Enable emscripten_futex API for wasm workers

This involves also including `emscripten_thread_state.S` which provides
APIs such as `emscripten_is_main_runtime_thread` and
emscripten_is_main_browser_thread` which now also work in Wasm Workers.

There is a minor code size hit here of ~80 bytes, but I think its
worth it to have these low level APIs available everywhere.

Author: sbc100

src/lib/libwasm_worker.js

@@ -93,9 +93,7 @@ addToLibrary({
     '$_wasmWorkerRunPostMessage',
     '$_wasmWorkerAppendToQueue',
     '_emscripten_wasm_worker_initialize',
-#if PTHREADS
     '__set_thread_state',
-#endif
   ],
   $_wasmWorkerInitializeRuntime: () => {
 #if ASSERTIONS
@@ -126,11 +124,9 @@ addToLibrary({
 #endif
     // Run the C side Worker initialization for stack and TLS.
     __emscripten_wasm_worker_initialize(wwParams.stackLowestAddress, wwParams.stackSize);
-#if PTHREADS
-    // Record the pthread configuration, and whether this Wasm Worker supports synchronous blocking in emscripten_futex_wait().
+    // Record low level information.  Now all Wasm Workers support synchronous blocking in emscripten_futex_wait().
     // (regular Wasm Workers do, AudioWorklets don't)
     ___set_thread_state(/*thread_ptr=*/0, /*is_main_thread=*/0, /*is_runtime_thread=*/0, /*supports_wait=*/ {{{ workerSupportsFutexWait() }}});
-#endif
 #if STACK_OVERFLOW_CHECK >= 2
     // Fix up stack base. (TLS frame is created at the bottom address end of the stack)
     // See https://github.com/emscripten-core/emscripten/issues/16496
@@ -342,5 +338,17 @@ if (ENVIRONMENT_IS_WASM_WORKER
       else dispatch(-1/*idx*/, 2/*'timed-out'*/);
     };
     tryAcquireSemaphore();
-  }
+  },
+
+  _emscripten_init_main_thread_js__deps: ['__set_thread_state'],
+  _emscripten_init_main_thread_js: (tb) => {
+    // Pass the thread address to the native code where they are stored in wasm
+    // globals which act as a form of TLS. Global constructors trying
+    // to access this value will read the wrong value, but that is UB anyway.
+    ___set_thread_state(
+      /*thread_ptr=*/0,
+      /*is_main_thread=*/!ENVIRONMENT_IS_WORKER,
+      /*is_runtime_thread=*/1,
+      /*supports_wait=*/!ENVIRONMENT_IS_WEB);
+  },
 });

src/shell_minimal.js

@@ -39,7 +39,7 @@ var ENVIRONMENT_IS_NODE = {{{ nodeDetectionCode() }}};
 var ENVIRONMENT_IS_SHELL = !!globalThis.read;
 #endif
 
-#if ASSERTIONS || PTHREADS
+#if ASSERTIONS || PTHREADS || WASM_WORKERS
 #if !ENVIRONMENT_MAY_BE_NODE && !ENVIRONMENT_MAY_BE_SHELL
 var ENVIRONMENT_IS_WEB = true
 #elif ENVIRONMENT.length == 1

system/include/emscripten/threading.h

@@ -42,11 +42,13 @@ int emscripten_futex_wake(volatile void/*uint32_t*/ * _Nonnull addr, int count);
 
 // Returns true if the current thread is the thread that hosts the Emscripten
 // runtime.
+// Returns false on pthreads and Wasm Workers.
 bool emscripten_is_main_runtime_thread(void);
 
 // Returns true if the current thread is the main browser thread.  In the case
 // that the Emscripten module is started in a worker there will be no thread
 // for which this returns true.
+// Returns false on pthreads and Wasm Workers.
 bool emscripten_is_main_browser_thread(void);
 
 // A temporary workaround to issue

system/lib/pthread/library_pthread_stub.c

@@ -21,6 +21,10 @@ bool emscripten_has_threading_support() { return false; }
 
 int emscripten_num_logical_cores() { return 1; }
 
+#ifndef __EMSCRIPTEN_WASM_WORKERS__
+// These low level primites are defined in both pthreads and wasm workers
+// builds.
+
 int emscripten_futex_wait(volatile void /*uint32_t*/* addr,
                           uint32_t val,
                           double maxWaitMilliseconds) {
@@ -39,10 +43,20 @@ int emscripten_futex_wake(volatile void /*uint32_t*/* addr, int count) {
 }
 
 bool emscripten_is_main_runtime_thread() {
-  // TODO: We probably shouldn't be returning true here in WASM_WORKERS builds.
   return true;
 }
 
+void __wait(volatile int *addr, volatile int *waiters, int val, int priv) {}
+
+void __lock(void* ptr) {}
+
+void __unlock(void* ptr) {}
+
+void __acquire_ptc() {}
+
+void __release_ptc() {}
+#endif
+
 void emscripten_main_thread_process_queued_calls() {
   // nop
 }
@@ -385,16 +399,6 @@ int sem_destroy(sem_t *sem) {
   return 0;
 }
 
-void __wait(volatile int *addr, volatile int *waiters, int val, int priv) {}
-
-void __lock(void* ptr) {}
-
-void __unlock(void* ptr) {}
-
-void __acquire_ptc() {}
-
-void __release_ptc() {}
-
 // When pthreads is not enabled, we can't use the Atomics futex api to do
 // proper sleeps, so simulate a busy spin wait loop instead.
 void emscripten_thread_sleep(double msecs) {

system/lib/wasm_worker/library_wasm_worker.c

@@ -223,3 +223,12 @@ void emscripten_condvar_signal(emscripten_condvar_t *condvar, int64_t numWaiters
   emscripten_atomic_add_u32((void*)condvar, 1);
   emscripten_atomic_notify((int*)condvar, numWaitersToSignal);
 }
+
+void _emscripten_init_main_thread_js(void* tb);
+
+// See system/lib/README.md for static constructor ordering.
+// See corresponding definition in library_pthread.c.
+__attribute__((constructor(48)))
+void _emscripten_init_main_thread(void) {
+  _emscripten_init_main_thread_js(NULL);
+}