Improve emscripten_futex_wait stub. NFC

system/lib/pthread/library_pthread_stub.c

@@ -21,18 +21,27 @@ int emscripten_has_threading_support() { return 0; }
 
 int emscripten_num_logical_cores() { return 1; }
 
-int emscripten_futex_wait(
-  volatile void /*uint32_t*/* addr, uint32_t val, double maxWaitMilliseconds) {
-  // nop
-  return 0; // success
+int emscripten_futex_wait(volatile void /*uint32_t*/* addr,
+                          uint32_t val,
+                          double maxWaitMilliseconds) {
+  if (!addr) {
+    return -EINVAL;
+  }
+  if (*(uint32_t*)addr != val) {
+    return -EWOULDBLOCK;
+  }
+  return -ENOTSUP;
 }
 
 int emscripten_futex_wake(volatile void /*uint32_t*/* addr, int count) {
   // nop
   return 0; // success
 }
 
-int emscripten_is_main_runtime_thread() { return 1; }
+int emscripten_is_main_runtime_thread() {
+  // TODO: We probably shouldn't be returning 1 here in WASM_WORKERS builds.
+  return 1;
+}
 
 void emscripten_main_thread_process_queued_calls() {
   // nop

test/codesize/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
   "a.out.js": 244691,
-  "a.out.nodebug.wasm": 577678,
-  "total": 822369,
+  "a.out.nodebug.wasm": 577699,
+  "total": 822390,
   "sent": [
     "IMG_Init",
     "IMG_Load",

test/test_browser.py

@@ -5039,9 +5039,11 @@ def test_wasm_worker_hello_wasm2js(self):
   def test_wasm_worker_hello_embedded(self):
     self.btest_exit('wasm_worker/hello_wasm_worker.c', cflags=['-sWASM_WORKERS=2'])
 
-  # Tests that it is possible to call emscripten_futex_wait() in Wasm Workers.
+  # Tests that it is possible to call emscripten_futex_wait() in Wasm Workers when pthreads
+  # are also enabled.
   @parameterized({
-    '': ([],),
+    # Without pthreads we expect the stub version of the futex API
+    '': (['-DEXPECT_STUB'],),
     'pthread': (['-pthread'],),
   })
   def test_wasm_worker_futex_wait(self, args):

test/wasm_worker/wasm_worker_futex_wait.c

@@ -1,5 +1,7 @@
 // Test that emscripten_futex_wait() works in a Wasm Worker.
 
+#include <assert.h>
+#include <errno.h>
 #include <emscripten.h>
 #include <emscripten/console.h>
 #include <emscripten/threading.h>
@@ -12,21 +14,37 @@ _Atomic uint32_t futex_value = 0;
 
 void wake_worker_after_delay(void *user_data) {
   futex_value = 1;
-  emscripten_futex_wake(&futex_value, INT_MAX);  
+  emscripten_futex_wake(&futex_value, INT_MAX);
 }
 
 void wake_worker() {
-  printf("Waking worker thread from futex wait.\n");
+  printf("Waking worker thread from futex wait...\n");
   emscripten_set_timeout(wake_worker_after_delay, 500, 0);
 }
 
 void worker_main() {
-  printf("Worker sleeping for futex wait.\n");
+  printf("Worker sleeping on futex...\n");
+  double start = emscripten_performance_now();
+  int rc = emscripten_futex_wait(&futex_value, 0, 100);
+  double end = emscripten_performance_now();
+  printf("emscripten_futex_wait returned: %d after %.2fms\n", rc, end - start);
+#if EXPECT_STUB
+  // The stub implemenation returns -ENOTSUP
+  assert(rc == -ENOTSUP);
+#else
+  assert(rc == -ETIMEDOUT);
+  assert((end - start) >= 100);
+
+  printf("Worker sleeping on futex with wakeup...\n");
   emscripten_wasm_worker_post_function_v(0, wake_worker);
-  int rc = emscripten_futex_wait(&futex_value, 0, INFINITY);
-  printf("emscripten_futex_wait returned with code %d.\n", rc);
+  rc = emscripten_futex_wait(&futex_value, 0, INFINITY);
+  printf("emscripten_futex_wait returned: %d\n", rc);
+  assert(rc == 0);
+  assert(futex_value == 1);
+#endif
+
 #ifdef REPORT_RESULT
-  REPORT_RESULT(rc);
+  REPORT_RESULT(0);
 #endif
 }
 

test/webaudio/audioworklet_worker.c

@@ -2,14 +2,14 @@
 #include <emscripten/wasm_worker.h>
 #include <emscripten/threading.h>
 #include <assert.h>
+#include <stdbool.h>
 
 // Tests that
 // - audioworklets and workers can be used at the same time.
 // - an audioworklet can emscripten_futex_wake() a waiting worker.
 // - global values can be shared between audioworklets and workers.
 
-int workletToWorkerFutexLocation = 0;
-int workletToWorkerFlag = 0;
+_Atomic bool workletToWorkerFlag = false;
 EMSCRIPTEN_WEBAUDIO_T context;
 
 void do_exit() {
@@ -19,8 +19,10 @@ void do_exit() {
 }
 
 void run_in_worker() {
-  while (0 == emscripten_futex_wait(&workletToWorkerFutexLocation, 0, 30000)) {
-    if (workletToWorkerFlag == 1) {
+  // TODO: Convert to emscripten_futex_wait once it becomes available in Wasm
+  // Workers.
+  while (1) {
+    if (workletToWorkerFlag == true) {
       emscripten_out("Test success");
       emscripten_wasm_worker_post_function_v(EMSCRIPTEN_WASM_WORKER_ID_PARENT, &do_exit);
       break;
@@ -31,8 +33,7 @@ void run_in_worker() {
 // This event will fire on the audio worklet thread.
 void MessageReceivedInAudioWorkletThread() {
   assert(emscripten_current_thread_is_audio_worklet());
-  workletToWorkerFlag = 1;
-  emscripten_futex_wake(&workletToWorkerFutexLocation, 1);
+  workletToWorkerFlag = true;
 }
 
 void WebAudioWorkletThreadInitialized(EMSCRIPTEN_WEBAUDIO_T audioContext, bool success, void *userData) {