Extend hybrid pthread/wasm-workers support for Audio Worklets. NFC

Prior to this change calling pthread functions from an audio worklet
context was undefined behaviour.

Followup to #26777

Author: sbc100

src/lib/libsigs.js

@@ -314,7 +314,8 @@ sigs = {
   _embind_register_value_object__sig: 'vpppppp',
   _embind_register_value_object_field__sig: 'vpppppppppp',
   _embind_register_void__sig: 'vpp',
-  _emscripten_create_audio_worklet__sig: 'viipipp',
+  _emscripten_create_audio_worklet__sig: 'viipipipp',
+
   _emscripten_create_wasm_worker__sig: 'iipip',
   _emscripten_dlopen_js__sig: 'vpppp',
   _emscripten_dlsync_threads__sig: 'v',

src/lib/libwebaudio.js

@@ -170,7 +170,7 @@ var LibraryWebAudio = {
   _emscripten_create_audio_worklet__deps: [
     '$_emAudioDispatchProcessorCallback',
     '$stackAlloc', '$stackRestore', '$stackSave'],
-  _emscripten_create_audio_worklet: (wwID, contextHandle, stackLowestAddress, stackSize, callback, userData) => {
+  _emscripten_create_audio_worklet: (wwID, contextHandle, stackLowestAddress, stackSize, pthreadPtr, callback, userData) => {
 
 #if ASSERTIONS || WEBAUDIO_DEBUG
     emAudioExpectContext(contextHandle, '_emscripten_create_audio_worklet');
@@ -256,6 +256,9 @@ var LibraryWebAudio = {
         wasmMemory,
         stackLowestAddress, // sb = stack base
         stackSize,          // sz = stack size
+#if PTHREADS
+        pthreadPtr,
+#endif
       });
       audioWorklet.port.onmessage = _emAudioDispatchProcessorCallback;
       {{{ makeDynCall('viip', 'callback') }}}(contextHandle, 1/*EM_TRUE*/, userData);

system/lib/libc/emscripten_internal.h

@@ -137,7 +137,7 @@ void emscripten_fetch_free(unsigned int);
 // to perform the wasm worker creation.
 bool _emscripten_create_wasm_worker(emscripten_wasm_worker_t wwID, void *stackLowestAddress, uint32_t stackSize, void* pthreadPtr);
 
-void _emscripten_create_audio_worklet(emscripten_wasm_worker_t wwID, EMSCRIPTEN_WEBAUDIO_T audioContext, void *stackLowestAddress, uint32_t stackSize, EmscriptenStartWebAudioWorkletCallback callback, void *userData2);
+void _emscripten_create_audio_worklet(emscripten_wasm_worker_t wwID, EMSCRIPTEN_WEBAUDIO_T audioContext, void *stackLowestAddress, uint32_t stackSize, void* pthreadPtr, EmscriptenStartWebAudioWorkletCallback callback, void *userData2);
 
 void __resumeException(void* exn);
 void __cxa_call_unexpected(void* exn);

system/lib/pthread/threading_internal.h

@@ -120,6 +120,12 @@ int _emscripten_thread_supports_atomics_wait(void);
 
 pid_t _emscripten_get_next_tid();
 
+// Initialize pthread data, at start of memory region pointed to `base`.
+// `size` is an in/out parameter representing the size of the `base` region
+// on input, and the size of new/adjusted region on output.
+// Return a new/adjusted memory base to be used to stack/tls data.
+void* _emscripten_init_pthread(void *base, size_t* size, pid_t tid);
+
 // Wake the target thread in case it is blocked in emscripten_futex_wait.
 // Note: If threads directly use lower level APIs such
 // __builtin_wasm_memory_atomic_waitXX then they will not be woken by

system/lib/wasm_worker/audio_worklet.c

@@ -13,5 +13,12 @@
 // Simple wrapper function around the JS _emscripten_create_audio_worklet
 // function that adds the _emscripten_get_next_tid() as arg0
 void emscripten_start_wasm_audio_worklet_thread_async(EMSCRIPTEN_WEBAUDIO_T audioContext, void *stackLowestAddress, uint32_t stackSize, EmscriptenStartWebAudioWorkletCallback callback, void *userData2) {
-  _emscripten_create_audio_worklet(_emscripten_get_next_tid(), audioContext, stackLowestAddress, stackSize, callback, userData2);
+  emscripten_wasm_worker_t wwID = _emscripten_get_next_tid();
+  void* pthreadPtr = stackLowestAddress;
+#ifdef __EMSCRIPTEN_PTHREADS__
+  size_t stackSize_ = stackSize;
+  stackLowestAddress = _emscripten_init_pthread(stackLowestAddress, &stackSize_, wwID);
+  stackSize = stackSize_;
+#endif
+  _emscripten_create_audio_worklet(wwID, audioContext, stackLowestAddress, stackSize, pthreadPtr, callback, userData2);
 }

system/lib/wasm_worker/library_wasm_worker.c

@@ -94,7 +94,7 @@ weak_alias(dummy, __pthread_tsd_size);
  * In either case these sections are all aligned to `max_alignment()`
  * which is the max alignment of any of the given chunks.
  */
-static void* init_pthread_struct(void *stackPlusTLSAddress, pid_t tid, size_t* stackPlusTLSSize) {
+void* _emscripten_init_pthread(void *stackPlusTLSAddress, size_t* stackPlusTLSSize, pid_t tid) {
   // TODO: Remove duplication with pthread_create
   pthread_t self = pthread_self();
 
@@ -143,7 +143,7 @@ static void* init_pthread_struct(void *stackPlusTLSAddress, pid_t tid, size_t* s
 
   __tl_unlock();
 
-  dbg("init_pthread_struct: base=%#lx, end=%#lx, used=%zu "
+  dbg("_emscripten_init_pthread: base=%#lx, end=%#lx, used=%zu "
       "stackold=%zu stacknew=%zu",
       base,
       base + *stackPlusTLSSize,
@@ -202,7 +202,7 @@ emscripten_wasm_worker_t emscripten_create_wasm_worker(void *stackPlusTLSAddress
   emscripten_wasm_worker_t wwID = _emscripten_get_next_tid();
   void* pthreadPtr = stackPlusTLSAddress;
 #ifdef __EMSCRIPTEN_PTHREADS__
-  stackPlusTLSAddress = init_pthread_struct(stackPlusTLSAddress, wwID, &stackPlusTLSSize);
+  stackPlusTLSAddress = _emscripten_init_pthread(stackPlusTLSAddress, &stackPlusTLSSize, wwID);
 #endif
   if (!_emscripten_create_wasm_worker(wwID, stackPlusTLSAddress, stackPlusTLSSize, pthreadPtr))
     return 0;