From b298f2deffeae71eb96750629df3c6d10148c311 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Thu, 4 Dec 2025 17:09:03 +0100
Subject: [PATCH 01/17] Complete rethink of the test

---
 test/webaudio/audioworklet_emscripten_locks.c | 284 ++++++++++--------
 1 file changed, 154 insertions(+), 130 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 20471eced5f63..90b2684d73058 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -1,4 +1,3 @@
-#include <emscripten/threading.h>
 #include <emscripten/wasm_worker.h>
 #include <emscripten/webaudio.h>
 #include <assert.h>
@@ -7,180 +6,205 @@
 //
 // - _emscripten_thread_supports_atomics_wait()
 // - emscripten_lock_init()
-// - emscripten_lock_try_acquire()
 // - emscripten_lock_busyspin_wait_acquire()
-// - emscripten_lock_busyspin_waitinf_acquire()
 // - emscripten_lock_release()
-// - emscripten_get_now()
+// - emscripten_get_now() in AW
+
+// Build with emcc -sAUDIO_WORKLET -sWASM_WORKERS -pthread -O1 -g -o index.html audioworklet_emscripten_locks.c
+
+// Values -1.5373, 77.2259, -251.4728
+// Values -0.9080, -42.4902, -250.6685
+
+// Marks a function to be kept in the Module and exposed to script (instead of adding to EXPORTED_FUNCTIONS)
+#ifndef KEEP_IN_MODULE
+#define KEEP_IN_MODULE __attribute__((used, visibility("default")))
+#endif
+
+// This needs to be big enough for a stereo output (1024 with a 128 frame) + working stack
+#define AUDIO_STACK_SIZE 2048
 
 // Internal, found in 'system/lib/pthread/threading_internal.h' (and requires building with -pthread)
 int _emscripten_thread_supports_atomics_wait(void);
 
 typedef enum {
-  // No wait support in audio worklets
-  TEST_HAS_WAIT,
-  // Acquired in main, fail in process
-  TEST_TRY_ACQUIRE,
-  // Keep acquired so time-out
-  TEST_WAIT_ACQUIRE_FAIL,
-  // Release in main, succeed in process
-  TEST_WAIT_ACQUIRE,
-  // Release in process after above
-  TEST_RELEASE,
-  // Released in process above, spin in main
-  TEST_WAIT_INFINTE_1,
-  // Release in process to stop spinning in main
-  TEST_WAIT_INFINTE_2,
-  // Call emscripten_get_now() in process
-  TEST_GET_NOW,
+  // The test hasn't yet started
+  TEST_NOT_STARTED,
+  // Worklet ready and running the test
+  TEST_RUNNING,
+  // Main thread is finished, wait on worklet
+  TEST_DONE_MAIN,
   // Test finished
   TEST_DONE
 } Test;
 
+// Global audio context
+EMSCRIPTEN_WEBAUDIO_T context;
 // Lock used in all the tests
 emscripten_lock_t testLock = EMSCRIPTEN_LOCK_T_STATIC_INITIALIZER;
 // Which test is running (sometimes in the worklet, sometimes in the main thread)
-_Atomic Test whichTest = TEST_HAS_WAIT;
+_Atomic Test whichTest = TEST_NOT_STARTED;
 // Time at which the test starts taken in main()
 double startTime = 0;
 
-bool ProcessAudio(int numInputs, const AudioSampleFrame *inputs, int numOutputs, AudioSampleFrame *outputs, int numParams, const AudioParamFrame *params, void *userData) {
-  assert(emscripten_current_thread_is_audio_worklet());
+// Counter for main, accessed only by main
+int howManyMain = 0;
+// Counter for the audio worklet, accessed only by the AW
+int howManyProc = 0;
+
+// Our dummy container
+typedef struct Dummy {
+  uint32_t val0;
+  uint32_t val1;
+  uint32_t val2;
+} Dummy;
+
+// Start values
+void initDummy(Dummy* dummy) {
+  dummy->val0 = 4;
+  dummy->val1 = 1;
+  dummy->val2 = 2;
+}
 
-  // Produce at few empty frames of audio before we start trying to interact
-  // with the with main thread.
-  // On chrome at least it appears the main thread completely blocks until
-  // a few frames have been produced.  This means it may not be safe to interact
-  // with the main thread during initial frames?
-  // In my experiments it seems like 5 was the magic number that I needed to
-  // produce before the main thread could continue to run.
-  // See https://github.com/emscripten-core/emscripten/issues/24213
-  static int count = 0;
-  if (count++ < 5) return true;
-
-  int result = 0;
-  switch (whichTest) {
-  case TEST_HAS_WAIT:
-    // Should not have wait support here
-    result = _emscripten_thread_supports_atomics_wait();
-    emscripten_outf("TEST_HAS_WAIT: %d (expect: 0)", result);
-    assert(!result);
-    whichTest = TEST_TRY_ACQUIRE;
-    break;
-  case TEST_TRY_ACQUIRE:
-    // Was locked after init, should fail to acquire
-    result = emscripten_lock_try_acquire(&testLock);
-    emscripten_outf("TEST_TRY_ACQUIRE: %d (expect: 0)", result);
-    assert(!result);
-    whichTest = TEST_WAIT_ACQUIRE_FAIL;
-    break;
-  case TEST_WAIT_ACQUIRE_FAIL:
-    // Still locked so we fail to acquire
-    result = emscripten_lock_busyspin_wait_acquire(&testLock, 100);
-    emscripten_outf("TEST_WAIT_ACQUIRE_FAIL: %d (expect: 0)", result);
-    assert(!result);
-    whichTest = TEST_WAIT_ACQUIRE;
-  case TEST_WAIT_ACQUIRE:
-    // Will get unlocked in main thread, so should quickly acquire
-    result = emscripten_lock_busyspin_wait_acquire(&testLock, 10000);
-    emscripten_outf("TEST_WAIT_ACQUIRE: %d  (expect: 1)", result);
-    assert(result);
-    whichTest = TEST_RELEASE;
-    break;
-  case TEST_RELEASE:
-    // Unlock, check the result
+void printDummy(Dummy* dummy) {
+  emscripten_outf("Values: %u, %u, %u", dummy->val0, dummy->val1, dummy->val2);
+}
+
+// Run a simple calculation that will only be stable *if* all values are atomically updated
+void runCalcs(Dummy* dummy, int num) {
+  for (int n = 0; n < num; n++) {
+    int have = emscripten_lock_busyspin_wait_acquire(&testLock, 100);
+    assert(have);
+    dummy->val0 += dummy->val1 * dummy->val2;
+    dummy->val1 += dummy->val2 * dummy->val0;
+    dummy->val2 += dummy->val0 * dummy->val1;
+    dummy->val0 /= 4;
+    dummy->val1 /= 3;
+    dummy->val2 /= 2;
     emscripten_lock_release(&testLock);
-    result = emscripten_lock_try_acquire(&testLock);
-    emscripten_outf("TEST_RELEASE: %d (expect: 1)", result);
-    assert(result);
-    whichTest = TEST_WAIT_INFINTE_1;
-    break;
-  case TEST_WAIT_INFINTE_1:
-    // Still locked when we enter here but move on in the main thread
+  }
+}
+
+void stopping() {
+  emscripten_out("Expect: 949807601, 1303780836, 243502614");
+  emscripten_out("Ending test");
+  emscripten_destroy_audio_context(context);
+  emscripten_force_exit(0);
+}
+
+// AW callback
+bool process(int numInputs, const AudioSampleFrame* inputs, int numOutputs, AudioSampleFrame* outputs, int numParams, const AudioParamFrame* params, void* data) {
+  assert(emscripten_current_thread_is_audio_worklet());
+  switch (whichTest) {
+  case TEST_NOT_STARTED:
+    whichTest = TEST_RUNNING;
     break;
-  case TEST_WAIT_INFINTE_2:
-    emscripten_lock_release(&testLock);
-    whichTest = TEST_GET_NOW;
+  case TEST_RUNNING:
+  case TEST_DONE_MAIN:
+    if (howManyProc-- > 0) {
+      runCalcs((Dummy*) data, 250);
+    } else {
+      if (whichTest == TEST_DONE_MAIN) {
+        // Both loops are finished
+        whichTest = TEST_DONE;
+      }
+    }
     break;
-  case TEST_GET_NOW:
-    result = (int) (emscripten_get_now() - startTime);
-    emscripten_outf("TEST_GET_NOW: %d  (expect: > 0)", result);
-    assert(result > 0);
-    whichTest = TEST_DONE;
   case TEST_DONE:
+    emscripten_outf("Took %dms (expect: > 0)", (int) (emscripten_get_now() - startTime));
     return false;
-  default:
-    break;
   }
   return true;
 }
 
-EM_JS(void, InitHtmlUi, (EMSCRIPTEN_WEBAUDIO_T audioContext), {
-  let startButton = document.createElement('button');
-  startButton.innerHTML = 'Start playback';
-  document.body.appendChild(startButton);
-
-  audioContext = emscriptenGetAudioObject(audioContext);
-  startButton.onclick = () => {
-    audioContext.resume();
-  };
-});
-
-bool MainLoop(double time, void* data) {
+// Main thread callback
+bool mainLoop(double time, void* data) {
   assert(!emscripten_current_thread_is_audio_worklet());
-  static int didUnlock = false;
   switch (whichTest) {
-  case TEST_WAIT_ACQUIRE:
-    if (!didUnlock) {
-      emscripten_out("main thread releasing lock");
-      // Release here to acquire in process
-      emscripten_lock_release(&testLock);
-      didUnlock = true;
+  case TEST_NOT_STARTED:
+    break;
+  case TEST_RUNNING:
+    if (howManyMain-- > 0) {
+      runCalcs((Dummy*) data, 1000);
+    } else {
+      // Done here, so signal to process()
+      whichTest = TEST_DONE_MAIN;
     }
     break;
-  case TEST_WAIT_INFINTE_1:
-    // Spin here until released in process (but don't change test until we know this case ran)
-    whichTest = TEST_WAIT_INFINTE_2;
-    emscripten_lock_busyspin_waitinf_acquire(&testLock);
-    emscripten_out("TEST_WAIT_INFINTE (from main)");
+  case TEST_DONE_MAIN:
+    // Wait for process() to finish
     break;
   case TEST_DONE:
-    // Finished, exit from the main thread
-    emscripten_out("Test success");
-    emscripten_force_exit(0);
+    printDummy((Dummy*) data);
+    // 32-bit maths with locks *should* result in these:
+    assert(((Dummy*) data)->val0 ==  949807601
+        && ((Dummy*) data)->val1 == 1303780836
+        && ((Dummy*) data)->val2 ==  243502614);
+    stopping();
     return false;
-  default:
-    break;
   }
   return true;
 }
 
-void AudioWorkletProcessorCreated(EMSCRIPTEN_WEBAUDIO_T audioContext, bool success, void *userData) {
-  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, "noise-generator", &options, &ProcessAudio, NULL);
-  emscripten_audio_node_connect(wasmAudioWorklet, audioContext, 0, 0);
-  InitHtmlUi(audioContext);
+KEEP_IN_MODULE void startTest() {
+  startTime = emscripten_get_now();
+  if (emscripten_audio_context_state(context) != AUDIO_CONTEXT_STATE_RUNNING) {
+    emscripten_resume_audio_context_sync(context);
+  }
+  howManyMain = 200;
+  howManyProc = 200;
 }
 
-void WebAudioWorkletThreadInitialized(EMSCRIPTEN_WEBAUDIO_T audioContext, bool success, void *userData) {
-  WebAudioWorkletProcessorCreateOptions opts = { .name = "noise-generator" };
-  emscripten_create_wasm_audio_worklet_processor_async(audioContext, &opts, AudioWorkletProcessorCreated, NULL);
+// HTML button to manually run the test
+EM_JS(void, addButton, (), {
+  var button = document.createElement("button");
+  button.appendChild(document.createTextNode("Start Test"));
+  document.body.appendChild(button);
+  document.onclick = () => {
+    if (globalThis._startTest) {
+      _startTest();
+    }
+  };
+});
+
+// Audio processor created, now register the audio callback
+void processorCreated(EMSCRIPTEN_WEBAUDIO_T ctx, bool success, void* data) {
+  assert(success && "Audio worklet failed in processorCreated()");
+  emscripten_out("Audio worklet processor created");
+  // Single stereo output
+  int outputChannelCounts[1] = { 1 };
+  EmscriptenAudioWorkletNodeCreateOptions opts = {
+    .numberOfOutputs = 1,
+    .outputChannelCounts = outputChannelCounts
+  };
+  EMSCRIPTEN_AUDIO_WORKLET_NODE_T worklet = emscripten_create_wasm_audio_worklet_node(ctx, "locks-test", &opts, &process, data);
+  emscripten_audio_node_connect(worklet, ctx, 0, 0);
 }
 
-uint8_t wasmAudioWorkletStack[2048];
+// Worklet thread inited, now create the audio processor
+void initialised(EMSCRIPTEN_WEBAUDIO_T ctx, bool success, void* data) {
+  assert(success && "Audio worklet failed in initialised()");
+  emscripten_out("Audio worklet initialised");
+  WebAudioWorkletProcessorCreateOptions opts = {
+    .name = "locks-test"
+  };
+  emscripten_create_wasm_audio_worklet_processor_async(ctx, &opts, &processorCreated, data);
+}
 
 int main() {
-  // Main thread init and acquire (work passes to the processor)
   emscripten_lock_init(&testLock);
-  int hasLock = emscripten_lock_busyspin_wait_acquire(&testLock, 0);
-  assert(hasLock);
-
-  startTime = emscripten_get_now();
-
-  emscripten_set_timeout_loop(MainLoop, 10, NULL);
-  EMSCRIPTEN_WEBAUDIO_T context = emscripten_create_audio_context(NULL);
-  emscripten_start_wasm_audio_worklet_thread_async(context, wasmAudioWorkletStack, sizeof(wasmAudioWorkletStack), WebAudioWorkletThreadInitialized, NULL);
+  Dummy* dummy = (Dummy*) malloc(sizeof(Dummy));
+  initDummy(dummy);
+
+  char* const workletStack = memalign(16, AUDIO_STACK_SIZE);
+  assert(workletStack);
+  // Audio processor callback setup
+  context = emscripten_create_audio_context(NULL);
+  assert(context);
+  emscripten_start_wasm_audio_worklet_thread_async(context, workletStack, AUDIO_STACK_SIZE, initialised, dummy);
+
+  emscripten_set_timeout_loop(mainLoop, 10, dummy);
+  addButton();
+  startTest(); // <-- May need a manual click to start
 
   emscripten_exit_with_live_runtime();
 }

From 21fcb014305ba69bebeba14691a20a188a39f6dd Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Thu, 4 Dec 2025 17:12:29 +0100
Subject: [PATCH 02/17] Minor tidy

---
 test/webaudio/audioworklet_emscripten_locks.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 90b2684d73058..f9787e7fe526a 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -10,11 +10,6 @@
 // - emscripten_lock_release()
 // - emscripten_get_now() in AW
 
-// Build with emcc -sAUDIO_WORKLET -sWASM_WORKERS -pthread -O1 -g -o index.html audioworklet_emscripten_locks.c
-
-// Values -1.5373, 77.2259, -251.4728
-// Values -0.9080, -42.4902, -250.6685
-
 // Marks a function to be kept in the Module and exposed to script (instead of adding to EXPORTED_FUNCTIONS)
 #ifndef KEEP_IN_MODULE
 #define KEEP_IN_MODULE __attribute__((used, visibility("default")))

From fceee8f492989d402501640158d0b1644013048c Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Thu, 4 Dec 2025 17:17:16 +0100
Subject: [PATCH 03/17] Minor tidy

---
 test/webaudio/audioworklet_emscripten_locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index f9787e7fe526a..5aeb4b1d0cecb 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -47,7 +47,7 @@ int howManyMain = 0;
 int howManyProc = 0;
 
 // Our dummy container
-typedef struct Dummy {
+typedef struct {
   uint32_t val0;
   uint32_t val1;
   uint32_t val2;

From 8f19d2b70af750f12749a2e73fa0248b7c8a4c95 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Thu, 4 Dec 2025 18:31:31 +0100
Subject: [PATCH 04/17] Should be flake-free

---
 test/test_browser.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/test/test_browser.py b/test/test_browser.py
index a50d5b89d0386..24b118a5f8ce2 100644
--- a/test/test_browser.py
+++ b/test/test_browser.py
@@ -5474,7 +5474,6 @@ def test_audio_worklet_params_mixing(self, args):
   @requires_sound_hardware
   @requires_shared_array_buffer
   @also_with_minimal_runtime
-  @flaky('https://github.com/emscripten-core/emscripten/issues/25245')
   def test_audio_worklet_emscripten_locks(self):
     self.btest_exit('webaudio/audioworklet_emscripten_locks.c', cflags=['-sAUDIO_WORKLET', '-sWASM_WORKERS', '-pthread'])
 

From 41391bd18f21ce7e23684ffaf3db682c576cd41e Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Thu, 4 Dec 2025 23:32:12 +0100
Subject: [PATCH 05/17] Lowered lock wait time

---
 test/webaudio/audioworklet_emscripten_locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 5aeb4b1d0cecb..21b97a8f36e36 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -67,7 +67,7 @@ void printDummy(Dummy* dummy) {
 // Run a simple calculation that will only be stable *if* all values are atomically updated
 void runCalcs(Dummy* dummy, int num) {
   for (int n = 0; n < num; n++) {
-    int have = emscripten_lock_busyspin_wait_acquire(&testLock, 100);
+    int have = emscripten_lock_busyspin_wait_acquire(&testLock, 10);
     assert(have);
     dummy->val0 += dummy->val1 * dummy->val2;
     dummy->val1 += dummy->val2 * dummy->val0;

From d3df687faff931090cadd836b268803638ef9ccb Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Fri, 5 Dec 2025 07:52:06 +0100
Subject: [PATCH 06/17] Something to re-run blocked CI

---
 test/webaudio/audioworklet_emscripten_locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 21b97a8f36e36..a3bf9638bd12e 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -165,7 +165,7 @@ EM_JS(void, addButton, (), {
 void processorCreated(EMSCRIPTEN_WEBAUDIO_T ctx, bool success, void* data) {
   assert(success && "Audio worklet failed in processorCreated()");
   emscripten_out("Audio worklet processor created");
-  // Single stereo output
+  // Single mono output
   int outputChannelCounts[1] = { 1 };
   EmscriptenAudioWorkletNodeCreateOptions opts = {
     .numberOfOutputs = 1,

From 1de67c710751084b73231133aceedc1881093455 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Fri, 5 Dec 2025 12:38:21 +0100
Subject: [PATCH 07/17] Improved symmetry

The test function is called approx. 200'000x from each thread.
---
 test/webaudio/audioworklet_emscripten_locks.c | 21 ++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index a3bf9638bd12e..36d56ecb413a7 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -18,6 +18,9 @@
 // This needs to be big enough for a stereo output (1024 with a 128 frame) + working stack
 #define AUDIO_STACK_SIZE 2048
 
+// Define DISABLE_LOCKS to run the test without locking, which should statistically always fail
+//#define DISABLE_LOCKS
+
 // Internal, found in 'system/lib/pthread/threading_internal.h' (and requires building with -pthread)
 int _emscripten_thread_supports_atomics_wait(void);
 
@@ -65,10 +68,13 @@ void printDummy(Dummy* dummy) {
 }
 
 // Run a simple calculation that will only be stable *if* all values are atomically updated
+// (Currently called approx. 200'000x from each thread)
 void runCalcs(Dummy* dummy, int num) {
   for (int n = 0; n < num; n++) {
+#ifndef DISABLE_LOCKS
     int have = emscripten_lock_busyspin_wait_acquire(&testLock, 10);
     assert(have);
+#endif
     dummy->val0 += dummy->val1 * dummy->val2;
     dummy->val1 += dummy->val2 * dummy->val0;
     dummy->val2 += dummy->val0 * dummy->val1;
@@ -80,7 +86,7 @@ void runCalcs(Dummy* dummy, int num) {
 }
 
 void stopping() {
-  emscripten_out("Expect: 949807601, 1303780836, 243502614");
+  emscripten_out("Expect: 811100370, 759556424, 723197652");
   emscripten_out("Ending test");
   emscripten_destroy_audio_context(context);
   emscripten_force_exit(0);
@@ -96,16 +102,16 @@ bool process(int numInputs, const AudioSampleFrame* inputs, int numOutputs, Audi
   case TEST_RUNNING:
   case TEST_DONE_MAIN:
     if (howManyProc-- > 0) {
-      runCalcs((Dummy*) data, 250);
+      runCalcs((Dummy*) data, 267); // <-- process gets called 3.75x more than main
     } else {
       if (whichTest == TEST_DONE_MAIN) {
+        emscripten_outf("Worklet done after %dms (expect: > 2s)", (int) (emscripten_get_now() - startTime));
         // Both loops are finished
         whichTest = TEST_DONE;
       }
     }
     break;
   case TEST_DONE:
-    emscripten_outf("Took %dms (expect: > 0)", (int) (emscripten_get_now() - startTime));
     return false;
   }
   return true;
@@ -121,6 +127,7 @@ bool mainLoop(double time, void* data) {
     if (howManyMain-- > 0) {
       runCalcs((Dummy*) data, 1000);
     } else {
+      emscripten_outf("Main thread done after %dms (expect: > 2s)", (int) (emscripten_get_now() - startTime));
       // Done here, so signal to process()
       whichTest = TEST_DONE_MAIN;
     }
@@ -131,9 +138,9 @@ bool mainLoop(double time, void* data) {
   case TEST_DONE:
     printDummy((Dummy*) data);
     // 32-bit maths with locks *should* result in these:
-    assert(((Dummy*) data)->val0 ==  949807601
-        && ((Dummy*) data)->val1 == 1303780836
-        && ((Dummy*) data)->val2 ==  243502614);
+    assert(((Dummy*) data)->val0 == 811100370
+        && ((Dummy*) data)->val1 == 759556424
+        && ((Dummy*) data)->val2 == 723197652);
     stopping();
     return false;
   }
@@ -146,7 +153,7 @@ KEEP_IN_MODULE void startTest() {
     emscripten_resume_audio_context_sync(context);
   }
   howManyMain = 200;
-  howManyProc = 200;
+  howManyProc = 750; // <-- process gets called 3.75x more than main
 }
 
 // HTML button to manually run the test

From 855e3bc9f7c81aabd64ac6ea3e3d4f3cf17dc1a4 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Fri, 5 Dec 2025 12:45:56 +0100
Subject: [PATCH 08/17] (Failure due to Firefox not downloading on CI)

---
 test/webaudio/audioworklet_emscripten_locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 36d56ecb413a7..f9459c3aa7844 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -68,7 +68,7 @@ void printDummy(Dummy* dummy) {
 }
 
 // Run a simple calculation that will only be stable *if* all values are atomically updated
-// (Currently called approx. 200'000x from each thread)
+// (Currently approx. 200'000x from each thread)
 void runCalcs(Dummy* dummy, int num) {
   for (int n = 0; n < num; n++) {
 #ifndef DISABLE_LOCKS

From 54815fa44cd0c5cd8d92ebc5f8d5844a30b6dd10 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Tue, 9 Dec 2025 10:50:53 +0100
Subject: [PATCH 09/17] Moved to EMSCRIPTEN_KEEPALIVE

---
 test/webaudio/audioworklet_emscripten_locks.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index f9459c3aa7844..998182f8a8029 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -10,11 +10,6 @@
 // - emscripten_lock_release()
 // - emscripten_get_now() in AW
 
-// Marks a function to be kept in the Module and exposed to script (instead of adding to EXPORTED_FUNCTIONS)
-#ifndef KEEP_IN_MODULE
-#define KEEP_IN_MODULE __attribute__((used, visibility("default")))
-#endif
-
 // This needs to be big enough for a stereo output (1024 with a 128 frame) + working stack
 #define AUDIO_STACK_SIZE 2048
 
@@ -147,7 +142,7 @@ bool mainLoop(double time, void* data) {
   return true;
 }
 
-KEEP_IN_MODULE void startTest() {
+EMSCRIPTEN_KEEPALIVE void startTest() {
   startTime = emscripten_get_now();
   if (emscripten_audio_context_state(context) != AUDIO_CONTEXT_STATE_RUNNING) {
     emscripten_resume_audio_context_sync(context);

From 798d1e27c61dc41f1da460f95a0074b2eb17e9bc Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Tue, 9 Dec 2025 11:26:00 +0100
Subject: [PATCH 10/17] Removed magic numbers

---
 test/webaudio/audioworklet_emscripten_locks.c | 30 +++++++++----------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 998182f8a8029..5ceefbecf0a3f 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -14,7 +14,7 @@
 #define AUDIO_STACK_SIZE 2048
 
 // Define DISABLE_LOCKS to run the test without locking, which should statistically always fail
-//#define DISABLE_LOCKS
+#define DISABLE_LOCKS
 
 // Internal, found in 'system/lib/pthread/threading_internal.h' (and requires building with -pthread)
 int _emscripten_thread_supports_atomics_wait(void);
@@ -53,13 +53,13 @@ typedef struct {
 
 // Start values
 void initDummy(Dummy* dummy) {
-  dummy->val0 = 4;
+  dummy->val0 = 1;
   dummy->val1 = 1;
-  dummy->val2 = 2;
+  dummy->val2 = 1;
 }
 
 void printDummy(Dummy* dummy) {
-  emscripten_outf("Values: %u, %u, %u", dummy->val0, dummy->val1, dummy->val2);
+  emscripten_outf("Values: 0x%08X, 0x%08X, 0x%08X", dummy->val0, dummy->val1, dummy->val2);
 }
 
 // Run a simple calculation that will only be stable *if* all values are atomically updated
@@ -70,18 +70,20 @@ void runCalcs(Dummy* dummy, int num) {
     int have = emscripten_lock_busyspin_wait_acquire(&testLock, 10);
     assert(have);
 #endif
-    dummy->val0 += dummy->val1 * dummy->val2;
-    dummy->val1 += dummy->val2 * dummy->val0;
-    dummy->val2 += dummy->val0 * dummy->val1;
-    dummy->val0 /= 4;
-    dummy->val1 /= 3;
-    dummy->val2 /= 2;
+    dummy->val0 += dummy->val2 * 7;
+    dummy->val1 += dummy->val0 * 7;
+    dummy->val2 += dummy->val1 * 7;
+    dummy->val0 += dummy->val2 / 3;
+    dummy->val1 += dummy->val0 / 3;
+    dummy->val2 += dummy->val1 / 3;
+#ifndef DISABLE_LOCKS
     emscripten_lock_release(&testLock);
+#endif
   }
 }
 
 void stopping() {
-  emscripten_out("Expect: 811100370, 759556424, 723197652");
+  emscripten_out("Expect: all values are equal");
   emscripten_out("Ending test");
   emscripten_destroy_audio_context(context);
   emscripten_force_exit(0);
@@ -132,10 +134,8 @@ bool mainLoop(double time, void* data) {
     break;
   case TEST_DONE:
     printDummy((Dummy*) data);
-    // 32-bit maths with locks *should* result in these:
-    assert(((Dummy*) data)->val0 == 811100370
-        && ((Dummy*) data)->val1 == 759556424
-        && ((Dummy*) data)->val2 == 723197652);
+    assert(((Dummy*) data)->val0 == ((Dummy*) data)->val1
+        && ((Dummy*) data)->val1 == ((Dummy*) data)->val2);
     stopping();
     return false;
   }

From ce9d8662f5df733ca43b9c0a2bd9f3109b9f5f27 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Tue, 9 Dec 2025 11:30:44 +0100
Subject: [PATCH 11/17] Re-enabled locks

---
 test/webaudio/audioworklet_emscripten_locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 5ceefbecf0a3f..f0bc7537979e6 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -14,7 +14,7 @@
 #define AUDIO_STACK_SIZE 2048
 
 // Define DISABLE_LOCKS to run the test without locking, which should statistically always fail
-#define DISABLE_LOCKS
+//#define DISABLE_LOCKS
 
 // Internal, found in 'system/lib/pthread/threading_internal.h' (and requires building with -pthread)
 int _emscripten_thread_supports_atomics_wait(void);

From 0c54c71bcfade7da4759fc9fc1f91076e76db939 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Tue, 9 Dec 2025 12:30:45 +0100
Subject: [PATCH 12/17] Revert "Removed magic numbers"

This reverts commit 5677c957993a6e4d326288760b9c33688ac0ac26.
---
 test/webaudio/audioworklet_emscripten_locks.c | 28 +++++++++----------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index f0bc7537979e6..998182f8a8029 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -53,13 +53,13 @@ typedef struct {
 
 // Start values
 void initDummy(Dummy* dummy) {
-  dummy->val0 = 1;
+  dummy->val0 = 4;
   dummy->val1 = 1;
-  dummy->val2 = 1;
+  dummy->val2 = 2;
 }
 
 void printDummy(Dummy* dummy) {
-  emscripten_outf("Values: 0x%08X, 0x%08X, 0x%08X", dummy->val0, dummy->val1, dummy->val2);
+  emscripten_outf("Values: %u, %u, %u", dummy->val0, dummy->val1, dummy->val2);
 }
 
 // Run a simple calculation that will only be stable *if* all values are atomically updated
@@ -70,20 +70,18 @@ void runCalcs(Dummy* dummy, int num) {
     int have = emscripten_lock_busyspin_wait_acquire(&testLock, 10);
     assert(have);
 #endif
-    dummy->val0 += dummy->val2 * 7;
-    dummy->val1 += dummy->val0 * 7;
-    dummy->val2 += dummy->val1 * 7;
-    dummy->val0 += dummy->val2 / 3;
-    dummy->val1 += dummy->val0 / 3;
-    dummy->val2 += dummy->val1 / 3;
-#ifndef DISABLE_LOCKS
+    dummy->val0 += dummy->val1 * dummy->val2;
+    dummy->val1 += dummy->val2 * dummy->val0;
+    dummy->val2 += dummy->val0 * dummy->val1;
+    dummy->val0 /= 4;
+    dummy->val1 /= 3;
+    dummy->val2 /= 2;
     emscripten_lock_release(&testLock);
-#endif
   }
 }
 
 void stopping() {
-  emscripten_out("Expect: all values are equal");
+  emscripten_out("Expect: 811100370, 759556424, 723197652");
   emscripten_out("Ending test");
   emscripten_destroy_audio_context(context);
   emscripten_force_exit(0);
@@ -134,8 +132,10 @@ bool mainLoop(double time, void* data) {
     break;
   case TEST_DONE:
     printDummy((Dummy*) data);
-    assert(((Dummy*) data)->val0 == ((Dummy*) data)->val1
-        && ((Dummy*) data)->val1 == ((Dummy*) data)->val2);
+    // 32-bit maths with locks *should* result in these:
+    assert(((Dummy*) data)->val0 == 811100370
+        && ((Dummy*) data)->val1 == 759556424
+        && ((Dummy*) data)->val2 == 723197652);
     stopping();
     return false;
   }

From 868f5b3a3db2407ac819e566aa8eed81fd22a236 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Tue, 9 Dec 2025 12:36:00 +0100
Subject: [PATCH 13/17] Minor tidy

---
 test/webaudio/audioworklet_emscripten_locks.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 998182f8a8029..5dfdb63b70e46 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -59,7 +59,7 @@ void initDummy(Dummy* dummy) {
 }
 
 void printDummy(Dummy* dummy) {
-  emscripten_outf("Values: %u, %u, %u", dummy->val0, dummy->val1, dummy->val2);
+  emscripten_outf("Values: 0x%08X, 0x%08X, 0x%08X", dummy->val0, dummy->val1, dummy->val2);
 }
 
 // Run a simple calculation that will only be stable *if* all values are atomically updated
@@ -76,12 +76,14 @@ void runCalcs(Dummy* dummy, int num) {
     dummy->val0 /= 4;
     dummy->val1 /= 3;
     dummy->val2 /= 2;
+#ifndef DISABLE_LOCKS
     emscripten_lock_release(&testLock);
+#endif
   }
 }
 
 void stopping() {
-  emscripten_out("Expect: 811100370, 759556424, 723197652");
+  emscripten_out("Expect: 0x305868D2, 0x2D45E948, 0x2B1B1ED4");
   emscripten_out("Ending test");
   emscripten_destroy_audio_context(context);
   emscripten_force_exit(0);
@@ -133,9 +135,9 @@ bool mainLoop(double time, void* data) {
   case TEST_DONE:
     printDummy((Dummy*) data);
     // 32-bit maths with locks *should* result in these:
-    assert(((Dummy*) data)->val0 == 811100370
-        && ((Dummy*) data)->val1 == 759556424
-        && ((Dummy*) data)->val2 == 723197652);
+    assert(((Dummy*) data)->val0 == 0x305868D2
+        && ((Dummy*) data)->val1 == 0x2D45E948
+        && ((Dummy*) data)->val2 == 0x2B1B1ED4);
     stopping();
     return false;
   }

From dd7c0bd2f81970e0c39f66d6fd7435298361fbd2 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Tue, 9 Dec 2025 17:30:15 +0100
Subject: [PATCH 14/17] Pre-calculate magic numbers

---
 test/webaudio/audioworklet_emscripten_locks.c | 52 +++++++++++++------
 1 file changed, 37 insertions(+), 15 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 5dfdb63b70e46..0457ad0442acc 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -14,7 +14,16 @@
 #define AUDIO_STACK_SIZE 2048
 
 // Define DISABLE_LOCKS to run the test without locking, which should statistically always fail
-//#define DISABLE_LOCKS
+#define DISABLE_LOCKS
+
+// Number of times mainLoop() calculations get called
+#define MAINLOOP_CALCS 10000
+// Number of times MAINLOOP_CALCS are performed
+#define MAINLOOP_RUNS 200
+// Number of times process() calculations get called (called 3.75x more than mainLoop)
+#define PROCESS_CALCS 2667
+// Number of times PROCESS_CALCS are performed (3.75x more than mainLoop)
+#define PROCESS_RUNS 750
 
 // Internal, found in 'system/lib/pthread/threading_internal.h' (and requires building with -pthread)
 int _emscripten_thread_supports_atomics_wait(void);
@@ -51,6 +60,11 @@ typedef struct {
   uint32_t val2;
 } Dummy;
 
+// Container used to run the test
+Dummy testData;
+// Container to hold the expected value
+Dummy trueData;
+
 // Start values
 void initDummy(Dummy* dummy) {
   dummy->val0 = 4;
@@ -83,8 +97,7 @@ void runCalcs(Dummy* dummy, int num) {
 }
 
 void stopping() {
-  emscripten_out("Expect: 0x305868D2, 0x2D45E948, 0x2B1B1ED4");
-  emscripten_out("Ending test");
+  emscripten_out("Test done");
   emscripten_destroy_audio_context(context);
   emscripten_force_exit(0);
 }
@@ -99,7 +112,7 @@ bool process(int numInputs, const AudioSampleFrame* inputs, int numOutputs, Audi
   case TEST_RUNNING:
   case TEST_DONE_MAIN:
     if (howManyProc-- > 0) {
-      runCalcs((Dummy*) data, 267); // <-- process gets called 3.75x more than main
+      runCalcs((Dummy*) data, PROCESS_CALCS);
     } else {
       if (whichTest == TEST_DONE_MAIN) {
         emscripten_outf("Worklet done after %dms (expect: > 2s)", (int) (emscripten_get_now() - startTime));
@@ -122,7 +135,7 @@ bool mainLoop(double time, void* data) {
     break;
   case TEST_RUNNING:
     if (howManyMain-- > 0) {
-      runCalcs((Dummy*) data, 1000);
+      runCalcs((Dummy*) data, MAINLOOP_CALCS);
     } else {
       emscripten_outf("Main thread done after %dms (expect: > 2s)", (int) (emscripten_get_now() - startTime));
       // Done here, so signal to process()
@@ -133,11 +146,11 @@ bool mainLoop(double time, void* data) {
     // Wait for process() to finish
     break;
   case TEST_DONE:
+    emscripten_out("Multi-thread results:");
     printDummy((Dummy*) data);
-    // 32-bit maths with locks *should* result in these:
-    assert(((Dummy*) data)->val0 == 0x305868D2
-        && ((Dummy*) data)->val1 == 0x2D45E948
-        && ((Dummy*) data)->val2 == 0x2B1B1ED4);
+    assert(((Dummy*) data)->val0 == trueData.val0
+        && ((Dummy*) data)->val1 == trueData.val1
+        && ((Dummy*) data)->val2 == trueData.val2);
     stopping();
     return false;
   }
@@ -149,8 +162,8 @@ EMSCRIPTEN_KEEPALIVE void startTest() {
   if (emscripten_audio_context_state(context) != AUDIO_CONTEXT_STATE_RUNNING) {
     emscripten_resume_audio_context_sync(context);
   }
-  howManyMain = 200;
-  howManyProc = 750; // <-- process gets called 3.75x more than main
+  howManyMain = MAINLOOP_RUNS;
+  howManyProc = PROCESS_RUNS;
 }
 
 // HTML button to manually run the test
@@ -191,17 +204,26 @@ void initialised(EMSCRIPTEN_WEBAUDIO_T ctx, bool success, void* data) {
 
 int main() {
   emscripten_lock_init(&testLock);
-  Dummy* dummy = (Dummy*) malloc(sizeof(Dummy));
-  initDummy(dummy);
+  initDummy(&testData);
+  initDummy(&trueData);
+  // Canonical results, run in a single thread
+  for (int n = MAINLOOP_RUNS; n > 0; n--) {
+    runCalcs(&trueData, MAINLOOP_CALCS);
+  }
+  for (int n = PROCESS_RUNS; n > 0; n--) {
+    runCalcs(&trueData, PROCESS_CALCS);
+  }
+  emscripten_out("Single-thread results:");
+  printDummy(&trueData);
 
   char* const workletStack = memalign(16, AUDIO_STACK_SIZE);
   assert(workletStack);
   // Audio processor callback setup
   context = emscripten_create_audio_context(NULL);
   assert(context);
-  emscripten_start_wasm_audio_worklet_thread_async(context, workletStack, AUDIO_STACK_SIZE, initialised, dummy);
+  emscripten_start_wasm_audio_worklet_thread_async(context, workletStack, AUDIO_STACK_SIZE, initialised, &testData);
 
-  emscripten_set_timeout_loop(mainLoop, 10, dummy);
+  emscripten_set_timeout_loop(mainLoop, 10, &testData);
   addButton();
   startTest(); // <-- May need a manual click to start
 

From 1e9ab3a3890533f73f65b977ae4f7a0d814649b4 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Tue, 9 Dec 2025 17:30:38 +0100
Subject: [PATCH 15/17] Ahem, re-enable locks

---
 test/webaudio/audioworklet_emscripten_locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 0457ad0442acc..29af77c936e42 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -14,7 +14,7 @@
 #define AUDIO_STACK_SIZE 2048
 
 // Define DISABLE_LOCKS to run the test without locking, which should statistically always fail
-#define DISABLE_LOCKS
+//#define DISABLE_LOCKS
 
 // Number of times mainLoop() calculations get called
 #define MAINLOOP_CALCS 10000

From 29097a520587c87751c5a776dd8e38df93e1ffd4 Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Wed, 10 Dec 2025 00:23:00 +0100
Subject: [PATCH 16/17] Very, very long lock acquire wait (for slower CI)

---
 test/webaudio/audioworklet_emscripten_locks.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 29af77c936e42..490ef64bcf434 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -81,7 +81,7 @@ void printDummy(Dummy* dummy) {
 void runCalcs(Dummy* dummy, int num) {
   for (int n = 0; n < num; n++) {
 #ifndef DISABLE_LOCKS
-    int have = emscripten_lock_busyspin_wait_acquire(&testLock, 10);
+    int have = emscripten_lock_busyspin_wait_acquire(&testLock, 1000);
     assert(have);
 #endif
     dummy->val0 += dummy->val1 * dummy->val2;

From 5c2641b1d358b2ccd375e8008c8e057d3545c09c Mon Sep 17 00:00:00 2001
From: Carl Woffenden <cwoffenden@gmail.com>
Date: Wed, 10 Dec 2025 15:26:46 +0100
Subject: [PATCH 17/17] Clarified text

---
 test/webaudio/audioworklet_emscripten_locks.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/test/webaudio/audioworklet_emscripten_locks.c b/test/webaudio/audioworklet_emscripten_locks.c
index 490ef64bcf434..56aee3bdb88f4 100644
--- a/test/webaudio/audioworklet_emscripten_locks.c
+++ b/test/webaudio/audioworklet_emscripten_locks.c
@@ -115,7 +115,7 @@ bool process(int numInputs, const AudioSampleFrame* inputs, int numOutputs, Audi
       runCalcs((Dummy*) data, PROCESS_CALCS);
     } else {
       if (whichTest == TEST_DONE_MAIN) {
-        emscripten_outf("Worklet done after %dms (expect: > 2s)", (int) (emscripten_get_now() - startTime));
+        emscripten_outf("Worklet done after %dms (expect: approx. 2s)", (int) (emscripten_get_now() - startTime));
         // Both loops are finished
         whichTest = TEST_DONE;
       }
@@ -137,7 +137,7 @@ bool mainLoop(double time, void* data) {
     if (howManyMain-- > 0) {
       runCalcs((Dummy*) data, MAINLOOP_CALCS);
     } else {
-      emscripten_outf("Main thread done after %dms (expect: > 2s)", (int) (emscripten_get_now() - startTime));
+      emscripten_outf("Main thread done after %dms (expect: approx. 2s)", (int) (emscripten_get_now() - startTime));
       // Done here, so signal to process()
       whichTest = TEST_DONE_MAIN;
     }