Add service example

[evaan]

No description provided.

[okyer]

How to use spin, Why is it sometimes possible and sometimes not, when I call service.

First run service:
service_client/service$ ./service

After run client on the other terminal:
service_client/client$ ./client
69

But it's sometimes output result 69 and sometimes not, It seems to be blocked, output nothing.

Run this command, receive results every time without blocking. So there are no issues with the service, there is a problem with the client. By check the client code, I believe it is an issue with the spin function
$ ros2 service call /test/add example_srvs/srv/AddTwoInts '{a: 11, b: 20}'

waiting for service to become available...
requester: making request: example_srvs.srv.AddTwoInts_Request(a=11, b=20)
response:
example_srvs.srv.AddTwoInts_Response(sum=31)

Can you help me, improve this code?

[sebdeveloper6952]

@okyer I've ran into the same issue and I don't understand yet why. Following this tutorial though, i've added a time.Sleep(time.Second) call in between Spin and client.Send. That seems to have fixed some sort of race condition when Spin does its initialization.