From e475aa1b68e3d54730a619064be9340236e34d64 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc@chromium.org>
Date: Sat, 13 Jun 2026 14:03:04 -0700
Subject: [PATCH] Add a couple more checks/assertions to pthread startup code.
 NFC

I recently saw an issue in Firefox where the CMD_LOAD message was
never received.  This then caused CMD_RUN to crash which in turn
caused `__emscripten_thread_crashed` to be referenced before
initialization.
---
 src/postamble_minimal.js                                  | 2 +-
 src/runtime_common.js                                     | 2 +-
 src/runtime_pthread.js                                    | 5 ++++-
 test/codesize/test_codesize_minimal_pthreads.json         | 8 ++++----
 .../test_codesize_minimal_pthreads_memgrowth.json         | 8 ++++----
 5 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/postamble_minimal.js b/src/postamble_minimal.js
index bf8b65b7af6ef..132faf1d0b06f 100644
--- a/src/postamble_minimal.js
+++ b/src/postamble_minimal.js
@@ -117,7 +117,7 @@ function run() {
 #endif
 
 function initRuntime(wasmExports) {
-#if ASSERTIONS || SAFE_HEAP || USE_ASAN || MODULARIZE
+#if ASSERTIONS || SAFE_HEAP || USE_ASAN || MODULARIZE || PTHREADS
   runtimeInitialized = true;
 #endif
 
diff --git a/src/runtime_common.js b/src/runtime_common.js
index 23a3915cb14cc..aea1cefcef55d 100644
--- a/src/runtime_common.js
+++ b/src/runtime_common.js
@@ -80,7 +80,7 @@ if (ENVIRONMENT_IS_NODE && {{{ ENVIRONMENT_IS_WORKER_THREAD() }}}) {
 var HEAP_DATA_VIEW;
 #endif
 
-#if !MINIMAL_RUNTIME || ASSERTIONS || SAFE_HEAP || USE_ASAN || MODULARIZE
+#if !MINIMAL_RUNTIME || ASSERTIONS || SAFE_HEAP || USE_ASAN || MODULARIZE || PTHREADS
 var runtimeInitialized = false;
 #endif
 
diff --git a/src/runtime_pthread.js b/src/runtime_pthread.js
index 9423a22822487..69023d15a3408 100644
--- a/src/runtime_pthread.js
+++ b/src/runtime_pthread.js
@@ -131,6 +131,9 @@ if (ENVIRONMENT_IS_PTHREAD) {
       } else if (cmd == {{{ CMD_RUN }}}) {
 #if ASSERTIONS
         assert(msgData.pthread_ptr);
+#if !WASM_ESM_INTEGRATION
+        assert(wasmMemory, "CMD_RUN received before CMD_LOAD");
+#endif
 #endif
         // Call inside JS module to set up the stack frame for this pthread in JS module scope.
         // This needs to be the first thing that we do, as we cannot call to any C/C++ functions
@@ -190,7 +193,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
       err(`worker: onmessage() captured an uncaught exception: ${ex}`);
       if (ex?.stack) err(ex.stack);
 #endif
-      __emscripten_thread_crashed();
+      if (runtimeInitialized) __emscripten_thread_crashed();
       throw ex;
     }
   };
diff --git a/test/codesize/test_codesize_minimal_pthreads.json b/test/codesize/test_codesize_minimal_pthreads.json
index a60cc29cf4110..d0c9cb6e314ee 100644
--- a/test/codesize/test_codesize_minimal_pthreads.json
+++ b/test/codesize/test_codesize_minimal_pthreads.json
@@ -1,10 +1,10 @@
 {
-  "a.out.js": 6949,
-  "a.out.js.gz": 3427,
+  "a.out.js": 6969,
+  "a.out.js.gz": 3438,
   "a.out.nodebug.wasm": 19063,
   "a.out.nodebug.wasm.gz": 8803,
-  "total": 26012,
-  "total_gz": 12230,
+  "total": 26032,
+  "total_gz": 12241,
   "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 ad0524a4dd8a1..177e08d93e5b5 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": 7357,
-  "a.out.js.gz": 3627,
+  "a.out.js": 7377,
+  "a.out.js.gz": 3640,
   "a.out.nodebug.wasm": 19064,
   "a.out.nodebug.wasm.gz": 8804,
-  "total": 26421,
-  "total_gz": 12431,
+  "total": 26441,
+  "total_gz": 12444,
   "sent": [
     "a (memory)",
     "b (exit)",