capture promise returned value

Author: hedwigz

src/library.js

@@ -1647,9 +1647,6 @@ addToLibrary({
       return proxyToMainThread(0, emAsmAddr, sync, promise, ...args);
     }
 #endif
-    if (promise) {
-      throw new Error('emscripten_asm_const_int_await_promise_on_main_thread is not supported in single-threaded mode');
-    }
 #if ASSERTIONS
     assert(ASM_CONSTS.hasOwnProperty(emAsmAddr), `No EM_ASM constant found at address ${emAsmAddr}.  The loaded WebAssembly file is likely out of sync with the generated JavaScript.`);
 #endif
@@ -1659,7 +1656,14 @@ addToLibrary({
   emscripten_asm_const_int_sync_on_main_thread: (emAsmAddr, sigPtr, argbuf) => runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, 1),
 
   emscripten_asm_const_int_await_promise_on_main_thread__deps: ['$runMainThreadEmAsm'],
-  emscripten_asm_const_int_await_promise_on_main_thread: (emAsmAddr, sigPtr, argbuf) => runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, 1, 1),
+  emscripten_asm_const_int_await_promise_on_main_thread: (emAsmAddr, sigPtr, argbuf) => {
+    #if PTHREADS
+    if (ENVIRONMENT_IS_PTHREAD) {
+      return runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, 1, 1);
+    }
+    #endif
+    throw new Error('call to emscripten_asm_const_int_await_promise_on_main_thread is only supported from pthread (but was called from main thread)');
+  },
 
   emscripten_asm_const_ptr_sync_on_main_thread__deps: ['$runMainThreadEmAsm'],
   emscripten_asm_const_ptr_sync_on_main_thread: (emAsmAddr, sigPtr, argbuf) => runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, 1),

system/include/emscripten/em_asm.h

@@ -254,7 +254,7 @@ const char __em_asm_sig_builder<__em_asm_type_tuple<Args...> >::buffer[] = { __e
 // functions.
 #define MAIN_THREAD_EM_ASM(code, ...) ((void)emscripten_asm_const_int_sync_on_main_thread(CODE_EXPR(#code) _EM_ASM_PREP_ARGS(__VA_ARGS__)))
 
-#define MAIN_THREAD_EM_ASM_PROMISE_AWAIT(code, ...) ((void)emscripten_asm_const_int_await_promise_on_main_thread(CODE_EXPR(#code) _EM_ASM_PREP_ARGS(__VA_ARGS__)))
+#define MAIN_THREAD_EM_ASM_PROMISE_AWAIT(code, ...) emscripten_asm_const_int_await_promise_on_main_thread(CODE_EXPR(#code) _EM_ASM_PREP_ARGS(__VA_ARGS__))
 
 // Runs the given JavaScript code synchronously on the main browser thread, and
 // returns an integer back.

system/lib/pthread/proxying.c

@@ -649,6 +649,9 @@ static void run_js_promise_await(void* arg) {
 }
 
 void _emscripten_proxy_promise_finish(void* res, em_proxying_ctx* ctx) {
+  task* t = (task*)ctx->arg;
+  proxied_js_func_t* func = (proxied_js_func_t*)t->arg;
+  func->result = (double)(intptr_t)res;
   emscripten_proxy_finish(ctx);
 }
 

test/core/test_main_thread_async_em_asm_promise_await.cpp

@@ -9,16 +9,17 @@
 int main()
 {
   printf("Before MAIN_THREAD_EM_ASM_PROMISE_AWAIT\n");
-  MAIN_THREAD_EM_ASM_PROMISE_AWAIT({
+  int res = MAIN_THREAD_EM_ASM_PROMISE_AWAIT({
     out('Inside MAIN_THREAD_EM_ASM_PROMISE_AWAIT: ' + $0 + ' ' + $1);
     const asyncOp = new Promise((resolve,reject) => {
       setTimeout(() => {
         out('Inside asyncOp');
-        resolve();
+        resolve(2);
       }, 1000);
     });
     return asyncOp;
   }, 42, 3.5);
   printf("After MAIN_THREAD_EM_ASM_PROMISE_AWAIT\n");
+  printf("result: %d\n", res);
   return 0;
 }

test/core/test_main_thread_async_em_asm_promise_await.out

@@ -2,3 +2,4 @@ Before MAIN_THREAD_EM_ASM_PROMISE_AWAIT
 Inside MAIN_THREAD_EM_ASM_PROMISE_AWAIT: 42 3.5
 Inside asyncOp
 After MAIN_THREAD_EM_ASM_PROMISE_AWAIT
+result: 2

test/test_core.py

@@ -1905,7 +1905,7 @@ def test_main_thread_async_em_asm_promise_await(self, args, force_c=False):
     if '-sPROXY_TO_PTHREAD' not in args:
       # expect runtime to error
       output = self.do_runf('core/test_main_thread_async_em_asm_promise_await.cpp', expected_output=None, assert_returncode=NON_ZERO, emcc_args=args)
-      self.assertContained('is not supported in single-threaded mode', output)
+      self.assertContained('call to emscripten_asm_const_int_await_promise_on_main_thread is only supported from pthread (but was called from main thread)', output)
     else:
       self.do_core_test('test_main_thread_async_em_asm_promise_await.cpp', emcc_args=args, force_c=force_c)