From cc426e2e80f31497c817be6665aac2e1284cca22 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Thu, 20 Aug 2026 16:38:27 -0700
Subject: [PATCH] Fix Bun 1.4 + pthreads by always bridging `parentPort` in
 worker threads

In #25947, a check for `!globalThis.postMessage` was added before
wiring `parentPort.on('message') -> globalThis.onmessage` and
`globalThis.postMessage = (msg) => parentPort.postMessage(msg)`.

However, in Bun 1.4+, `node:worker_threads` deliveries are isolated to
`parentPort` (they are no longer automatically routed to
`globalThis.onmessage`), while `globalThis.postMessage` remains defined
on the global object. Because `globalThis.postMessage` was truthy,
Emscripten skipped hooking `parentPort.on('message')`, leaving worker
threads unresponsive to initialization messages from the main thread.

Removing the `if (!globalThis.postMessage)` guard ensures `parentPort`
is always correctly wired whenever running in a Node-style worker
thread.

Fixes: #27580
---
 .circleci/config.yml                                     | 5 +----
 src/pthread_esm_startup.mjs                              | 9 ++-------
 src/runtime_common.js                                    | 9 ++-------
 test/codesize/test_codesize_minimal_pthreads.json        | 8 ++++----
 .../test_codesize_minimal_pthreads_memgrowth.json        | 8 ++++----
 5 files changed, 13 insertions(+), 26 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index bfb12cd2ed94e..2c4d7219d47fc 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -805,10 +805,7 @@ jobs:
       - run:
           name: install bun
           command: |
-            # Temporally pin to 1.3.14 (the last non-rust version) until we
-            # can investigate the breakages:
-            # https://github.com/emscripten-core/emscripten/issues/27580
-            curl -fsSL https://bun.com/install | bash -s "bun-v1.3.14"
+            curl -fsSL https://bun.com/install | bash
             echo "BUN = '~/.bun/bin/bun'" >> ~/emsdk/.emscripten
             echo "JS_ENGINES = [BUN]" >> ~/emsdk/.emscripten
       - run-tests:
diff --git a/src/pthread_esm_startup.mjs b/src/pthread_esm_startup.mjs
index 6054fb99b9237..7a5f534022dd5 100644
--- a/src/pthread_esm_startup.mjs
+++ b/src/pthread_esm_startup.mjs
@@ -20,13 +20,8 @@ if ({{{ nodeDetectionCode() }}}) {
   var worker_threads = await import('node:worker_threads');
   globalThis.Worker = worker_threads.Worker;
   var parentPort = worker_threads.parentPort;
-  // Deno and Bun already have `postMessage` defined on the global scope and
-  // deliver messages to `globalThis.onmessage`, so we must not duplicate that
-  // behavior here if `postMessage` is already present.
-  if (!globalThis.postMessage) {
-    parentPort.on('message', (msg) => globalThis.onmessage?.({ data: msg }));
-    globalThis.postMessage = (msg) => parentPort.postMessage(msg);
-  }
+  parentPort.on('message', (msg) => globalThis.onmessage?.({ data: msg }));
+  globalThis.postMessage = (msg) => parentPort.postMessage(msg);
 }
 #endif
 
diff --git a/src/runtime_common.js b/src/runtime_common.js
index 09bf17956aa6d..379d12ac4690f 100644
--- a/src/runtime_common.js
+++ b/src/runtime_common.js
@@ -39,13 +39,8 @@ if (ENVIRONMENT_IS_NODE && {{{ ENVIRONMENT_IS_WORKER_THREAD() }}}) {
   // Create as web-worker-like an environment as we can.
   globalThis.self = globalThis;
   var parentPort = worker_threads.parentPort;
-  // Deno and Bun already have `postMessage` defined on the global scope and
-  // deliver messages to `globalThis.onmessage`, so we must not duplicate that
-  // behavior here if `postMessage` is already present.
-  if (!globalThis.postMessage) {
-    parentPort.on('message', (msg) => globalThis.onmessage?.({ data: msg }));
-    globalThis.postMessage = (msg) => parentPort.postMessage(msg);
-  }
+  parentPort.on('message', (msg) => globalThis.onmessage?.({ data: msg }));
+  globalThis.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
diff --git a/test/codesize/test_codesize_minimal_pthreads.json b/test/codesize/test_codesize_minimal_pthreads.json
index d0651f8052264..0e32d28d17872 100644
--- a/test/codesize/test_codesize_minimal_pthreads.json
+++ b/test/codesize/test_codesize_minimal_pthreads.json
@@ -1,10 +1,10 @@
 {
-  "a.out.js": 6883,
-  "a.out.js.gz": 3422,
+  "a.out.js": 6857,
+  "a.out.js.gz": 3416,
   "a.out.nodebug.wasm": 19132,
   "a.out.nodebug.wasm.gz": 8845,
-  "total": 26015,
-  "total_gz": 12267,
+  "total": 25989,
+  "total_gz": 12261,
   "sent": [
     "a (memory)",
     "b (exit)",
diff --git a/test/codesize/test_codesize_minimal_pthreads_memgrowth.json b/test/codesize/test_codesize_minimal_pthreads_memgrowth.json
index c258456676ca6..822216dfa330e 100644
--- a/test/codesize/test_codesize_minimal_pthreads_memgrowth.json
+++ b/test/codesize/test_codesize_minimal_pthreads_memgrowth.json
@@ -1,10 +1,10 @@
 {
-  "a.out.js": 7341,
-  "a.out.js.gz": 3639,
+  "a.out.js": 7315,
+  "a.out.js.gz": 3633,
   "a.out.nodebug.wasm": 19133,
   "a.out.nodebug.wasm.gz": 8846,
-  "total": 26474,
-  "total_gz": 12485,
+  "total": 26448,
+  "total_gz": 12479,
   "sent": [
     "a (memory)",
     "b (exit)",