Proxy known handlers back to the main thread

When running on a pthread, none of the incoming parameters on the
module object are present. Proxy known handlers back to the main
thread if specified.

This simplifies the previous `onAbort` pthread logic for a more
generic solution that also supports the `onExit`, `print` and
`printErr` handlers that can be overridden on the incoming module.

See: #17688.

src/library_pthread.js

@@ -281,12 +281,8 @@ var LibraryPThread = {
           // Worker wants to postMessage() to itself to implement setImmediate()
           // emulation.
           worker.postMessage(d);
-#if expectToReceiveOnModule('onAbort')
-        } else if (cmd === 'onAbort') {
-          if (Module['onAbort']) {
-            Module['onAbort'](d['arg']);
-          }
-#endif
+        } else if (cmd === 'callHandler') {
+          Module[d['handler']](...d['args']);
         } else if (cmd) {
           // The received message looks like something that should be handled by this message
           // handler, (since there is a e.data.cmd field present), but is not one of the
@@ -327,9 +323,33 @@ var LibraryPThread = {
       assert(wasmModule instanceof WebAssembly.Module, 'WebAssembly Module should have been loaded by now!');
 #endif
 
+      // When running on a pthread, none of the incoming parameters on the module
+      // object are present. Proxy known handlers back to the main thread if specified.
+      var handlers = [];
+      var knownHandlers = [
+#if expectToReceiveOnModule('onExit')
+        'onExit',
+#endif
+#if expectToReceiveOnModule('onAbort')
+        'onAbort',
+#endif
+#if expectToReceiveOnModule('print')
+        'print',
+#endif
+#if expectToReceiveOnModule('printErr')
+        'printErr',
+#endif
+      ];
+      for (var handler of knownHandlers) {
+        if (Module.hasOwnProperty(handler)) {
+          handlers.push(handler);
+        }
+      }
+
       // Ask the new worker to load up the Emscripten-compiled page. This is a heavy operation.
       worker.postMessage({
         'cmd': 'load',
+        'handlers': handlers,
         // If the application main .js file was loaded from a Blob, then it is not possible
         // to access the URL of the current script that could be passed to a Web Worker so that
         // it could load up the same file. In that case, developer must either deliver the Blob

src/preamble.js

@@ -455,20 +455,8 @@ function removeRunDependency(id) {
 /** @param {string|number=} what */
 function abort(what) {
 #if expectToReceiveOnModule('onAbort')
-#if USE_PTHREADS
-  // When running on a pthread, none of the incoming parameters on the module
-  // object are present.  The `onAbort` handler only exists on the main thread
-  // and so we need to proxy the handling of these back to the main thread.
-  // TODO(sbc): Extend this to all such handlers that can be passed into on
-  // module creation.
-  if (ENVIRONMENT_IS_PTHREAD) {
-    postMessage({ 'cmd': 'onAbort', 'arg': what});
-  } else
-#endif
-  {
-    if (Module['onAbort']) {
-      Module['onAbort'](what);
-    }
+  if (Module['onAbort']) {
+    Module['onAbort'](what);
   }
 #endif
 

src/worker.js

@@ -136,6 +136,14 @@ self.onmessage = (e) => {
       Module['dynamicLibraries'] = e.data.dynamicLibraries;
 #endif
 
+      // Use `const` here to ensure that the variable is scoped only to
+      // that iteration, allowing safe reference from a closure.
+      for (const handler of e.data.handlers) {
+        Module[handler] = function() {
+          postMessage({ cmd: 'callHandler', handler, args: [...arguments] });
+        }
+      }
+
       {{{ makeAsmImportsAccessInPthread('wasmMemory') }}} = e.data.wasmMemory;
 
 #if LOAD_SOURCE_MAP

test/test_other.py

@@ -12038,6 +12038,28 @@ def test_wasmfs_jsfile_proxying_backend(self):
     self.set_setting('EXIT_RUNTIME')
     self.test_wasmfs_jsfile()
 
+  @node_pthreads
+  def test_wasmfs_print_override_pthread(self):
+    create_file('main.js', '''
+      const Test = require('./test.js');
+
+      async function main() {
+        await Test({
+          // world -> earth
+          print: (text) => console.log(text.replace('world', 'earth'))
+        });
+      }
+      main();
+    ''')
+
+    self.emcc(test_file('hello_world.c'),
+              ['-O3', '-sMODULARIZE', '-sEXPORT_NAME=Test', '-sWASMFS',
+               '-sEXIT_RUNTIME', '-pthread', '-sPROXY_TO_PTHREAD'],
+              output_filename='test.js')
+    output = self.run_js('main.js')
+    self.assertNotContained('hello, world!', output)
+    self.assertContained('hello, earth!', output)
+
   def test_wasmfs_before_preload(self):
     self.set_setting('WASMFS')
     os.mkdir('js_backend_files')