Callback to main thread

Hi,

I am working on C++ InDesign UI plugin, which interacts with document. The plugin is waiting for orders from outside the plugin, for which it starts a background thread, which is polling a socket periodically. If any change is detected, then it callbacks to the main thread where we can update UI. 

However i got stuck at calling back to the main thread. I tried to use commands to notify the main thread, there is some change that it needed to handle. However i cannot queue commands in the background thread (at least it crashes).

Do you know about any workaround? Or how can i achive this behaviour (constantly, endlessly polling service, and based on that fire an "event" for the main thread to change the text?

Thanks in advance,

Balazs