[JSPI] Automatically add promising JSPI wrappers to thread entry points. (emscripten-core#22891)

Use a WebAssembly.Promising wrapper on the thread entry points to allow
JSPI to be used from worker threads. The code that invokes the wrapper
also adds async/await to handle this async call to entry point.

Fixes emscripten-core#22354

---------

Co-authored-by: Alon Zakai <[email protected]>

Author: 2 people

src/library_pthread.js

@@ -1043,7 +1043,7 @@ var LibraryPThread = {
     '$runtimeKeepaliveCounter',
 #endif
   ],
-  $invokeEntryPoint: (ptr, arg) => {
+  $invokeEntryPoint: {{{ asyncIf(ASYNCIFY == 2) }}} (ptr, arg) => {
 #if PTHREADS_DEBUG
     dbg(`invokeEntryPoint: ${ptrToString(ptr)}`);
 #endif
@@ -1079,7 +1079,9 @@ var LibraryPThread = {
     // *ThreadMain(void *arg) form, or try linking with the Emscripten linker
     // flag -sEMULATE_FUNCTION_POINTER_CASTS to add in emulation for this x86
     // ABI extension.
-    var result = {{{ makeDynCall('pp', 'ptr') }}}(arg);
+
+    var result = {{{ makeDynCall('pp', 'ptr', ASYNCIFY == 2) }}}(arg);
+
 #if STACK_OVERFLOW_CHECK
     checkStackCookie();
 #endif
@@ -1098,10 +1100,9 @@ var LibraryPThread = {
 #endif
     }
 #if ASYNCIFY == 2
-    Promise.resolve(result).then(finish);
-#else
-    finish(result);
+    result = await result;
 #endif
+    finish(result);
   },
 
 #if MAIN_MODULE

src/parseTools.mjs

@@ -597,11 +597,12 @@ function charCode(char) {
   return char.charCodeAt(0);
 }
 
-function makeDynCall(sig, funcPtr) {
+function makeDynCall(sig, funcPtr, promising = false) {
   assert(
     !sig.includes('j'),
     'Cannot specify 64-bit signatures ("j" in signature string) with makeDynCall!',
   );
+  assert(!(DYNCALLS && promising), 'DYNCALLS cannot be used with JSPI.');
 
   let args = [];
   for (let i = 1; i < sig.length; ++i) {
@@ -672,10 +673,15 @@ Please update to new syntax.`);
     return `(() => ${dyncall}(${funcPtr}))`;
   }
 
+  let getWasmTableEntry = `getWasmTableEntry(${funcPtr})`;
+  if (promising) {
+    getWasmTableEntry = `WebAssembly.promising(${getWasmTableEntry})`;
+  }
+
   if (needArgConversion) {
-    return `((${args}) => getWasmTableEntry(${funcPtr}).call(null, ${callArgs}))`;
+    return `((${args}) => ${getWasmTableEntry}.call(null, ${callArgs}))`;
   }
-  return `getWasmTableEntry(${funcPtr})`;
+  return getWasmTableEntry;
 }
 
 function makeEval(code) {

src/runtime_pthread.js

@@ -66,7 +66,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
   // notified about them.
   self.onunhandledrejection = (e) => { throw e.reason || e; };
 
-  function handleMessage(e) {
+  {{{ asyncIf(ASYNCIFY == 2) }}} function handleMessage(e) {
     try {
       var msgData = e['data'];
       //dbg('msgData: ' + Object.keys(msgData));
@@ -177,7 +177,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
         }
 
         try {
-          invokeEntryPoint(msgData.start_routine, msgData.arg);
+          {{{ awaitIf(ASYNCIFY == 2) }}} invokeEntryPoint(msgData.start_routine, msgData.arg);
         } catch(ex) {
           if (ex != 'unwind') {
             // The pthread "crashed".  Do not call `_emscripten_thread_exit` (which

test/core/test_pthread_join_and_asyncify.c

@@ -13,15 +13,17 @@ EM_ASYNC_JS(int, async_call, (), {
   return 42;
 });
 
-// TODO Remove EMSCRIPTEN_KEEPALIVE when support for async attributes is enabled.
-EMSCRIPTEN_KEEPALIVE void *run_thread(void *args) {
+void *run_thread(void *args) {
   int ret = async_call();
   assert(ret == 42);
   return NULL;
 }
 
 int main() {
   pthread_t id;
+  // Test that JSPI works on the main thread.
+  emscripten_sleep(1);
+  // Also test that JSPI works on other threads.
   pthread_create(&id, NULL, run_thread, NULL);
   printf("joining thread!\n");
   pthread_join(id, NULL);

test/test_core.py

@@ -8312,7 +8312,7 @@ def test_pthread_join_and_asyncify(self):
     # TODO Test with ASYNCIFY=1 https://github.com/emscripten-core/emscripten/issues/17552
     self.require_jspi()
     self.do_runf('core/test_pthread_join_and_asyncify.c', 'joining thread!\njoined thread!',
-                 emcc_args=['-sJSPI_EXPORTS=run_thread',
+                 emcc_args=['-sJSPI',
                             '-sEXIT_RUNTIME=1',
                             '-pthread', '-sPROXY_TO_PTHREAD'])