if cache data exists, it needs to flush the data into the storage bef…

…ore shutdown (ros2#541)

fix ros2#540 
* if cache data exists, it needs to flush the data into the storage before shutdown.
* cache_ needs to reset after writing to storage.
* add reset_cache() method.

Signed-off-by: Tomoya.Fujita <Tomoya.Fujita@sony.com>

rosbag2_cpp/include/rosbag2_cpp/writers/sequential_writer.hpp

@@ -141,6 +141,9 @@ class ROSBAG2_CPP_PUBLIC SequentialWriter
   // Record TopicInformation into metadata
   void finalize_metadata();
 
+  // Flush data into storage, and reset cache
+  void reset_cache();
+
   // Helper method used by write to get the message in a format that is ready to be written.
   // Common use cases include converting the message using the converter or
   // performing other operations like compression on it

rosbag2_cpp/src/rosbag2_cpp/writers/sequential_writer.cpp

@@ -140,6 +140,7 @@ void SequentialWriter::reset()
     metadata_io_->write_metadata(base_folder_, metadata_);
   }
 
+  reset_cache();
   storage_.reset();  // Necessary to ensure that the storage is destroyed before the factory
   storage_factory_.reset();
 }
@@ -251,11 +252,7 @@ void SequentialWriter::write(std::shared_ptr<rosbag2_storage::SerializedBagMessa
     cache_.push_back(converted_msg);
     current_cache_size_ += converted_msg->serialized_data->buffer_length;
     if (current_cache_size_ >= max_cache_size_) {
-      storage_->write(cache_);
-      // reset cache
-      cache_.clear();
-      cache_.reserve(max_cache_size_);
-      current_cache_size_ = 0u;
+      reset_cache();
     }
   }
 }
@@ -312,5 +309,16 @@ void SequentialWriter::finalize_metadata()
   }
 }
 
+void SequentialWriter::reset_cache()
+{
+  // if cache data exists, it must flush the data into the storage
+  if (!cache_.empty()) {
+    storage_->write(cache_);
+    // reset cache
+    cache_.clear();
+    cache_.reserve(max_cache_size_);
+    current_cache_size_ = 0u;
+  }
+}
 }  // namespace writers
 }  // namespace rosbag2_cpp