[JSPI] Fix PROXY_TO_PTHREAD when used with JSPI.

Use a WebAssembly.Promising wrapper on the function that calls main
to allow JSPI to be used from the main (worker) thread. The code that
invokes the wrapper also adds async/await to handle this async call to
main.

Fixes #22354

Author: brendandahl

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 +1079,11 @@ 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.
+#if ASYNCIFY == 2
+    var result = WebAssembly.promising({{{ makeDynCall('pp', 'ptr') }}})(arg);
+#else
     var result = {{{ makeDynCall('pp', 'ptr') }}}(arg);
+#endif
 #if STACK_OVERFLOW_CHECK
     checkStackCookie();
 #endif
@@ -1098,10 +1102,9 @@ var LibraryPThread = {
 #endif
     }
 #if ASYNCIFY == 2
-    Promise.resolve(result).then(finish);
-#else
-    finish(result);
+    result = await result;
 #endif
+    finish(result);
   },
 
 #if MAIN_MODULE

src/runtime_pthread.js

@@ -90,7 +90,7 @@ 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));
@@ -201,7 +201,7 @@ 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/test_other.py

@@ -3316,6 +3316,20 @@ def test_jspi_add_function(self):
       '-Wno-experimental']
     self.do_runf('other/test_jspi_add_function.c', 'done')
 
+  @requires_node_canary
+  @requires_jspi
+  def test_jspi_proxy_to_pthread(self):
+    create_file('main.c', r'''
+#include <stdio.h>
+#include <emscripten/emscripten.h>
+int main() {
+  emscripten_sleep(1);
+  printf("ok\n");
+}
+''')
+    self.do_runf('main.c', 'ok',
+                 emcc_args=['-sJSPI', '-pthread', '-sPROXY_TO_PTHREAD', '-sEXIT_RUNTIME'])
+
   @parameterized({
     '': [[]],
     'with_jsgen': [['-sEMBIND_AOT']]