Spin recorder node in a separate thread for better handling exit

- Run exec->spin() in a separate thread, because we need to call
exec->cancel() after recorder->stop() to be able to send notifications
about bag split and close.
- Wait on conditional variable for exit_ flag

Signed-off-by: Michael Orlov <[email protected]>

rosbag2_py/src/rosbag2_py/_transport.cpp

@@ -189,19 +189,13 @@ class Player
 
 class Recorder
 {
-private:
-  using ExecutorT = rclcpp::executors::SingleThreadedExecutor;
-  std::unique_ptr<ExecutorT> exec_;
-  std::shared_ptr<rosbag2_transport::Recorder> recorder_;
-
 public:
   Recorder()
   {
     auto init_options = rclcpp::InitOptions();
     init_options.shutdown_on_signal = false;
     rclcpp::init(0, nullptr, init_options, rclcpp::SignalHandlerOptions::None);
 
-    exec_ = std::make_unique<ExecutorT>();
     std::signal(
       SIGTERM, [](int /* signal */) {
         rosbag2_py::Recorder::cancel();
@@ -222,42 +216,52 @@ class Recorder
     RecordOptions & record_options,
     std::string & node_name)
   {
+    exit_ = false;
+    auto exec = std::make_unique<rclcpp::executors::SingleThreadedExecutor>();
     if (record_options.rmw_serialization_format.empty()) {
       record_options.rmw_serialization_format = std::string(rmw_get_serialization_format());
     }
 
     auto writer = rosbag2_transport::ReaderWriterFactory::make_writer(record_options);
-    recorder_ = std::make_shared<rosbag2_transport::Recorder>(
+    auto recorder = std::make_shared<rosbag2_transport::Recorder>(
       std::move(writer), storage_options, record_options, node_name);
-    recorder_->record();
+    recorder->record();
 
-    exec_->add_node(recorder_);
-    try {
+    exec->add_node(recorder);
+    // Run exec->spin() in a separate thread, because we need to call exec->cancel() after
+    // recorder->stop() to be able to send notifications about bag split and close.
+    auto spin_thread = std::thread(
+      [&exec]() {
+        exec->spin();
+      });
+    {
       // Release the GIL for long-running record, so that calling Python code can use other threads
       py::gil_scoped_release release;
-      while (!exit_) {
-        exec_->spin_all(std::chrono::milliseconds(10));
-      }
-      if (recorder_) {
-        recorder_->stop();
-        // Need to spin node to be able to send notifications about bag split and close
-        exec_->spin_all(std::chrono::milliseconds(10));
-      }
-    } catch (...) {
-      exec_->remove_node(recorder_);
+      std::unique_lock<std::mutex> lock(wait_for_exit_mutex_);
+      wait_for_exit_cv_.wait(lock, [] {return rosbag2_py::Recorder::exit_.load();});
+      recorder->stop();
+    }
+    exec->cancel();
+    if (spin_thread.joinable()) {
+      spin_thread.join();
     }
-    exec_->remove_node(recorder_);
+    exec->remove_node(recorder);
   }
 
   static void cancel()
   {
     exit_ = true;
+    wait_for_exit_cv_.notify_all();
   }
 
+protected:
   static std::atomic_bool exit_;
+  static std::condition_variable wait_for_exit_cv_;
+  std::mutex wait_for_exit_mutex_;
 };
 
 std::atomic_bool Recorder::exit_{false};
+std::condition_variable Recorder::wait_for_exit_cv_{};
 
 // Return a RecordOptions struct with defaults set for rewriting bags.
 rosbag2_transport::RecordOptions bag_rewrite_default_record_options()