cancel timer before letting caller use the node to avoid spurious wakeups for consumers

[mikaelarguedas]

@dirk-thomas Is this timer intended to stay alive and be used by consumers?

Otherwise I can update this PR to destroy the timer before exiting the init function

[dirk-thomas]

I don't think the timer is used anywhere. It could be made "internal" to the constructor and be destroyed immediately.

[mikaelarguedas]

Sounds good updated in cbe14dd

[dirk-thomas]

lgtm

(Since the ticket doesn't mention any reproducible example I didn't try the patch.)

[mikaelarguedas]

It can be reproduced by adding a print in the timer callback.

         def timer_callback():
             nonlocal timeout_reached
+            print('timer_cb')
             timeout_reached = True

In one terminal run: ros2 run demo_nodes_cpp talker
In the second one run: ros2 topic echo /chatter std_msgs/String

Behavior without the patch

$ ros2 topic echo /chatter std_msgs/String
timer_cb
timer_cb
timer_cb
timer_cb
timer_cb
timer_cb
timer_cb
timer_cb
data: 'Hello World: 1'

timer_cb
timer_cb
data: 'Hello World: 2'

timer_cb
timer_cb
data: 'Hello World: 3'

timer_cb
timer_cb
data: 'Hello World: 4'

timer_cb
timer_cb

Behavior with the patch

$ ros2 topic echo /chatter std_msgs/String
timer_cb
data: 'Hello World: 1'

data: 'Hello World: 2'

data: 'Hello World: 3'

data: 'Hello World: 4'