From 68741e3629966b668901e309aca6307d09d1e1f7 Mon Sep 17 00:00:00 2001
From: Nate Bracy <nate@bracy.dev>
Date: Wed, 16 Sep 2026 23:33:25 -0400
Subject: [PATCH 1/3] Exit proxied main with its status when keepalives run out

With -pthread -sPROXY_TO_PTHREAD -sEXIT_RUNTIME, a main() that returns while a runtime keepalive is held now exits with its status once the count reaches zero, instead of exiting 0 with atexit handlers skipped.

Fixes #27721
---
 src/lib/libcore.js                            | 20 ++++++++
 src/lib/libpthread.js                         | 23 +++++++++
 system/lib/libc/crt1_proxy_main.c             |  2 +
 system/lib/pthread/threading_internal.h       |  2 +
 test/other/test_proxied_main_keepalive_exit.c | 47 +++++++++++++++++++
 test/test_other.py                            | 15 ++++++
 6 files changed, 109 insertions(+)
 create mode 100644 test/other/test_proxied_main_keepalive_exit.c

diff --git a/src/lib/libcore.js b/src/lib/libcore.js
index 928777d174877..5be61f8984b79 100644
--- a/src/lib/libcore.js
+++ b/src/lib/libcore.js
@@ -113,6 +113,9 @@ addToLibrary({
 #if PTHREADS
     '$exitOnMainThread',
 #endif
+#if PROXY_TO_PTHREAD
+    '$proxiedMainDone',
+#endif
 #if PTHREADS_DEBUG || ASSERTIONS
     '$runtimeKeepaliveCounter',
 #endif
@@ -132,6 +135,10 @@ addToLibrary({
 #endif
 #if PTHREADS_DEBUG
       dbg(`Pthread ${ptrToString(_pthread_self())} called exit(${status}), posting exitOnMainThread.`);
+#endif
+#if PROXY_TO_PTHREAD
+      // Forget a waiting main return.
+      proxiedMainDone = false;
 #endif
       // When running in a pthread we propagate the exit back to the main thread
       // where it can decide if the whole process should be shut down or not.
@@ -2169,6 +2176,11 @@ addToLibrary({
 #if PTHREADS
     '_emscripten_thread_exit',
 #endif
+#if PROXY_TO_PTHREAD
+    '$proxiedMainDone',
+    '$proxiedMainExitCode',
+    '$exitOnMainThread',
+#endif
 #if RUNTIME_DEBUG >= 2
     '$runtimeKeepaliveCounter',
 #endif
@@ -2192,6 +2204,14 @@ addToLibrary({
           // exit the current thread, but only if there is one active.
           // TODO(https://github.com/emscripten-core/emscripten/issues/25076):
           // Unify this check with the runtimeExited check above
+#if PROXY_TO_PTHREAD && EXIT_RUNTIME
+          // Run a waiting main return once.
+          if (proxiedMainDone) {
+            proxiedMainDone = false;
+            exitOnMainThread(proxiedMainExitCode);
+            return;
+          }
+#endif
           if (_pthread_self()) __emscripten_thread_exit(EXITSTATUS);
           return;
         }
diff --git a/src/lib/libpthread.js b/src/lib/libpthread.js
index 7e68b6e14d7d8..38367fc030b87 100644
--- a/src/lib/libpthread.js
+++ b/src/lib/libpthread.js
@@ -986,6 +986,20 @@ var LibraryPThread = {
     _exit(returnCode);
   },
 
+#if PROXY_TO_PTHREAD
+  // Main's return, saved for maybeExit.
+  $proxiedMainDone__internal: true,
+  $proxiedMainDone: false,
+  $proxiedMainExitCode__internal: true,
+  $proxiedMainExitCode: 0,
+
+  __emscripten_proxied_main_done__deps: ['$proxiedMainDone', '$proxiedMainExitCode'],
+  __emscripten_proxied_main_done: (status) => {
+    proxiedMainDone = true;
+    proxiedMainExitCode = status;
+  },
+#endif
+
 #if MEMORY64
   // Calls proxyToMainThread but returns a bigint rather than a number
   $proxyToMainThreadPtr__deps: ['$proxyToMainThread'],
@@ -1144,6 +1158,10 @@ var LibraryPThread = {
 #if !MINIMAL_RUNTIME
     '$keepRuntimeAlive',
     '$runtimeKeepaliveCounter',
+#endif
+#if PROXY_TO_PTHREAD
+    '$proxiedMainDone',
+    '$proxiedMainExitCode',
 #endif
   ],
   $invokeEntryPoint: {{{ asyncIf(ASYNCIFY == 2) }}}(ptr, arg) => {
@@ -1166,6 +1184,11 @@ var LibraryPThread = {
     noExitRuntime = 0;
 #endif
 #endif
+#if PROXY_TO_PTHREAD
+    // No main return waiting yet.
+    proxiedMainDone = false;
+    proxiedMainExitCode = 0;
+#endif
 
 #if MAIN_MODULE
     // Before we call the thread entry point, make sure any shared libraries
diff --git a/system/lib/libc/crt1_proxy_main.c b/system/lib/libc/crt1_proxy_main.c
index 2d178ca2e473a..e21c062dc7e11 100644
--- a/system/lib/libc/crt1_proxy_main.c
+++ b/system/lib/libc/crt1_proxy_main.c
@@ -32,6 +32,8 @@ static void* _main_thread(void* param) {
   if (!emscripten_runtime_keepalive_check()) {
     exit(rtn);
   }
+  // Wait for keepalives, then exit with main's status.
+  __emscripten_proxied_main_done(rtn);
   return NULL;
 }
 
diff --git a/system/lib/pthread/threading_internal.h b/system/lib/pthread/threading_internal.h
index 097595e3ba6b9..0e62c97081ac0 100644
--- a/system/lib/pthread/threading_internal.h
+++ b/system/lib/pthread/threading_internal.h
@@ -63,6 +63,8 @@ void _emscripten_init_main_thread_js(void* tb);
 void _emscripten_thread_profiler_enable();
 void _emscripten_thread_cleanup(pthread_t thread);
 
+void __emscripten_proxied_main_done(int status);
+
 hidden void* _emscripten_tls_init(void);
 hidden void _emscripten_tls_free(void);
 
diff --git a/test/other/test_proxied_main_keepalive_exit.c b/test/other/test_proxied_main_keepalive_exit.c
new file mode 100644
index 0000000000000..949a89bde444a
--- /dev/null
+++ b/test/other/test_proxied_main_keepalive_exit.c
@@ -0,0 +1,47 @@
+// Proxied main must exit with its status after keepalives run.
+#include <emscripten.h>
+#include <emscripten/eventloop.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void at_exit(void) { printf("done\n"); }
+
+#ifdef MODE_CLEARED
+int long_id;
+
+void never(void* arg) {
+  printf("cleared callback ran\n");
+  abort();
+}
+#endif
+
+void fired(void* arg) {
+  printf("fired\n");
+#ifdef MODE_CLEARED
+  emscripten_clear_timeout(long_id);
+#elif defined(MODE_FORCE_EXIT)
+  // exit() beats a waiting return.
+  emscripten_force_exit(7);
+#elif defined(MODE_EXIT)
+  exit(7);
+#endif
+}
+
+int main(void) {
+#ifdef MODE_NEGATIVE
+  // Check the value, not just the code.
+  MAIN_THREAD_EM_ASM({ Module['onExit'] = (c) => { out('exited:' + c); }; });
+#else
+  MAIN_THREAD_EM_ASM({ Module['onExit'] = () => { out('exited'); }; });
+#endif
+  atexit(at_exit);
+#ifdef MODE_CLEARED
+  long_id = emscripten_set_timeout(never, 10000, NULL);
+#endif
+  emscripten_set_timeout(fired, 10, NULL);
+#ifdef MODE_NEGATIVE
+  return -1;
+#else
+  return 3;
+#endif
+}
diff --git a/test/test_other.py b/test/test_other.py
index bd63374a7c13b..7eba2116a1916 100644
--- a/test/test_other.py
+++ b/test/test_other.py
@@ -11603,6 +11603,21 @@ def test_proxy_to_pthread_stack(self):
                             '-sSTACK_SIZE=128kb', '-sEXIT_RUNTIME',
                             '--profiling-funcs'])
 
+  @requires_pthreads
+  @parameterized({
+    '': ([], 3, 'fired\ndone\nexited\n'),
+    'cleared': (['-DMODE_CLEARED'], 3, 'fired\ndone\nexited\n'),
+    'force_exit': (['-DMODE_FORCE_EXIT'], 7, 'fired\ndone\nexited\n'),
+    'exit': (['-DMODE_EXIT'], 7, 'fired\ndone\nexited\n'),
+    'negative': (['-DMODE_NEGATIVE'], NON_ZERO, 'fired\ndone\nexited:-1\n'),
+  })
+  def test_proxied_main_keepalive_exit(self, cflags, returncode, expected):
+    # See https://github.com/emscripten-core/emscripten/issues/27721
+    # Proxied main that returns with a keepalive must exit with its status.
+    self.do_runf('other/test_proxied_main_keepalive_exit.c', expected,
+                 cflags=['-pthread', '-sPROXY_TO_PTHREAD', '-sEXIT_RUNTIME'] + cflags,
+                 assert_returncode=returncode)
+
   @crossplatform
   @no_windows('ptys and select are not available on windows')
   def test_color_diagnostics(self):

From 7e5e091e8272636c8e9b4fa7bde8874885cf14d6 Mon Sep 17 00:00:00 2001
From: Nate Bracy <nate@bracy.dev>
Date: Thu, 17 Sep 2026 21:06:56 -0400
Subject: [PATCH 2/3] nit: simplify main exit status

---
 src/lib/libcore.js                      | 3 +--
 src/lib/libpthread.js                   | 9 ++-------
 system/lib/libc/crt1_proxy_main.c       | 4 ++--
 system/lib/pthread/threading_internal.h | 2 +-
 4 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/src/lib/libcore.js b/src/lib/libcore.js
index 5be61f8984b79..8efacb26ca958 100644
--- a/src/lib/libcore.js
+++ b/src/lib/libcore.js
@@ -2178,7 +2178,6 @@ addToLibrary({
 #endif
 #if PROXY_TO_PTHREAD
     '$proxiedMainDone',
-    '$proxiedMainExitCode',
     '$exitOnMainThread',
 #endif
 #if RUNTIME_DEBUG >= 2
@@ -2208,7 +2207,7 @@ addToLibrary({
           // Run a waiting main return once.
           if (proxiedMainDone) {
             proxiedMainDone = false;
-            exitOnMainThread(proxiedMainExitCode);
+            exitOnMainThread(EXITSTATUS);
             return;
           }
 #endif
diff --git a/src/lib/libpthread.js b/src/lib/libpthread.js
index 38367fc030b87..598a6da0028a1 100644
--- a/src/lib/libpthread.js
+++ b/src/lib/libpthread.js
@@ -990,13 +990,10 @@ var LibraryPThread = {
   // Main's return, saved for maybeExit.
   $proxiedMainDone__internal: true,
   $proxiedMainDone: false,
-  $proxiedMainExitCode__internal: true,
-  $proxiedMainExitCode: 0,
 
-  __emscripten_proxied_main_done__deps: ['$proxiedMainDone', '$proxiedMainExitCode'],
-  __emscripten_proxied_main_done: (status) => {
+  __emscripten_proxied_main_done__deps: ['$proxiedMainDone'],
+  __emscripten_proxied_main_done: () => {
     proxiedMainDone = true;
-    proxiedMainExitCode = status;
   },
 #endif
 
@@ -1161,7 +1158,6 @@ var LibraryPThread = {
 #endif
 #if PROXY_TO_PTHREAD
     '$proxiedMainDone',
-    '$proxiedMainExitCode',
 #endif
   ],
   $invokeEntryPoint: {{{ asyncIf(ASYNCIFY == 2) }}}(ptr, arg) => {
@@ -1187,7 +1183,6 @@ var LibraryPThread = {
 #if PROXY_TO_PTHREAD
     // No main return waiting yet.
     proxiedMainDone = false;
-    proxiedMainExitCode = 0;
 #endif
 
 #if MAIN_MODULE
diff --git a/system/lib/libc/crt1_proxy_main.c b/system/lib/libc/crt1_proxy_main.c
index e21c062dc7e11..d71a44d4d48b4 100644
--- a/system/lib/libc/crt1_proxy_main.c
+++ b/system/lib/libc/crt1_proxy_main.c
@@ -33,8 +33,8 @@ static void* _main_thread(void* param) {
     exit(rtn);
   }
   // Wait for keepalives, then exit with main's status.
-  __emscripten_proxied_main_done(rtn);
-  return NULL;
+  __emscripten_proxied_main_done();
+  return (void*)(intptr_t)rtn;
 }
 
 EMSCRIPTEN_KEEPALIVE int _emscripten_proxy_main(int argc, char** argv) {
diff --git a/system/lib/pthread/threading_internal.h b/system/lib/pthread/threading_internal.h
index 0e62c97081ac0..f568d6d1bfbc8 100644
--- a/system/lib/pthread/threading_internal.h
+++ b/system/lib/pthread/threading_internal.h
@@ -63,7 +63,7 @@ void _emscripten_init_main_thread_js(void* tb);
 void _emscripten_thread_profiler_enable();
 void _emscripten_thread_cleanup(pthread_t thread);
 
-void __emscripten_proxied_main_done(int status);
+void __emscripten_proxied_main_done(void);
 
 hidden void* _emscripten_tls_init(void);
 hidden void _emscripten_tls_free(void);

From d49fcc78b984b0ce3f0cdd88baff273fe6063445 Mon Sep 17 00:00:00 2001
From: Nate Bracy <nate@bracy.dev>
Date: Sat, 19 Sep 2026 21:30:11 -0400
Subject: [PATCH 3/3] nit: drop proxiedMainDone in favor of isProxiedMainThread

---
 src/lib/libcore.js                      | 24 ++++++------------------
 src/lib/libpthread.js                   | 24 ++++++++++++++----------
 system/lib/libc/crt1_proxy_main.c       |  9 +++------
 system/lib/pthread/threading_internal.h |  2 +-
 4 files changed, 24 insertions(+), 35 deletions(-)

diff --git a/src/lib/libcore.js b/src/lib/libcore.js
index 8efacb26ca958..2e93d64553d15 100644
--- a/src/lib/libcore.js
+++ b/src/lib/libcore.js
@@ -113,9 +113,6 @@ addToLibrary({
 #if PTHREADS
     '$exitOnMainThread',
 #endif
-#if PROXY_TO_PTHREAD
-    '$proxiedMainDone',
-#endif
 #if PTHREADS_DEBUG || ASSERTIONS
     '$runtimeKeepaliveCounter',
 #endif
@@ -135,10 +132,6 @@ addToLibrary({
 #endif
 #if PTHREADS_DEBUG
       dbg(`Pthread ${ptrToString(_pthread_self())} called exit(${status}), posting exitOnMainThread.`);
-#endif
-#if PROXY_TO_PTHREAD
-      // Forget a waiting main return.
-      proxiedMainDone = false;
 #endif
       // When running in a pthread we propagate the exit back to the main thread
       // where it can decide if the whole process should be shut down or not.
@@ -2177,8 +2170,7 @@ addToLibrary({
     '_emscripten_thread_exit',
 #endif
 #if PROXY_TO_PTHREAD
-    '$proxiedMainDone',
-    '$exitOnMainThread',
+    '$isProxiedMainThread',
 #endif
 #if RUNTIME_DEBUG >= 2
     '$runtimeKeepaliveCounter',
@@ -2199,18 +2191,14 @@ addToLibrary({
 #endif
       try {
 #if PTHREADS
-        if (ENVIRONMENT_IS_PTHREAD) {
+        if (ENVIRONMENT_IS_PTHREAD
+#if PROXY_TO_PTHREAD
+            && !isProxiedMainThread
+#endif
+        ) {
           // exit the current thread, but only if there is one active.
           // TODO(https://github.com/emscripten-core/emscripten/issues/25076):
           // Unify this check with the runtimeExited check above
-#if PROXY_TO_PTHREAD && EXIT_RUNTIME
-          // Run a waiting main return once.
-          if (proxiedMainDone) {
-            proxiedMainDone = false;
-            exitOnMainThread(EXITSTATUS);
-            return;
-          }
-#endif
           if (_pthread_self()) __emscripten_thread_exit(EXITSTATUS);
           return;
         }
diff --git a/src/lib/libpthread.js b/src/lib/libpthread.js
index 598a6da0028a1..2fb3349cf0419 100644
--- a/src/lib/libpthread.js
+++ b/src/lib/libpthread.js
@@ -987,13 +987,12 @@ var LibraryPThread = {
   },
 
 #if PROXY_TO_PTHREAD
-  // Main's return, saved for maybeExit.
-  $proxiedMainDone__internal: true,
-  $proxiedMainDone: false,
+  $isProxiedMainThread__internal: true,
+  $isProxiedMainThread: false,
 
-  __emscripten_proxied_main_done__deps: ['$proxiedMainDone'],
-  __emscripten_proxied_main_done: () => {
-    proxiedMainDone = true;
+  __emscripten_set_proxied_main_thread__deps: ['$isProxiedMainThread'],
+  __emscripten_set_proxied_main_thread: () => {
+    isProxiedMainThread = true;
   },
 #endif
 
@@ -1157,7 +1156,8 @@ var LibraryPThread = {
     '$runtimeKeepaliveCounter',
 #endif
 #if PROXY_TO_PTHREAD
-    '$proxiedMainDone',
+    '$isProxiedMainThread',
+    'exit',
 #endif
   ],
   $invokeEntryPoint: {{{ asyncIf(ASYNCIFY == 2) }}}(ptr, arg) => {
@@ -1181,8 +1181,7 @@ var LibraryPThread = {
 #endif
 #endif
 #if PROXY_TO_PTHREAD
-    // No main return waiting yet.
-    proxiedMainDone = false;
+    isProxiedMainThread = false;
 #endif
 
 #if MAIN_MODULE
@@ -1208,13 +1207,18 @@ var LibraryPThread = {
 #endif
     function finish(result) {
 #if !MINIMAL_RUNTIME
+      EXITSTATUS = result;
       // In MINIMAL_RUNTIME the noExitRuntime concept does not apply to
       // pthreads. To exit a pthread with live runtime, use the function
       // emscripten_unwind_to_js_event_loop() in the pthread body.
       if (keepRuntimeAlive()) {
-        EXITSTATUS = result;
         return;
       }
+#endif
+#if PROXY_TO_PTHREAD
+      if (isProxiedMainThread) {
+        _exit(result);
+      }
 #endif
       __emscripten_thread_exit(result);
     }
diff --git a/system/lib/libc/crt1_proxy_main.c b/system/lib/libc/crt1_proxy_main.c
index d71a44d4d48b4..37d5008beee8f 100644
--- a/system/lib/libc/crt1_proxy_main.c
+++ b/system/lib/libc/crt1_proxy_main.c
@@ -8,10 +8,11 @@
 #include <pthread.h>
 #include <stdlib.h>
 
+#include <stdint.h>
+
 #include <emscripten.h>
 #include <emscripten/stack.h>
 #include <emscripten/threading.h>
-#include <emscripten/eventloop.h>
 
 #include "threading_internal.h"
 
@@ -27,13 +28,9 @@ weak int __main_void(void) {
 static void* _main_thread(void* param) {
   // This is the main runtime thread for the application.
   emscripten_set_thread_name(pthread_self(), "Application main thread");
+  __emscripten_set_proxied_main_thread();
   // Will either call user's __main_void or weak version above.
   int rtn = __main_void();
-  if (!emscripten_runtime_keepalive_check()) {
-    exit(rtn);
-  }
-  // Wait for keepalives, then exit with main's status.
-  __emscripten_proxied_main_done();
   return (void*)(intptr_t)rtn;
 }
 
diff --git a/system/lib/pthread/threading_internal.h b/system/lib/pthread/threading_internal.h
index f568d6d1bfbc8..73df3a0ab057b 100644
--- a/system/lib/pthread/threading_internal.h
+++ b/system/lib/pthread/threading_internal.h
@@ -63,7 +63,7 @@ void _emscripten_init_main_thread_js(void* tb);
 void _emscripten_thread_profiler_enable();
 void _emscripten_thread_cleanup(pthread_t thread);
 
-void __emscripten_proxied_main_done(void);
+void __emscripten_set_proxied_main_thread(void);
 
 hidden void* _emscripten_tls_init(void);
 hidden void _emscripten_tls_free(void);