I'm investigating spurious awakes in both the standard and this executor.
See ros2/rclcpp#1021 for the standard executor

The problem mentioned in the ticket above does not appear in the static executor when I run that dummy executable with only 1 timer.
However, if I run a system made of 2 nodes (1 pub and 1 sub) in the same executor with IPC on, I see the exact same pattern.

I think that the root cause is how the static executor handles the waitable objects:
in each "iteration" of the static executor:

• timer makes the publisher to publish a message. It's intra-process only, so the message is pushed into the subscription queue and the condition variable is triggered.
• the executor checks waitable objects only through the is_ready() condition, that in this case consists in checking if the buffer is not empty. Since a message has just been pushed, the IPC subscription is invoked.
• the executor goes back to wait
• the executor wakes up immediately due to the condition variable triggered by the publisher above
• there is no work to do
• the executor goes back to wait

@MartinCornelis2 what do you think? I think that this problem with IPC is not present with the standard executor because only 1 item is processed in every iteration and the waitables are managed by the memory strategy.