Fix race condition in checkMailbox

The `checkMailbox` callback can occur after the thread has terminated.
In this case calling into native code can trigger the `makeAbortWrapper`
wrapper that is put around each native function which then results in a
"program has already aborted!" error being thrown.

Once solution to this is to make sure that the function which are called
do not have `makeAbortWrapper` applied to them.

This was the technique I used in #18754, but the list of functions
became stale when emscripten_proxy_execute_task_queue was removed in #18852.

A better solution is to wrap to whole function in callUserCallback,
which takes case of checking if the runtime is alive before calling into
native code.

Fixes: #20067

Author: sbc100

src/lib/libcore.js

@@ -2113,8 +2113,19 @@ addToLibrary({
   },
 
 #else // MINIMAL_RUNTIME
-  // MINIMAL_RUNTIME doesn't support the runtimeKeepalive stuff
-  $callUserCallback: (func) => func(),
+  $callUserCallback: (func) => {
+    // MINIMAL_RUNTIME doesn't support the runtimeKeepalive stuff, but under
+    // some circumstances it supportes `runtimeExited`
+#if EXIT_RUNTIME
+    if (runtimeExited) {
+#if ASSERTIONS
+      err('user callback triggered after runtime exited or application aborted.  Ignoring.');
+#endif
+      return;
+    }
+#endif
+    func();
+  },
 #endif // MINIMAL_RUNTIME
 
   $asmjsMangle: (x) => {

src/lib/libpthread.js

@@ -1215,19 +1215,23 @@ var LibraryPThread = {
                         'pthread_self',
                         '_emscripten_check_mailbox',
                         '_emscripten_thread_mailbox_await'],
-  $checkMailbox: () => {
+  $checkMailbox: () => callUserCallback(() => {
     // Only check the mailbox if we have a live pthread runtime. We implement
     // pthread_self to return 0 if there is no live runtime.
+    //
+    // TODO(sbc): Is this check still needed?  `callUserCallback` is supposed to
+    // ensure the runtime is alive, and if `_pthread_self` is NULL then the
+    // runtime certainly is *not* alive, so this should be a redundant check.
     var pthread_ptr = _pthread_self();
     if (pthread_ptr) {
       // If we are using Atomics.waitAsync as our notification mechanism, wait
       // for a notification before processing the mailbox to avoid missing any
       // work that could otherwise arrive after we've finished processing the
       // mailbox and before we're ready for the next notification.
       __emscripten_thread_mailbox_await(pthread_ptr);
-      callUserCallback(__emscripten_check_mailbox);
+      __emscripten_check_mailbox();
     }
-  },
+  }),
 
   _emscripten_thread_mailbox_await__deps: ['$checkMailbox'],
   _emscripten_thread_mailbox_await: (pthread_ptr) => {

tools/emscripten.py

@@ -897,9 +897,7 @@ def install_debug_wrapper(sym):
     return False
   # Likewise `__trap` can occur before the runtime is initialized since it is used in
   # abort.
-  # pthread_self is currently called in some cases after the runtime has exited.
-  # TODO: Look into removing these, and improving our robustness around thread termination.
-  return sym not in {'__trap', 'pthread_self'}
+  return sym != '__trap'
 
 
 def should_export(sym):