Prevent idle Workers from keeping Node.js app alive

src/closure-externs/node-externs.js

@@ -111,3 +111,6 @@ Buffer.prototype.slice = function(start, end) {};
  * @nosideeffects
  */
 Buffer.prototype.toString = function(encoding, start, end) {};
+
+Worker.prototype.ref = function() {};
+Worker.prototype.unref = function() {};

src/library_pthread.js

@@ -205,6 +205,15 @@ var LibraryPThread = {
       // worker pool as an unused worker.
       worker.pthread_ptr = 0;
 
+#if ENVIRONMENT_MAY_BE_NODE
+      if (ENVIRONMENT_IS_NODE) {
+        // Once a pthread has finished and the worker becomes idle, mark it
+        // as weakly referenced so that its existence does not prevent Node.js
+        // from exiting.
+        worker.unref();
+      }
+#endif
+
       // Finally, free the underlying (and now-unused) pthread structure in
       // linear memory.
       __emscripten_thread_free_data(pthread_ptr);
@@ -267,11 +276,18 @@ var LibraryPThread = {
           cancelThread(d['thread']);
         } else if (cmd === 'loaded') {
           worker.loaded = true;
+#if ENVIRONMENT_MAY_BE_NODE
+          if (ENVIRONMENT_IS_NODE) {
+            // Once worker is loaded & idle, mark it as weakly referenced,
+            // so that mere existence of a Worker in the pool does not prevent
+            // Node.js from exiting the app.
+            worker.unref();
+          }
+#endif
           if (onFinishedLoading) onFinishedLoading(worker);
           // If this Worker is already pending to start running a thread, launch the thread now
           if (worker.runPthread) {
             worker.runPthread();
-            delete worker.runPthread;
           }
         } else if (cmd === 'print') {
           out('Thread ' + d['threadId'] + ': ' + d['text']);
@@ -584,12 +600,19 @@ var LibraryPThread = {
 #endif
     worker.runPthread = () => {
       // Ask the worker to start executing its pthread entry point function.
+#if ENVIRONMENT_MAY_BE_NODE
+      if (ENVIRONMENT_IS_NODE) {
+        // Mark worker as strongly referenced once we start executing a pthread,
+        // so that Node.js doesn't exit while the pthread is running.
+        worker.ref();
+      }
+#endif
       msg.time = performance.now();
       worker.postMessage(msg, threadParams.transferList);
+      delete worker.runPthread;
     };
     if (worker.loaded) {
       worker.runPthread();
-      delete worker.runPthread;
     }
     return 0;
   },
@@ -671,7 +694,7 @@ var LibraryPThread = {
 
     var offscreenCanvases = {}; // Dictionary of OffscreenCanvas objects we'll transfer to the created thread to own
     var moduleCanvasId = Module['canvas'] ? Module['canvas'].id : '';
-    // Note that transferredCanvasNames might be null (so we cannot do a for-of loop).  
+    // Note that transferredCanvasNames might be null (so we cannot do a for-of loop).
     for (var i in transferredCanvasNames) {
       var name = transferredCanvasNames[i].trim();
       var offscreenCanvasInfo;

test/test_core.py

@@ -2766,7 +2766,6 @@ def test_pthread_proxying_cpp(self):
 
   @node_pthreads
   def test_pthread_proxying_dropped_work(self):
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('PTHREAD_POOL_SIZE=2')
     self.do_run_in_out_file_test('pthread/test_pthread_proxying_dropped_work.c')
 
@@ -2779,7 +2778,6 @@ def test_pthread_proxying_refcount(self):
 
   @node_pthreads
   def test_pthread_dispatch_after_exit(self):
-    self.set_setting('EXIT_RUNTIME')
     self.do_run_in_out_file_test('pthread/test_pthread_dispatch_after_exit.c', interleaved_output=False)
 
   @node_pthreads
@@ -2791,7 +2789,6 @@ def test_pthread_atexit(self):
 
   @node_pthreads
   def test_pthread_nested_work_queue(self):
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('PTHREAD_POOL_SIZE', 1)
     self.do_run_in_out_file_test('pthread/test_pthread_nested_work_queue.c')
 
@@ -2804,13 +2801,11 @@ def test_pthread_thread_local_storage(self):
 
   @node_pthreads
   def test_pthread_cleanup(self):
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('PTHREAD_POOL_SIZE', 4)
     self.do_run_in_out_file_test('pthread/test_pthread_cleanup.cpp')
 
   @node_pthreads
   def test_pthread_setspecific_mainthread(self):
-    self.set_setting('EXIT_RUNTIME')
     print('.. return')
     self.do_runf(test_file('pthread/test_pthread_setspecific_mainthread.c'), 'done!', emcc_args=['-DRETURN'])
     print('.. exit')
@@ -2820,7 +2815,6 @@ def test_pthread_setspecific_mainthread(self):
 
   @node_pthreads
   def test_pthread_attr_getstack(self):
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('PTHREAD_POOL_SIZE', 1)
     self.do_run_in_out_file_test('pthread/test_pthread_attr_getstack.c')
 
@@ -2836,7 +2830,6 @@ def test_pthread_abort(self):
 
   @node_pthreads
   def test_pthread_abort_interrupt(self):
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('PTHREAD_POOL_SIZE', 1)
     expected = ['Aborted(). Build with -sASSERTIONS for more info', 'Aborted(native code called abort())']
     self.do_runf(test_file('pthread/test_pthread_abort_interrupt.c'), expected, assert_returncode=NON_ZERO)
@@ -9112,13 +9105,11 @@ def test_pthread_c11_threads(self):
   @node_pthreads
   def test_pthread_cxx_threads(self):
     self.set_setting('PTHREAD_POOL_SIZE', 1)
-    self.set_setting('EXIT_RUNTIME')
     self.do_run_in_out_file_test('pthread/test_pthread_cxx_threads.cpp')
 
   @node_pthreads
   def test_pthread_busy_wait(self):
     self.set_setting('PTHREAD_POOL_SIZE', 1)
-    self.set_setting('EXIT_RUNTIME')
     self.do_run_in_out_file_test('pthread/test_pthread_busy_wait.cpp')
 
   @node_pthreads
@@ -9167,11 +9158,9 @@ def test_pthread_exit_process(self):
 
   @node_pthreads
   def test_pthread_exit_main(self):
-    self.set_setting('EXIT_RUNTIME')
     self.do_run_in_out_file_test('core/pthread/test_pthread_exit_main.c')
 
   def test_pthread_exit_main_stub(self):
-    self.set_setting('EXIT_RUNTIME')
     self.do_run_in_out_file_test('core/pthread/test_pthread_exit_main.c')
 
   @node_pthreads
@@ -9223,7 +9212,6 @@ def test_emscripten_futexes(self):
   @node_pthreads
   def test_stdio_locking(self):
     self.set_setting('PTHREAD_POOL_SIZE', '2')
-    self.set_setting('EXIT_RUNTIME')
     self.do_run_in_out_file_test('core/test_stdio_locking.c')
 
   @needs_dylink
@@ -9238,7 +9226,6 @@ def test_pthread_dylink_basics(self):
   @node_pthreads
   def test_pthread_dylink(self):
     self.emcc_args.append('-Wno-experimental')
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('USE_PTHREADS')
     self.set_setting('PTHREAD_POOL_SIZE', 2)
     main = test_file('core/pthread/test_pthread_dylink.c')
@@ -9259,7 +9246,6 @@ def test_pthread_dylink(self):
   @node_pthreads
   def test_pthread_dylink_entry_point(self, args):
     self.emcc_args.append('-Wno-experimental')
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('USE_PTHREADS')
     self.set_setting('PTHREAD_POOL_SIZE', 1)
     main = test_file('core/pthread/test_pthread_dylink_entry_point.c')
@@ -9269,7 +9255,6 @@ def test_pthread_dylink_entry_point(self, args):
   @node_pthreads
   def test_pthread_dylink_exceptions(self):
     self.emcc_args.append('-Wno-experimental')
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('USE_PTHREADS')
     self.emcc_args.append('-fexceptions')
     self.dylink_testf(test_file('core/pthread/test_pthread_dylink_exceptions.cpp'))
@@ -9312,7 +9297,6 @@ def test_pthread_dlsym(self):
   @node_pthreads
   def test_pthread_dylink_tls(self):
     self.emcc_args.append('-Wno-experimental')
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('USE_PTHREADS')
     self.set_setting('PTHREAD_POOL_SIZE', 1)
     main = test_file('core/pthread/test_pthread_dylink_tls.c')
@@ -9322,7 +9306,6 @@ def test_pthread_dylink_tls(self):
   @node_pthreads
   def test_pthread_dylink_longjmp(self):
     self.emcc_args.append('-Wno-experimental')
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('USE_PTHREADS')
     self.set_setting('PTHREAD_POOL_SIZE=1')
     main = test_file('core/pthread/test_pthread_dylink_longjmp.c')
@@ -9332,7 +9315,6 @@ def test_pthread_dylink_longjmp(self):
   @node_pthreads
   def test_pthread_dylink_main_module_1(self):
     self.emcc_args.append('-Wno-experimental')
-    self.set_setting('EXIT_RUNTIME')
     self.set_setting('USE_PTHREADS')
     self.set_setting('MAIN_MODULE')
     self.do_runf(test_file('hello_world.c'))

test/test_other.py

@@ -9101,7 +9101,6 @@ def test_node_js_pthread_module(self):
 const test_module = require("./module");
 test_module().then((test_module_instance) => {
   test_module_instance._main();
-  process.exit(0);
 });
 '''
     ensure_dir('subdir')