Fix TSAN race condition in FileLogger2 with condition_variable

Use proper condition_variable synchronization to ensure the writer
thread is fully ready before the constructor returns. This prevents
race conditions where callbacks fire before the thread is initialized.

Previous atomic-based approach still had TSAN warnings because the
callback could start executing while the constructor was blocked
waiting for the condition variable, causing a double-lock scenario.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: facontidavide

src/loggers/bt_file_logger_v2.cpp

@@ -27,7 +27,11 @@ struct FileLogger2::PImpl
 
   std::thread writer_thread;
   std::atomic_bool loop = true;
-  std::atomic_bool ready = false;  // Set to true when writer thread is running
+
+  // Synchronization for thread startup
+  std::mutex ready_mutex;
+  std::condition_variable ready_cv;
+  bool ready = false;
 };
 
 FileLogger2::FileLogger2(const BT::Tree& tree, std::filesystem::path const& filepath)
@@ -72,6 +76,13 @@ FileLogger2::FileLogger2(const BT::Tree& tree, std::filesystem::path const& file
   _p->file_stream.write(write_buffer.data(), 8);
 
   _p->writer_thread = std::thread(&FileLogger2::writerLoop, this);
+
+  // Wait for writer thread to be ready before returning
+  // This prevents race conditions where callbacks fire before thread is initialized
+  {
+    std::unique_lock<std::mutex> lock(_p->ready_mutex);
+    _p->ready_cv.wait(lock, [this]() { return _p->ready; });
+  }
 }
 
 FileLogger2::~FileLogger2()
@@ -85,12 +96,6 @@ FileLogger2::~FileLogger2()
 void FileLogger2::callback(Duration timestamp, const TreeNode& node,
                            NodeStatus /*prev_status*/, NodeStatus status)
 {
-  // Wait until the writer thread is ready to avoid race during construction
-  if(!_p->ready.load(std::memory_order_acquire))
-  {
-    return;
-  }
-
   Transition trans{};
   trans.timestamp_usec = uint64_t(ToUsec(timestamp - _p->first_timestamp));
   trans.node_uid = node.UID();
@@ -110,7 +115,11 @@ void FileLogger2::flush()
 void FileLogger2::writerLoop()
 {
   // Signal that the writer thread is ready to accept callbacks
-  _p->ready.store(true, std::memory_order_release);
+  {
+    std::lock_guard<std::mutex> lock(_p->ready_mutex);
+    _p->ready = true;
+  }
+  _p->ready_cv.notify_one();
 
   // local buffer in this thread
   std::deque<Transition> transitions;