avoid redundant memory allocations in wait_for_work

[wjwwood]

This function, wait_for_work which is in the rclcpp::Executor class:

• rclcpp/rclcpp/include/rclcpp/executor.hpp

  Line 167 in 860f478

  wait_for_work(bool nonblocking)

• TODO's:

  • rclcpp/rclcpp/include/rclcpp/executor.hpp

    Line 211 in 860f478

    // TODO: Avoid redundant malloc's

  • rclcpp/rclcpp/include/rclcpp/executor.hpp

    Line 233 in 860f478

    // TODO: Avoid redundant malloc's

repeatedly malloc's for temporary storage used in the ros_middleware_interface::wait function.

This could be avoided either by only allocating memory when resizing of the structures is required or by always using a structure of the maximum possible size (still would need to be updated when nodes are added or removed but less frequently) and ensuring that the ros_middleware_interface::wait function properly handles the extra, unused storage.

[jackieokay]

This was resolved by #56, correct?

[wjwwood]

I don't think so because we still malloc and free each time we go through the loop. I think to resolve this ticket we need to have the default memory strategy only malloc or realloc when there is not enough space, otherwise reusing memory already allocated.

[jackieokay]

Fixed by #129