@jwang11 @gaoethan @testkit In order to integrate the various changes from the https://github.com/intel/ros2_message_filters repository here please create separate PRs for separate /unrelated changes:

• remove no more relevant (ROS 1 specific) code
• add additional files from other repositories (e.g. MessageEvent) - depending on the amount of code the history might be good to keep (?)
• refactor code from Boost to std
• update source code, tests, CMake, manifest to ament / ROS 2
• (anything I missed while looking through the "diff" in the intel repo)

By making separate PRs with orthogonal changes it will be easier / quicker to review / iterate /merge them.