Rqt subscriber plugin (spin::once or asyncronous?

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Hello everyone I am new in rqt and I have some question I can not solve in the ROS wiki.

I already created a rqt plugin and I subscribe with the plugin to my topic and i tried to create another one that subscribe to another topic. The thing is that both topics and messages are generated by the same publisher so the plugins can not receive the data at the same time. So, How is it working the Plugin class spinner? Is it asyncronous or is publisher thread block every time a callback is processed?. Can I change that?

Thanks a lot.