add note indicating that spin_until_future_complete should be used only with futures generated by ROS entities

Signed-off-by: Alberto Soragna <[email protected]>

Author: alsora

rclcpp/include/rclcpp/executor.hpp

@@ -371,6 +371,9 @@ class Executor
    *   If the time spent inside the blocking loop exceeds this timeout, return a TIMEOUT return
    *   code.
    * \return The return code, one of `SUCCESS`, `INTERRUPTED`, or `TIMEOUT`.
+   * \note This method will check the future and the timeout only when the executor is woke up.
+   * If this future is unrelated to an executor's entity, this method will not detect correctly
+   * when it's completed.
    */
   template<typename FutureT, typename TimeRepT = int64_t, typename TimeT = std::milli>
   FutureReturnCode