Backup branch

src/jsifier.mjs

@@ -340,7 +340,7 @@ function(${args}) {
             return `
 ${async_}function(${args}) {
 if (ENVIRONMENT_IS_PTHREAD)
-  return ${proxyFunc}(${proxiedFunctionTable.length}, 0, ${+sync}${args ? ', ' : ''}${args});
+  return ${proxyFunc}(${proxiedFunctionTable.length}, 0, ${+sync}, 0${args ? ', ' : ''}${args});
 ${body}
 }\n`;
           });

src/library.js

@@ -1631,7 +1631,7 @@ addToLibrary({
     '$proxyToMainThread'
 #endif
   ],
-  $runMainThreadEmAsm: (emAsmAddr, sigPtr, argbuf, sync) => {
+  $runMainThreadEmAsm: (emAsmAddr, sigPtr, argbuf, sync, asnycAwait) => {
     var args = readEmAsmArgs(sigPtr, argbuf);
 #if PTHREADS
     if (ENVIRONMENT_IS_PTHREAD) {
@@ -1644,7 +1644,7 @@ addToLibrary({
       // of using __proxy. (And dor simplicity, do the same in the sync
       // case as well, even though it's not strictly necessary, to keep the two
       // code paths as similar as possible on both sides.)
-      return proxyToMainThread(0, emAsmAddr, sync, ...args);
+      return proxyToMainThread(0, emAsmAddr, sync, asnycAwait, ...args);
     }
 #endif
 #if ASSERTIONS
@@ -1655,6 +1655,19 @@ addToLibrary({
   emscripten_asm_const_int_sync_on_main_thread__deps: ['$runMainThreadEmAsm'],
   emscripten_asm_const_int_sync_on_main_thread: (emAsmAddr, sigPtr, argbuf) => runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, 1),
 
+  emscripten_asm_const_int_await_on_main_thread__deps: ['$runMainThreadEmAsm'],
+  emscripten_asm_const_int_await_on_main_thread: (emAsmAddr, sigPtr, argbuf) => {
+    #if PTHREADS
+    if (ENVIRONMENT_IS_PTHREAD) {
+      return runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, /*sync=*/1, /*asyncAwait=*/1);
+    }
+    #endif
+    #if ASSERTIONS
+    assert((typeof ENVIRONMENT_IS_PTHREAD !== 'undefined' && ENVIRONMENT_IS_PTHREAD), "emscripten_asm_const_int_await_on_main_thread is not available on the main thread");
+    #endif
+    return runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, /*sync*/1, /*asyncAwait=*/1);
+  },
+
   emscripten_asm_const_ptr_sync_on_main_thread__deps: ['$runMainThreadEmAsm'],
   emscripten_asm_const_ptr_sync_on_main_thread: (emAsmAddr, sigPtr, argbuf) => runMainThreadEmAsm(emAsmAddr, sigPtr, argbuf, 1),
 

src/library_pthread.js

@@ -893,9 +893,9 @@ var LibraryPThread = {
   $proxyToMainThreadPtr: (...args) => BigInt(proxyToMainThread(...args)),
 #endif
 
-  $proxyToMainThread__deps: ['$stackSave', '$stackRestore', '$stackAlloc', '_emscripten_run_on_main_thread_js', ...i53ConversionDeps],
+  $proxyToMainThread__deps: ['$stackSave', '$stackRestore', '$stackAlloc', '_emscripten_run_on_main_thread_js', '_emscripten_await_on_main_thread_js', ...i53ConversionDeps],
   $proxyToMainThread__docs: '/** @type{function(number, (number|boolean), ...number)} */',
-  $proxyToMainThread: (funcIndex, emAsmAddr, sync, ...callArgs) => {
+  $proxyToMainThread: (funcIndex, emAsmAddr, sync, asyncAwait, ...callArgs) => {
     // EM_ASM proxying is done by passing a pointer to the address of the EM_ASM
     // content as `emAsmAddr`.  JS library proxying is done by passing an index
     // into `proxiedJSCallArgs` as `funcIndex`. If `emAsmAddr` is non-zero then
@@ -933,7 +933,12 @@ var LibraryPThread = {
       HEAPF64[b + i] = arg;
 #endif
     }
-    var rtn = __emscripten_run_on_main_thread_js(funcIndex, emAsmAddr, serializedNumCallArgs, args, sync);
+    var rtn;
+    if (asyncAwait) {
+      rtn = __emscripten_await_on_main_thread_js(funcIndex, emAsmAddr, serializedNumCallArgs, args);
+    } else {
+      rtn = __emscripten_run_on_main_thread_js(funcIndex, emAsmAddr, serializedNumCallArgs, args, sync);
+    }
     stackRestore(sp);
     return rtn;
   },
@@ -944,7 +949,7 @@ var LibraryPThread = {
   _emscripten_receive_on_main_thread_js__deps: [
     '$proxyToMainThread',
     '$proxiedJSCallArgs'],
-  _emscripten_receive_on_main_thread_js: (funcIndex, emAsmAddr, callingThread, numCallArgs, args) => {
+  _emscripten_receive_on_main_thread_js: (funcIndex, emAsmAddr, callingThread, numCallArgs, args, promiseCtx) => {
     // Sometimes we need to backproxy events to the calling thread (e.g.
     // HTML5 DOM events handlers such as
     // emscripten_set_mousemove_callback()), so keep track in a globally
@@ -983,6 +988,24 @@ var LibraryPThread = {
     PThread.currentProxiedOperationCallerThread = callingThread;
     var rtn = func(...proxiedJSCallArgs);
     PThread.currentProxiedOperationCallerThread = 0;
+    if (promiseCtx) {
+#if ASSERTIONS
+      assert(!!rtn.then, 'Return value of proxied function expected to be a Promise but got' + rtn);
+#endif
+      rtn.then(res => {
+#if MEMORY64
+    // In memory64 mode some proxied functions return bigint/pointer but
+    // our return type is i53/double.
+    if (typeof res == "bigint") {
+      res = bigintToI53Checked(res);
+    }
+#endif
+      __emscripten_proxy_promise_finish(promiseCtx, res);
+      }).catch(err => {
+        __emscripten_proxy_promise_finish(promiseCtx, err);
+      });
+      return;
+    }
 #if MEMORY64
     // In memory64 mode some proxied functions return bigint/pointer but
     // our return type is i53/double.

src/library_sigs.js

@@ -326,7 +326,7 @@ sigs = {
   _emscripten_notify_mailbox_postmessage__sig: 'vpp',
   _emscripten_push_main_loop_blocker__sig: 'vppp',
   _emscripten_push_uncounted_main_loop_blocker__sig: 'vppp',
-  _emscripten_receive_on_main_thread_js__sig: 'dippip',
+  _emscripten_receive_on_main_thread_js__sig: 'dippipp',
   _emscripten_runtime_keepalive_clear__sig: 'v',
   _emscripten_set_offscreencanvas_size__sig: 'ipii',
   _emscripten_system__sig: 'ip',
@@ -569,6 +569,7 @@ sigs = {
   emscripten_asm_const_double__sig: 'dppp',
   emscripten_asm_const_double_sync_on_main_thread__sig: 'dppp',
   emscripten_asm_const_int__sig: 'ippp',
+  emscripten_asm_const_int_await_on_main_thread__sig: 'ippp',
   emscripten_asm_const_int_sync_on_main_thread__sig: 'ippp',
   emscripten_asm_const_ptr__sig: 'pppp',
   emscripten_asm_const_ptr_sync_on_main_thread__sig: 'pppp',

system/include/emscripten/em_asm.h

@@ -28,6 +28,9 @@ __attribute__((nothrow))
 int emscripten_asm_const_int_sync_on_main_thread(
   const char* code, const char* arg_sigs, ...);
 __attribute__((nothrow))
+int emscripten_asm_const_int_await_on_main_thread(
+  const char* code, const char* arg_sigs, ...);
+__attribute__((nothrow))
 void* emscripten_asm_const_ptr_sync_on_main_thread(
   const char* code, const char* arg_sigs, ...);
 __attribute__((nothrow))
@@ -51,6 +54,7 @@ void emscripten_asm_const_async_on_main_thread(
 #define EM_ASM_PTR(...) EM_ASM_ERROR
 #define EM_ASM_DOUBLE(...) EM_ASM_ERROR
 #define MAIN_THREAD_EM_ASM(...) EM_ASM_ERROR
+#define MAIN_THREAD_EM_ASM_AWAIT(...) EM_ASM_ERROR
 #define MAIN_THREAD_EM_ASM_INT(...) EM_ASM_ERROR
 #define MAIN_THREAD_EM_ASM_PTR(...) EM_ASM_ERROR
 #define MAIN_THREAD_EM_ASM_DOUBLE(...) EM_ASM_ERROR
@@ -250,6 +254,13 @@ 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__)))
 
+// Runs the given Javascript code on the main browser thread.
+// It must be called from a non-main thread.
+// The code must return a promise, and this function will wait for the promise
+// to resolve or reject, essentially blocking the calling thread until then.
+// In either case the function will return an integer, which is the result of the promise.
+#define MAIN_THREAD_EM_ASM_AWAIT(code, ...) emscripten_asm_const_int_await_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.
 // The same considerations apply as with MAIN_THREAD_EM_ASM().

system/lib/pthread/proxying.c

@@ -13,6 +13,7 @@
 #include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdio.h>
 
 #include "em_task_queue.h"
 #include "thread_mailbox.h"
@@ -35,6 +36,20 @@ static em_proxying_queue system_proxying_queue = {
   .capacity = 0,
 };
 
+typedef struct proxied_js_func_t {
+  int funcIndex;
+  void* emAsmAddr;
+  pthread_t callingThread;
+  int numArgs;
+  double* argBuffer;
+  double result;
+  bool owned;
+  // Only used when when the underlying JS function is async and ctx need to be 
+  // resolved on promise end.
+  // should be NULL if the function is sync.
+  em_proxying_ctx * ctx;
+} proxied_js_func_t;
+
 em_proxying_queue* emscripten_proxy_get_system_queue(void) {
   return &system_proxying_queue;
 }
@@ -397,6 +412,14 @@ static void call_then_finish_task(em_proxying_ctx* ctx, void* arg) {
   emscripten_proxy_finish(ctx);
 }
 
+static void call_proxied_js_task_with_ctx(em_proxying_ctx* ctx, void* arg) {
+  // Stash the context on the proxied_js_func_t argument.
+  task* t = arg;
+  proxied_js_func_t* p = t->arg;
+  p->ctx = ctx;
+  t->func(t->arg);
+}
+
 int emscripten_proxy_sync(em_proxying_queue* q,
                           pthread_t target_thread,
                           void (*func)(void*),
@@ -583,20 +606,10 @@ em_promise_t emscripten_proxy_promise(em_proxying_queue* q,
                           &block->promise_ctx);
 }
 
-typedef struct proxied_js_func_t {
-  int funcIndex;
-  void* emAsmAddr;
-  pthread_t callingThread;
-  int numArgs;
-  double* argBuffer;
-  double result;
-  bool owned;
-} proxied_js_func_t;
-
 static void run_js_func(void* arg) {
   proxied_js_func_t* f = (proxied_js_func_t*)arg;
   f->result = _emscripten_receive_on_main_thread_js(
-    f->funcIndex, f->emAsmAddr, f->callingThread, f->numArgs, f->argBuffer);
+    f->funcIndex, f->emAsmAddr, f->callingThread, f->numArgs, f->argBuffer, f->ctx);
   if (f->owned) {
     free(f->argBuffer);
     free(f);
@@ -615,6 +628,7 @@ double _emscripten_run_on_main_thread_js(int func_index,
     .numArgs = num_args,
     .argBuffer = buffer,
     .owned = false,
+    .ctx = NULL,
   };
 
   em_proxying_queue* q = emscripten_proxy_get_system_queue();
@@ -642,3 +656,34 @@ double _emscripten_run_on_main_thread_js(int func_index,
   }
   return 0;
 }
+
+double _emscripten_await_on_main_thread_js(int func_index,
+                                           void* em_asm_addr,
+                                           int num_args,
+                                           double* buffer) {
+  em_proxying_queue* q = emscripten_proxy_get_system_queue();
+  pthread_t target = emscripten_main_runtime_thread_id();
+
+  proxied_js_func_t f = {
+    .funcIndex = func_index,
+    .emAsmAddr = em_asm_addr,
+    .callingThread = pthread_self(),
+    .numArgs = num_args,
+    .argBuffer = buffer,
+    .owned = false,
+  };
+  task t = {.func = run_js_func, .arg = &f};
+
+  if (!emscripten_proxy_sync_with_ctx(q, target, call_proxied_js_task_with_ctx, &t)) {
+    assert(false && "emscripten_proxy_sync_with_ctx failed");
+    return 0;
+  }
+  return f.result;
+}
+
+void _emscripten_proxy_promise_finish(em_proxying_ctx* ctx, void* res) {
+  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);
+}

system/lib/pthread/threading_internal.h

@@ -96,7 +96,7 @@ int __pthread_create_js(struct __pthread *thread, const pthread_attr_t *attr, vo
 int _emscripten_default_pthread_stack_size();
 void __set_thread_state(pthread_t ptr, int is_main, int is_runtime, int can_block);
 
-double _emscripten_receive_on_main_thread_js(int funcIndex, void* emAsmAddr, pthread_t callingThread, int numCallArgs, double* args);
+double _emscripten_receive_on_main_thread_js(int funcIndex, void* emAsmAddr, pthread_t callingThread, int numCallArgs, double* args, void *ctx);
 
 // Return non-zero if the calling thread supports Atomic.wait (For example
 // if called from the main browser thread, this function will return zero

test/core/test_main_thread_async_em_asm_await.cpp

@@ -0,0 +1,25 @@
+// Copyright 2024 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <emscripten.h>
+#include <stdio.h>
+
+int main()
+{
+  printf("Before MAIN_THREAD_EM_ASM_AWAIT\n");
+  int res = MAIN_THREAD_EM_ASM_AWAIT({
+    out('Inside MAIN_THREAD_EM_ASM_AWAIT: ' + $0 + ' ' + $1);
+    const asyncOp = new Promise((resolve,reject) => {
+      setTimeout(() => {
+        out('Inside asyncOp');
+        resolve(2);
+      }, 1000);
+    });
+    return asyncOp;
+  }, 42, 3.5);
+  printf("After MAIN_THREAD_EM_ASM_AWAIT\n");
+  printf("result: %d\n", res);
+  return 0;
+}

test/core/test_main_thread_async_em_asm_await.out

@@ -0,0 +1,5 @@
+Before MAIN_THREAD_EM_ASM_AWAIT
+Inside MAIN_THREAD_EM_ASM_AWAIT: 42 3.5
+Inside asyncOp
+After MAIN_THREAD_EM_ASM_AWAIT
+result: 2

test/core/test_main_thread_async_em_asm_await_reject.cpp

@@ -0,0 +1,34 @@
+// Copyright 2024 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <emscripten.h>
+#include <stdio.h>
+#include <pthread.h>
+
+int main()
+{
+  // start new thread
+  pthread_t thread;
+  pthread_create(&thread, NULL, [](void*) -> void* {
+    printf("Before MAIN_THREAD_EM_ASM_AWAIT\n");
+    int res = MAIN_THREAD_EM_ASM_AWAIT({
+      out('Inside MAIN_THREAD_EM_ASM_AWAIT: ' + $0 + ' ' + $1);
+      const asyncOp = new Promise((resolve,reject) => {
+        setTimeout(() => {
+          out('Inside asyncOp');
+          reject(2);
+        }, 1000);
+      });
+      return asyncOp;
+    }, 42, 3.5);
+    printf("After MAIN_THREAD_EM_ASM_AWAIT rejected\n");
+    printf("result: %d\n", res);
+    return NULL;
+  }, NULL);
+
+  // wait for thread to finish
+  pthread_join(thread, NULL);
+  return 0;
+}

test/core/test_main_thread_async_em_asm_await_reject.out

@@ -0,0 +1,5 @@
+Before MAIN_THREAD_EM_ASM_AWAIT
+Inside MAIN_THREAD_EM_ASM_AWAIT: 42 3.5
+Inside asyncOp
+After MAIN_THREAD_EM_ASM_AWAIT rejected
+result: 2

test/other/codesize/test_codesize_minimal_pthreads.size

@@ -1 +1 @@
-19487
+19495

test/other/test_unoptimized_code_size.js.size

@@ -1 +1 @@
-53709
+53980

test/other/test_unoptimized_code_size_no_asserts.js.size

@@ -1 +1 @@
-29018
+29400

test/other/test_unoptimized_code_size_strict.js.size

@@ -1 +1 @@
-52531
+52776

test/test_core.py

@@ -1878,6 +1878,26 @@ def test_main_thread_em_asm(self, args):
   def test_main_thread_async_em_asm(self, args, force_c=False):
     self.do_core_test('test_main_thread_async_em_asm.cpp', emcc_args=args, force_c=force_c)
 
+  @needs_dylink
+  @parameterized({
+    '': (['-sASSERTIONS'], False),
+    'pthreads': (['-pthread', '-sPROXY_TO_PTHREAD', '-sEXIT_RUNTIME'], False),
+  })
+  def test_main_thread_async_em_asm_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_await.cpp', expected_output=None, assert_returncode=NON_ZERO, emcc_args=args)
+      self.assertContained('emscripten_asm_const_int_await_on_main_thread is not available on the main thread', output)
+    else:
+      self.do_core_test('test_main_thread_async_em_asm_await.cpp', emcc_args=args, force_c=force_c)
+
+  @needs_dylink
+  @parameterized({
+    'pthreads': (['-pthread', '-sPROXY_TO_PTHREAD', '-sEXIT_RUNTIME', '-sASSERTIONS'], False),
+  })
+  def test_main_thread_async_em_asm_await_reject(self, args, force_c=False):
+    self.do_core_test('test_main_thread_async_em_asm_await_reject.cpp', emcc_args=args, force_c=force_c)
+
   # Tests MAIN_THREAD_EM_ASM_INT() function call with different signatures.
   def test_main_thread_em_asm_signatures(self):
     self.do_core_test('test_em_asm_signatures.cpp', assert_returncode=NON_ZERO)

tools/emscripten.py

@@ -1074,6 +1074,8 @@ def create_pointer_conversion_wrappers(metadata):
     '_wasmfs_read_file': 'pp',
     '__dl_seterr': '_pp',
     '_emscripten_run_on_main_thread_js': '__p_p_',
+    '_emscripten_await_on_main_thread_js': '__p_p_',
+    '_emscripten_proxy_promise_finish': 'pp',
     '_emscripten_proxy_execute_task_queue': '_p',
     '_emscripten_thread_exit': '_p',
     '_emscripten_thread_init': '_p_____',