How to build system to check the incoming messages in GWT?

Ok, I got a message system, user can send message to each other at any time. The message icon is in the header. I want to program so that when person A sends a message to person B, then B can be able to see the message in the header immediately & automatically without needing to refresh the page.

How does that system work?

I think there some solutions here,

-Solution1: we program so that each active page will check the message every 5 minutes. This is not too smart since if there's no message, the server still receives the call every 5 min. Imagine there is a million users & if each user opens the page & lives the page for the whole day then server will receive too many unnecessary calls.

-Solution2: Do some sort of global variable that check the incoming message. When A sends message to B, the global variable will be changed, & we needs to do something so that that variable can check all the active pages that user B is opening & the system sends the reminder to all those pages. I am not sure if this is the right way to do.

Can you find a better solution?

Does anyone know what is the wright way to build this system?

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