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1 | initial version |
You can see where it's useful slightly above:
https://github.com/ros2/geometry2/blob/7fb77c597e22344f90f5661f0871beedb666b73a/tf2_ros/include/tf2_ros/buffer.h#L217
or https://docs.ros2.org/foxy/api/tf2_ros/classtf2__ros_1_1Buffer.html#ad14c12577a86a981cb8853b571809551
This timer interface allows the buffer to register for regular callbacks from the node to test for the availability of the transform. This allows the buffer to fulfill it's asynchronous query without requiring starting its own thread(s).