Change next_call_time computation of rcl_timer to always result in a future timestamp

[kohrt]

In the current implementation next_call_time can be equal to now after the timer has been called. This can lead to consecutive callback calls with the same timestamp when using sim time.

With this change next_call_time will always be greater than now after the timer has been called.

[kohrt]

I think, I didn't make it clear in the beginning. We have the issue that timer callbacks of our nodes get called twice with the same timestamp regularly when used in simulation with use_sim_time set to true. I tracked down the problem and tried to create a minimal change that fixes it.

[fujitatomoya]

I think, I didn't make it clear in the beginning. We have the issue that timer callbacks of our nodes get called twice with the same timestamp regularly when used in simulation with use_sim_time set to true. I tracked down the problem and tried to create a minimal change that fixes it.

@kohrt thanks for sharing the issue. is that possible to share the reproducible test project? that would be helpful to understand details and do further debug.

[kohrt]

Here is the example project: https://github.com/cellumation/timer_test.git

Compile and run ros2 launch timer_test timer_test.yaml. It will output if calls with the same timestamps occure:

[timer_test-1] [WARN] [1692347432.710947829] [timer_test]: same timestamp: 2600000000
[timer_test-1] [WARN] [1692347432.810938363] [timer_test]: same timestamp: 2700000000
[timer_test-1] [WARN] [1692347432.910990966] [timer_test]: same timestamp: 2800000000
[timer_test-1] [WARN] [1692347433.011015172] [timer_test]: same timestamp: 2900000000
[timer_test-1] [WARN] [1692347433.111107161] [timer_test]: same timestamp: 3000000000
[timer_test-1] [WARN] [1692347433.211355448] [timer_test]: same timestamp: 3100000000
[timer_test-1] [WARN] [1692347439.224457634] [timer_test]: same timestamp: 9110000000

[fujitatomoya]

@kohrt thanks for providing the test project, that really helped me to understand.

i did some experimental check and left a couple of comments, could you share your thought?

CC: @ros2/team

[fujitatomoya]

My local test project, see fujitatomoya/ros2_test_prover@544e615

with the following commands, we can reproduce the problem.

> colcon build --symlink-install --packages-select prover_rclcpp

### Terminal-1
> ros2 run prover_rclcpp rcl_1089 --ros-args -p use_sim_time:=true --ros-args --log-level debug

### Terminal-2
> ros2 run prover_rclcpp sim_clock_publisher 

[clalancette]

and run CI

Actually, that won't work because we've added some APIs in the meantime. @kohrt Can you please go ahead and rebase this? Once that is done I'll run CI.

[kohrt]

Should be rebased now. Thanks for the review @fujitatomoya and @clalancette

[clalancette]

CI:

• Linux
• Linux-aarch64
• Windows