launch node can't dispaly RCLCPP_INFO infomation immediately

[ccy89]

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • binaries
• Version or commit hash:
  • dashing
• DDS implementation:
  • Fast-RTPS
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

use ros2/examples to test ros2 launch. Create a launch file with the following content and launch it.

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='examples_rclcpp_minimal_subscriber',
            node_executable='subscriber_lambda',
            node_name='subscriber_demo',
            output='screen',
        ),
        Node(
            package='examples_rclcpp_minimal_publisher',
            node_executable='publisher_lambda',
            node_name='publisher_demo',
            output='screen',
        ),
    ])

Expected behavior

The terminal will display node's INFO message immediately, like:

[subscriber_lambda-1] [INFO] [subscriber_demo]: I heard: 'Hello, world! 0'

Actual behavior

The terminal does not display any information at the beginning:

After a while, the terminal displays all information at once.

just like the subscriber is blocking.

Additional information

I run the command

ros2 topic echo /topic

I can echo "/topic" normally.

Is this a bug, or is it like this?

[ivanpauno]

Check #188 and ros2/rcutils#168.
Closing as duplicate.