md for more on how version tagging works.
   existence of `Buffer.from` which was added in v5.10.0.  If it turns out
   there is still a need to support these older node versions we can
   add a polyfil under LEGACY_VM_SUPPORT (#14447).
+- Added support for running Emscripten-compiled native code in AudioWorklets as
+  if they were regular pthreads. See `/tests/audioworklet/tone/` for a working 
+  minimal example.
 
 2.0.24 - 06/10/2021
 -------------------
@@ -192,6 +195,9 @@ See docs/process.md for more on how version tagging works.
 - You can now explicitly request that an environment variable remain unset by
   setting its value in `ENV` to `undefined`. This is useful for variables, such
   as `LANG`, for which Emscripten normally provides a default value.
+- Added support for running Emscripten-compiled native code in AudioWorklets as
+  if they were regular pthreads. See `/tests/audioworklet/tone/` for a working 
+  minimal example.
 
 2.0.23 - 05/26/2021
 -------------------

emcc.py

@@ -146,7 +146,7 @@
 }
 
 
-VALID_ENVIRONMENTS = ('web', 'webview', 'worker', 'node', 'shell')
+VALID_ENVIRONMENTS = ('web', 'webview', 'worker', 'node', 'shell', 'audioworklet')
 SIMD_INTEL_FEATURE_TOWER = ['-msse', '-msse2', '-msse3', '-mssse3', '-msse4.1', '-msse4.2', '-mavx']
 SIMD_NEON_FLAGS = ['-mfpu=neon']
 COMPILE_ONLY_FLAGS = set(['--default-obj-ext'])
@@ -297,6 +297,9 @@ def setup_environment_settings():
       'worker' in environments or \
       (settings.ENVIRONMENT_MAY_BE_NODE and settings.USE_PTHREADS)
 
+  # Worklet environment must be enabled explicitly for now
+  settings.ENVIRONMENT_MAY_BE_AUDIOWORKLET = 'audioworklet' in environments
+
   if not settings.ENVIRONMENT_MAY_BE_WORKER and settings.PROXY_TO_WORKER:
     exit_with_error('If you specify --proxy-to-worker and specify a "-s ENVIRONMENT=" directive, it must include "worker" as a target! (Try e.g. -s ENVIRONMENT=web,worker)')
 
@@ -1953,6 +1956,10 @@ def default_setting(name, new_default):
       '_pthread_testcancel',
       '_exit',
     ]
+    if settings.ENVIRONMENT_MAY_BE_AUDIOWORKLET:
+      settings.EXPORTED_FUNCTIONS += [
+        '_pthread_create',
+      ]
     settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE += [
       '$exitOnMainThread',
     ]
@@ -3380,7 +3387,6 @@ def modularize():
     f.write(src)
 
     # Export using a UMD style export, or ES6 exports if selected
-
     if settings.EXPORT_ES6:
       f.write('export default %s;' % settings.EXPORT_NAME)
     elif not settings.MINIMAL_RUNTIME:
@@ -3393,6 +3399,12 @@ def modularize():
   exports["%(EXPORT_NAME)s"] = %(EXPORT_NAME)s;
 ''' % {'EXPORT_NAME': settings.EXPORT_NAME})
 
+    # Store the export on the global scope for audio worklets
+    if settings.ENVIRONMENT_MAY_BE_AUDIOWORKLET:
+      f.write(f'''if (typeof AudioWorkletGlobalScope === 'function')
+  globalThis["{settings.EXPORT_NAME}"] = {settings.EXPORT_NAME};
+''')
+
   shared.configuration.get_temp_files().note(final_js)
   save_intermediate('modularized')
 

src/library.js

@@ -3434,7 +3434,7 @@ LibraryManager.library = {
   $setWasmTableEntry__deps: ['$wasmTableMirror'],
   $setWasmTableEntry: function(idx, func) {
     wasmTable.set(idx, func);
-    wasmTableMirror[idx] = func;
+    wasmTableMirror[idx] = wasmTable.get(idx);
   },
 
   $getWasmTableEntry__internal: true,