How to handle a blocking function inside a node?

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You can check this nice repository https://github.com/DLu/toy_threads for the second option with threading with rclpy:

toy_threads

Some toy examples to demonstrate threading in rclpy.

tl;dr: To achieve parallel tasks using rclpy you must use BOTH a MultiThreadedExecutor AND custom Callback Groups!!

Yeah both options are valid, and if you go down the threading option, you might avoid writing some of the thread creation logic by using a MultiThreadedExecutor.

Personally I think I might vote for option 1 in this case if you aren't insanely resource constrained. I've been finding small, single-threaded, single-purpose nodes to be easier to debug and reason about and it avoids you needing to consider any multi-threaded locking mechanisms in your code (which are easy to get wrong). If you're already running Python on your target system you probably don't need to worry too much about the small overhead of an extra ROS node vs combining into a single node.

You can probably use rclpy.executors.MultiThreadedExecutor() to achieve what you want.

This example shows you how to implement it in ROS 2 foxy.