Fix fork-time deadlock between ConfigLoader and threadSafeForkPrepare

libkineto/src/ConfigLoader.cpp

@@ -166,13 +166,17 @@ void ConfigLoader::startThread() {
   }
 }
 
+void ConfigLoader::signalStop() {
+  stopFlag_ = true;
+  {
+    std::lock_guard<std::mutex> lock(updateThreadMutex_);
+    updateThreadCondVar_.notify_one();
+  }
+}
+
 void ConfigLoader::stopThread() {
+  signalStop();
   if (updateThread_) {
-    stopFlag_ = true;
-    {
-      std::lock_guard<std::mutex> lock(updateThreadMutex_);
-      updateThreadCondVar_.notify_one();
-    }
     if (updateThread_->joinable()) {
       updateThread_->join();
     }

libkineto/src/ConfigLoader.h

@@ -87,8 +87,13 @@ class ConfigLoader {
 
   std::string getConfString();
 
-  // Stop the background polling thread. Safe to call multiple times.
-  // Exposed for embedders that need to join the thread before other
+  // Signal the background polling thread to stop without joining it.
+  // Use this when joining is unsafe (e.g., the thread may be blocked on a
+  // lock held by the caller). The thread will exit on its next loop iteration.
+  void signalStop();
+
+  // Stop the background polling thread and join it. Safe to call multiple
+  // times. Exposed for embedders that need to join the thread before other
   // singletons are destroyed.
   void stopThread();