Sequentialize uncaught exceptions in Node.js Workers (#25041)

Sequentialize uncaught exceptions in Node.js Workers into the same
postMessage() stream that other messages go through, to ensure they are
received by the main thread in the order they were generated.

Fixes #15014.

See nodejs/node#59617.

Author: juj

src/lib/libpthread.js

@@ -241,6 +241,9 @@ var LibraryPThread = {
       worker.onmessage = (e) => {
         var d = e['data'];
         var cmd = d.cmd;
+#if PTHREADS_DEBUG
+        dbg(`main thread: received message '${cmd}' from worker. ${d}`);
+#endif
 
         // If this message is intended to a recipient that is not the main
         // thread, forward it to the target thread.
@@ -283,6 +286,13 @@ var LibraryPThread = {
           // Worker wants to postMessage() to itself to implement setImmediate()
           // emulation.
           worker.postMessage(d);
+#if ENVIRONMENT_MAY_BE_NODE
+        } else if (cmd === 'uncaughtException') {
+          // Message handler for Node.js specific out-of-order behavior:
+          // https://github.com/nodejs/node/issues/59617
+          // A pthread sent an uncaught exception event. Re-raise it on the main thread.
+          worker.onerror(d.error);
+#endif
         } else if (cmd === 'callHandler') {
           Module[d.handler](...d.args);
         } else if (cmd) {
@@ -308,6 +318,13 @@ var LibraryPThread = {
       if (ENVIRONMENT_IS_NODE) {
         worker.on('message', (data) => worker.onmessage({ data: data }));
         worker.on('error', (e) => worker.onerror(e));
+
+#if PTHREADS_DEBUG
+        worker.on('exit', (code) => {
+          if (worker.pthread_ptr) dbg(`Worker hosting pthread ${ptrToString(worker.pthread_ptr)} has terminated with code ${code}.`);
+          else dbg(`Worker has terminated with code ${code}.`);
+        });
+#endif
       }
 #endif
 

src/runtime_common.js

@@ -40,6 +40,21 @@ if (ENVIRONMENT_IS_NODE && {{{ ENVIRONMENT_IS_WORKER_THREAD() }}}) {
     self: global,
     postMessage: (msg) => parentPort['postMessage'](msg),
   });
+  // Node.js Workers do not pass postMessage()s and uncaught exception events to the parent
+  // thread necessarily in the same order where they were generated in sequential program order.
+  // See https://github.com/nodejs/node/issues/59617
+  // To remedy this, capture all uncaughtExceptions in the Worker, and sequentialize those over
+  // to the same postMessage pipe that other messages use.
+  process.on("uncaughtException", (err) => {
+#if PTHREADS_DEBUG
+    dbg(`uncaughtException on worker thread: ${err.message}`);
+#endif
+    postMessage({ cmd: 'uncaughtException', error: err });
+    // Also shut down the Worker to match the same semantics as if this uncaughtException
+    // handler was not registered.
+    // (n.b. this will not shut down the whole Node.js app process, but just the Worker)
+    process.exit(1);
+  });
 }
 #endif // (PTHREADS || WASM_WORKERS) && (ENVIRONMENT_MAY_BE_NODE && !WASM_ESM_INTEGRATION)
 

test/code_size/test_codesize_minimal_pthreads.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 7499,
-  "a.out.js.gz": 3721,
+  "a.out.js": 7649,
+  "a.out.js.gz": 3768,
   "a.out.nodebug.wasm": 19588,
   "a.out.nodebug.wasm.gz": 9025,
-  "total": 27087,
-  "total_gz": 12746,
+  "total": 27237,
+  "total_gz": 12793,
   "sent": [
     "a (memory)",
     "b (emscripten_get_now)",

test/code_size/test_codesize_minimal_pthreads_memgrowth.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 7926,
-  "a.out.js.gz": 3924,
+  "a.out.js": 8076,
+  "a.out.js.gz": 3974,
   "a.out.nodebug.wasm": 19589,
   "a.out.nodebug.wasm.gz": 9025,
-  "total": 27515,
-  "total_gz": 12949,
+  "total": 27665,
+  "total_gz": 12999,
   "sent": [
     "a (memory)",
     "b (emscripten_get_now)",

test/test_core.py

@@ -24,7 +24,7 @@
 from tools import shared, building, config, utils, webassembly
 import common
 from common import RunnerCore, path_from_root, requires_native_clang, test_file, create_file
-from common import skip_if, no_windows, no_mac, is_slow_test, parameterized, parameterize
+from common import skip_if, no_windows, is_slow_test, parameterized, parameterize
 from common import env_modify, with_env_modify, disabled, flaky, node_pthreads, also_without_bigint
 from common import read_file, read_binary, requires_v8, requires_node, requires_dev_dependency, requires_wasm2js, requires_node_canary
 from common import compiler_for, crossplatform, no_4gb, no_2gb, also_with_minimal_runtime, also_with_modularize
@@ -2669,8 +2669,6 @@ def test_pthread_attr_getstack(self):
     self.do_run_in_out_file_test('pthread/test_pthread_attr_getstack.c')
 
   @node_pthreads
-  @no_mac('https://github.com/emscripten-core/emscripten/issues/15014')
-  @flaky('https://github.com/emscripten-core/emscripten/issues/15014')
   def test_pthread_abort(self):
     self.set_setting('PROXY_TO_PTHREAD')
     # Add the onAbort handler at runtime during preRun.  This means that onAbort