remove the need for manual cleanup in async ccalls #3307

site/source/docs/api_reference/preamble.js.rst

@@ -58,7 +58,7 @@ Calling compiled C functions from JavaScript
 	:returns: The result of the function call as a native JavaScript value (as in ``returnType``).
 	:opts: An optional options object. It can contain the following properties:
 
-			- ``async``: Implies that the ccall will perform an async operation. This assumes you are using the Emterpreter-Async option for your code. When using this option, the ccalled function cannot return a value (it can't be received synchronously anyhow); instead, ccall will return a function that you should call after all asynchronous operations conclude (the function does some cleanup).
+			- ``async``: Implies that the ccall will perform an async operation. This assumes you are using the Emterpreter-Async option for your code. When using this option, the ccalled function cannot return a value (it can't be received synchronously anyhow).
 
 	.. COMMENT (not rendered): The ccall/cwrap functions only work for C++ functions that use "extern C". In theory ordinary C++ names can be unmangled, but it would require tool to ship a fairly large amount of code just for this purpose.
 

src/library_async.js

@@ -214,6 +214,7 @@ mergeInto(LibraryManager.library, {
     saveStack: '',
     yieldCallbacks: [],
     postAsync: null,
+    asyncFinalizers: [], // functions to run when all asynchronicity is done
 
     ensureInit: function() {
       if (this.initted) return;
@@ -275,6 +276,12 @@ mergeInto(LibraryManager.library, {
             // if we did *not* do another async operation, then we know that nothing is conceptually on the stack now, and we can re-allow async callbacks as well as run the queued ones right now
             Browser.resumeAsyncCallbacks();
           }
+          if (EmterpreterAsync.state === 0) {
+            EmterpreterAsync.asyncFinalizers.forEach(function(func) {
+              func();
+            });
+            EmterpreterAsync.asyncFinalizers.length = 0;
+          }
         });
         EmterpreterAsync.setState(1);
 #if ASSERTIONS

src/preamble.js

@@ -393,9 +393,10 @@ var cwrap, ccall;
     if (returnType === 'string') ret = Pointer_stringify(ret);
     if (stack !== 0) {
       if (opts && opts.async) {
-        return function() {
+        EmterpreterAsync.asyncFinalizers.push(function() {
           Runtime.stackRestore(stack);
-        };
+        });
+        return;
       }
       Runtime.stackRestore(stack);
     }

tests/test_core.py

@@ -7378,17 +7378,12 @@ int main() {
   printf("Hello");
   emscripten_sleep(100);
   printf("World\n");
-  EM_ASM( Module.doCleanup() );
 }
 '''
       open('post.js', 'w').write('''
-Module.cleanup = Module['ccall']('main', null, ['number', 'string'], [2, 'waka'], { async: true });
+Module['ccall']('main', null, ['number', 'string'], [2, 'waka'], { async: true });
-Module.doCleanup = function() {
-  Module.print('cleanup');
-  Module.cleanup();
-};
 ''')
-      self.do_run(src, 'HelloWorld\ncleanup');
+      self.do_run(src, 'HelloWorld');
 
   def test_coroutine(self):
     if not Settings.ASM_JS: return self.skip('asyncify requires asm.js')